Tryptophan | C11H12N2O2 | Amino Acid Database

Generic NameIDType
TryptophanAADB0018Essential
The essential amino acid l-tryptophan (Trp) is needed for the synthesis of proteins, serotonin, melatonin, and niacin. Utilization as an energy fuel depends on adequate availability of thiamin, riboflavin, vitamin B6, niacin, pantothenate, lipoate, ubiquinone, magnesium, and iron. Adequate amounts are consumed when total protein intake meets recommendations since dietary proteins from different sources all contain Trp. The protein in milk and dairy products contains slightly more than most other food proteins; corn protein contains less. Exposure to high heat as in grilling and frying can reduce the Trp content of food. Manufactured Trp is little used now, because in the past, contaminants have caused severe and irreversible harm (i.e., EOS). The same contaminants, as well as related ones, have been found in manufactured 5-hydroxytryptophan and melatonin. Adults are thought to require 6mg/kg per clay (Young and Borgonha, 2000). Prolonged lack of Trp, as with all essential amino acids or a lack of protein, causes growth failure, loss of muscle mass, and organ damage.Excessive intake: Very high intake of protein and mixed amino acids (i.e., more than three times the RDA (recommended dietary allowance), equivalent to 2.4 g/kg) is thought to increase the risk of renal glomerular sclerosis and accelerate osteoporosis. The consequences of very high intake of Trp, other than the known risks associated with toxic contaminants, have not been adequately evaluated.(Kohlmeier 2015)
Amino acid ClassSide Chain Type
AromaticNon-polar, aromatic
Kohlmeier, M. (2015). Nutrient metabolism: Structures, functions, and genes (2nd Edition). Academic Press. 10.1016/C2010-0-64980-7
DrugBank
Drugbank: DB00150
An essential amino acid that is necessary for normal growth in infants and for nitrogen balance in adults. It is a precursor of indole alkaloids in plants. It is a precursor of serotonin (hence its use as an antidepressant and sleep aid). It can be a precursor to niacin, albeit inefficiently, in mammals.
Descriptions
ChEBI
ChEBI :16977

L-tryptophan is the L-enantiomer of tryptophan. It has a role as an antidepressant, a nutraceutical, a micronutrient, a plant metabolite, a human metabolite, a Saccharomyces cerevisiae metabolite, an Escherichia coli metabolite and a mouse metabolite. It is an erythrose 4-phosphate/phosphoenolpyruvate family amino acid, a proteinogenic amino acid, a tryptophan and a L-alpha-amino acid. It is a conjugate base of a L-tryptophanium. It is a conjugate acid of a L-tryptophanate. It is an enantiomer of a D-tryptophan. It is a tautomer of a L-tryptophan zwitterion.

MeSH
MeSH

1: Tryptophan An essential amino acid that is necessary for normal growth in infants and for NITROGEN balance in adults. It is a precursor of INDOLE ALKALOIDS in plants. It is a precursor of SEROTONIN (hence its use as an antidepressant and sleep aid). It can be a precursor to NIACIN, albeit inefficiently, in mammals.

T3DB
T3DB

Tryptophan is an essential amino acid that is the precursor of both serotonin and melatonin. Melatonin is a hormone that is produced by the pineal gland in animals, which regulates sleep and wakefulness. Serotonin is a brain neurotransmitter, platelet clotting factor, and neurohormone found in organs throughout the body. Metabolism of tryptophan into serotonin requires nutrients such as vitamin B6, niacin, and glutathione. Niacin (also known as vitamin B3) is an important metabolite of tryptophan. It is synthesized via kynurenine and quinolinic acids, which are products of tryptophan degradation. There are a number of conditions or diseases that are characterized tryptophan deficiencies. For instance, fructose malabsorption causes improper absorption of tryptophan in the intestine, which reduces levels of tryptophan in the blood and leads to depression. High corn or other tryptophan-deficient diets can cause pellagra, which is a niacin-tryptophan deficiency disease with symptoms of dermatitis, diarrhea, and dementia. Hartnup's disease is a disorder in which tryptophan and other amino acids are not absorbed properly. Symptoms of Hartnup's disease include skin rashes, difficulty coordinating movements (cerebellar ataxia), and psychiatric symptoms such as depression or psychosis. Tryptophan supplements may be useful for treating Hartnup's. Assessment of tryptophan deficiency is done through studying excretion of tryptophan metabolites in the urine or blood. Blood may be the most sensitive test because the amino acid tryptophan is transported in a unique way. Increased urination of tryptophan breakdown products (such as kynurenine) correlates with increased tryptophan degradation, which occurs with oral contraception, depression, mental retardation, hypertension, and anxiety states. The requirement for tryptophan and protein decreases with age. The minimum daily requirement for adults is 3 mg/kg/day or about 200 mg a day. There is 400 mg of tryptophan in a cup of wheat germ. A cup of low fat cottage cheese contains 300 mg of tryptophan and chicken and turkey contain up to 600 mg of tryptophan per pound (http://www.dcnutrition.com). Tryptophan plays a role in "feast-induced" drowsiness. Ingestion of a meal rich in carbohydrates triggers the release of insulin. Insulin, in turn, stimulates the uptake of large neutral branched-chain amino acids (BCAAs) into muscle, increasing the ratio of tryptophan to BCAA in the bloodstream. The increased tryptophan ratio reduces competition at the large neutral amino acid transporter (which transports both BCAAs and tryptophan), resulting in greater uptake of tryptophan across the blood-brain barrier into the cerebrospinal fluid (CSF). Once in the CSF, tryptophan is converted into serotonin and the resulting serotonin is further metabolized into melatonin by the pineal gland, which promotes sleep. Under certain situations, tryptophan can be a neurotoxin and a metabotoxin. A neurotoxin is a compound that causes damage to the brain and nerve tissues. A metabotoxin is an endogenously produced metabolite that causes adverse health effects at chronically high levels. Chronically high levels of tryptophan can be found in glutaric aciduria type I (glutaric acidemia type I or GA1). GA1 is an inherited disorder in which the body is unable to completely break down the amino acids lysine, hydroxylysine, and tryptophan. Babies with glutaric acidemia type I are often born with unusually large heads (macrocephaly). Affected individuals may also have difficulty moving and may experience spasms, jerking, rigidity or decreased muscle tone, and muscle weakness. High levels of tryptophan have also been implicated in eosinophilia-myalgia syndrome (EMS), an incurable and sometimes fatal flu-like neurological condition linked to the ingestion of large amounts of L-tryptophan. The risk of developing EMS increases with larger doses of tryptophan and increasing age. Some research suggests that certain genetic polymorphisms may be related to the development of EMS. The presence of eosinophilia is a core feature of EMS, along with unusually severe myalgia (muscle pain). It is thought that both tryptophan and certain unidentified tryptophan contaminants may contribute to EMS (PMID: 1763543). It has also been suggested that excessive tryptophan or elevation of its metabolites could play a role in amplifying some of the pathological features of EMS (PMID: 10721094). This pathological damage is further augmented by metabolites of the kynurenine pathway (a tryptophan degradation pathway).

Wikipedia
Wikipedia
Tryptophan (symbol Trp or W) is an α-amino acid that is used in the biosynthesis of proteins. Tryptophan contains an α-amino group, an α-carboxylic acid group, and a side chain indole, making it a polar molecule with a non-polar aromatic beta carbon substituent. Tryptophan is also a precursor to the neurotransmitter serotonin, the hormone melatonin, and vitamin B3. It is encoded by the codon UGG.
HMDB
HMDB

Tryptophan (Trp) or L-tryptophan is an alpha-amino acid. These are amino acids in which the amino group is attached to the carbon atom immediately adjacent to the carboxylate group (alpha carbon). Amino acids are organic compounds that contain amino (-NH2) and carboxyl (-COOH) functional groups, along with a side chain (R group) specific to each amino acid. L-tryptophan is one of 20 proteinogenic amino acids, i.e., the amino acids used in the biosynthesis of proteins. Tryptophan is found in all organisms ranging from bacteria to plants to animals. It is classified as a non-polar, uncharged (at physiological pH) aromatic amino acid. Tryptophan is an essential amino acid, meaning the body cannot synthesize it, and it must be obtained from the diet. The requirement for tryptophan and protein decreases with age. The minimum daily requirement for adults is 3 mg/kg/day or about 200 mg a day. There is 400 mg of tryptophan in a cup of wheat germ. A cup of low-fat cottage cheese contains 300 mg of tryptophan and chicken and turkey contain up to 600 mg of tryptophan per pound (http://www.dcnutrition.com). Tryptophan is particularly plentiful in chocolate, oats, dried dates, milk, yogurt, cottage cheese, red meat, eggs, fish, poultry, sesame, chickpeas, almonds, sunflower seeds, pumpkin seeds, buckwheat, spirulina, and peanuts. Tryptophan is the precursor of both serotonin and melatonin. Melatonin is a hormone that is produced by the pineal gland in animals, which regulates sleep and wakefulness. Serotonin is a brain neurotransmitter, platelet clotting factor, and neurohormone found in organs throughout the body. Metabolism of tryptophan into serotonin requires nutrients such as vitamin B6, niacin, and glutathione. Niacin (also known as vitamin B3) is an important metabolite of tryptophan. It is synthesized via kynurenine and quinolinic acids, which are products of tryptophan degradation. There are a number of conditions or diseases that are characterized by tryptophan deficiencies. For instance, fructose malabsorption causes improper absorption of tryptophan in the intestine, which reduces levels of tryptophan in the blood and leads to depression. High corn diets or other tryptophan-deficient diets can cause pellagra, which is a niacin-tryptophan deficiency disease with symptoms of dermatitis, diarrhea, and dementia. Hartnup's disease is a disorder in which tryptophan and other amino acids are not absorbed properly. Symptoms of Hartnup's disease include skin rashes, difficulty coordinating movements (cerebellar ataxia), and psychiatric symptoms such as depression or psychosis. Tryptophan supplements may be useful for treating Hartnup's disease. Assessment of tryptophan deficiency is done through studying excretion of tryptophan metabolites in the urine or blood. Blood may be the most sensitive test because the amino acid tryptophan is transported in a unique way. Increased urination of tryptophan breakdown products (such as kynurenine) correlates with increased tryptophan degradation, which occurs with oral contraception, depression, mental retardation, hypertension, and anxiety states. Tryptophan plays a role in "feast-induced" drowsiness. Ingestion of a meal rich in carbohydrates triggers the release of insulin. Insulin, in turn, stimulates the uptake of large neutral branched-chain amino acids (BCAAs) into muscle, increasing the ratio of tryptophan to BCAA in the bloodstream. The increased tryptophan ratio reduces competition at the large neutral amino acid transporter (which transports both BCAAs and tryptophan), resulting in greater uptake of tryptophan across the blood-brain barrier into the cerebrospinal fluid (CSF). Once in the CSF, tryptophan is converted into serotonin and the resulting serotonin is further metabolized into melatonin by the pineal gland, which promotes sleep. Because tryptophan is converted into 5-hydroxytryptophan (5-HTP) which is then converted into the neurotransmitter serotonin, it has been proposed that consumption of tryptophan or 5-HTP may improve depression symptoms by increasing the level of serotonin in the brain. Tryptophan is sold over the counter in the United States (after being banned to varying extents between 1989 and 2005) and the United Kingdom as a dietary supplement for use as an antidepressant, anxiolytic, and sleep aid. It is also marketed as a prescription drug in some European countries for the treatment of major depression. There is evidence that blood tryptophan levels are unlikely to be altered by changing the diet, but consuming purified tryptophan increases the serotonin level in the brain, whereas eating foods containing tryptophan does not. This is because the transport system that brings tryptophan across the blood-brain barrier also transports other amino acids which are contained in protein food sources. Under certain situations, tryptophan can be a neurotoxin and a metabotoxin. A neurotoxin is a compound that causes damage to the brain and nerve tissues. A metabotoxin is an endogenously produced metabolite that causes adverse health effects at chronically high levels. Chronically high levels of tryptophan can be found in glutaric aciduria type I (glutaric acidemia type I or GA1). GA1 is an inherited disorder in which the body is unable to completely break down the amino acids lysine, hydroxylysine, and tryptophan due to a deficiency of mitochondrial glutaryl-CoA dehydrogenase (EC 1.3.99.7, GCDH). Excessive levels of their intermediate breakdown products (e.g. glutaric acid, glutaryl-CoA, 3-hydroxyglutaric acid, glutaconic acid) can accumulate and cause damage to the brain (and also other organs), but particularly the basal ganglia. Babies with glutaric acidemia type I are often born with unusually large heads (macrocephaly). Other symptoms include spasticity (increased muscle tone/stiffness) and dystonia (involuntary muscle contractions resulting in abnormal movement or posture), but many affected individuals are asymptomatic. High levels of tryptophan have also been implicated in eosinophilia-myalgia syndrome (EMS), an incurable and sometimes fatal flu-like neurological condition linked to the ingestion of large amounts of L-tryptophan. The risk of developing EMS increases with larger doses of tryptophan and increasing age. Some research suggests that certain genetic polymorphisms may be related to the development of EMS. The presence of eosinophilia is a core feature of EMS, along with unusually severe myalgia (muscle pain). It is thought that both tryptophan and certain unidentified tryptophan contaminants may contribute to EMS (PMID: 1763543 ). It has also been suggested that excessive tryptophan or elevation of its metabolites could play a role in amplifying some of the pathological features of EMS (PMID: 10721094 ). This pathological damage is further augmented by metabolites of the kynurenine pathway (a tryptophan degradation pathway). Reduced levels of tryptophan in the blood are typically seen when individuals are fighting chronic infections, suffering from traumatic injuries (burns or wounds) or experiencing sepsis (PMID: 26309411). Tryptophan is mainly catabolized through the enzymatic activity of two enzymes: indoleamine-2,3-dioxygenase (IDO) 1 and IDO2, both of which are expressed widely in human tissues, and both of which are induced by interferon gamma (IFN-gamma or IFNG). IDO1 and IDO2 generate tryptophan catabolites such as kynurenine and kynurenic acid.  These tryptophan catabolites activate the aryl hydrocarbon receptor (AhR), which plays a key role immune regulation. The role of IDO1 and IDO2 is to effectively deplete tryptophan levels to starve infectious organisms (bacteria and parasites), thereby killing them or slowing their growth.  On the other hand, the AhR activation leads to a state of immunosuppression and is intended to serve as a brake on the immune (overexpression of IFNG and IL-1B) response to the infectious organisms.  Unfortunately, tryptophan starvation is often not effective against viruses or even all infectious microbes. As a result, this AhR activation by tryptophan catabolites can lead to a situation where viruses (or certain pathogens) continue to survive and multiply even while the immune system is effectively turning off. As a result, high levels of kynurenine and low levels of tryptophan (a high kynurenine to tryptophan ratio) can lead to or even be symptomatic of chronic viral or pathogenic infections or, at worse, sepsis and septic shock (PMID: 33338598; PMID: 21731667).

Tryptophan 2DTryptophan 3D
Synonyms
Synonyms
L-tryptophan(S)-Tryptophan
tryptophanTryptophane
73-22-3trofan
h-Trp-ohtryptacin
L-TryptophaneArdeytropin
Identifiers
Manual Xrefs
Related Amino acids
Related Amino Acids
Biological activity
1. Function
Protein synthesis: Trp is a constituent of practically all proteins and peptides synthesized in the body. Tryptophan-tRNA ligase (EC6.1.1.2) loads Trp onto a specific tRNA in an ATP/magnesium-dependent reaction
2. Function
Energy fuel: Eventually, most Trp is completely oxidized providing about 5.8 kcal/g. The proportion that is converted to dead-end products such as kynurenic acid or used for the synthesis of products with lower energy yield is insignificant.
3. Function
NAD synthesis: A small proportion of catabolized Trp (as well as tryptamine, 5-hydroxytryptophan, serotonin, and melatonin) gives rise to nicotinamide-containing compounds. Impaired absorption in Hartnup syndrome is associated with pellagra-like skin changes that are typical for niacin deficiency. The branch point is at the conversion of 2-amino-3-carboxymuconate semialdehyde. While most of this intermediate is enzymically decarboxylated, a small proportion undergoes spontaneous dehydration to quinolinic acid (pyridine-2,3-dicarboxylate). Nicotinate-nucleotide pyrophosphorylase (EC2.4.2.19) decarboxylates quinolinate and attaches a ribose phosphate moiety. Nicotinate-nucleotide adenylyltransferase (EC2.7.7.18) can then add adenosine phosphate. Amination by either of two NAD synthases (EC6.3.5.1 and EC6.3.1.5) then completes NAD synthesis. It is usually assumed that about one-sixtieth of the metabolized Trp goes to NAD synthesis (Horwitt et al., 1981).
4. Function
Serotonin synthesis: The two-step synthesis of serotonin from Trp takes place in pinealocytes (in the pineal gland), raphe neurons of the brain, beta cells of the islets of Langerhans, enterochromaffin cells of the pancreas and small intestine, mast cells, and mononuclear leukocytes and requires biopterin and vitamin B6. Serotonin is an important neurotransmitter in the brain (serotonergic system) and a hormone-like substance in other tissues. Several synaptic receptors initiate neuron depolarization upon binding serotonin. Modulation of serotonin reuptake is an important drug target for the treatment of mood disorders, as well as appetite control.
5. Function
Melatonin synthesis: Serotonin serves as the precursor for melatonin (N-acetyl-5-methoxytryptamine) synthesis in the pineal gland, other brain regions, the retina, and the small intestine (Zagajewski et al., 2012). Synthesis proceeds in two steps that depend on adequate supplies of methionine, folate, and vitamin B12. Serotonin enters pinealocytes through the Na+- and Cl−-dependent transporter SLC6A4, whose activity appears to increase at night (Lima and Schmeer, 1994). Serotonin is then acetylated by aralkylamine N-acetyltransferase (EC2.3.1.87) and methylated by acetylserotonin O-methyltransferase (EC2.1.1.4). Melatonin participates in the regulation of circadian (Hebert et al., 1999) and seasonal rhythms (Pevet, 2000), influences growth hormone and thyroid hormone status (Meeking et al., 1999), increases pigmentation (Iyengar, 2000), promotes immune function (Guerrero et al., 2000), and may contribute to free radical scavenging (Karbownik et al., 2000). Intake as a dietary supplement may help to promote sleep-cycle adjustment and reducing the impact of time-zone shifts (jet lag, Wyatt et al. 2006)
6. Function
Photoprotection: Human lens epithelial cells produce 3-hydroxykynurenine glycoside. This pigment absorbs shortwave light and thereby appears to help protect the eye from ultraviolet (UV)–induced photodamage (Wood and Truscott, 1993)
7. Function
An essential amino acid; Used in biochemical research; (Merck Index) Used as a nutritional supplement for foods; (FDA) Used as a dietary supplement, for research, cereal enrichment, and as a medication; (HSDB) Permitted for use as an inert ingredient in non-food pesticide products; [EPA]
8. Function
Probe for studying protein structure and dynamics
9. Function
Tryptophan may be useful in increasing serotonin production, promoting healthy sleep, managing depression by enhancing mental and emotional well-being, managing pain tolerance, and managing weight.
References
1. Kohlmeier, M. (2015). Nutrient metabolism: Structures, functions, and genes (2nd Edition). Academic Press. 10.1016/C2010-0-64980-7
2. Merck Index - O'Neil MJ, Heckelman PE, Dobbelaar PH, Roman KJ (eds). The Merck Index, An Encyclopedia of Chemicals, Drugs, and Biologicals, 15th Ed. Cambridge, UK: The Royal Society of Chemistry, 2013 / (HSDB)
3. O'Neil, M.J. (ed.). The Merck Index - An Encyclopedia of Chemicals, Drugs, and Biologicals. Whitehouse Station, NJ: Merck and Co., Inc., 2006., p. 1683
4. Toxin and Toxin Target Database (T3DB) / (HSDB)
1. Biosynthesis: Tryptophan Biosynthesis
Tryptophan biosynthesis is a metabolic pathway that produces the essential amino acid tryptophan from chorismate, an intermediate in the shikimate pathway. Tryptophan is an important precursor for various biomolecules, including proteins, serotonin, and auxins. This pathway is present in plants, bacteria, and fungi but absent in animals, making tryptophan an essential amino acid that must be obtained from dietary sources in animals.

Anthranilate Synthase Reaction

The first committed step in tryptophan biosynthesis is catalyzed by anthranilate synthase, which converts chorismate to anthranilate.

Chorismate + Glutamine → Anthranilate + Glutamate

Anthranilate Phosphoribosyltransferase Reaction

Anthranilate phosphoribosyltransferase catalyzes the transfer of a phosphoribosyl group from 5-phosphoribosyl-1-pyrophosphate (PRPP) to anthranilate, forming N-(5'-phosphoribosyl)-anthranilate.

Anthranilate + PRPP → N-(5'-phosphoribosyl)-anthranilate + Pyrophosphate

Phosphoribosylanthranilate Isomerase Reaction

Phosphoribosylanthranilate isomerase catalyzes the isomerization of N-(5'-phosphoribosyl)-anthranilate to 1-(2-carboxyphenylamino)-1-deoxy-D-ribulose 5-phosphate.

N-(5'-phosphoribosyl)-anthranilate → 1-(2-carboxyphenylamino)-1-deoxy-D-ribulose 5-phosphate

Indole-3-glycerol Phosphate Synthase Reaction

Indole-3-glycerol phosphate synthase catalyzes the conversion of 1-(2-carboxyphenylamino)-1-deoxy-D-ribulose 5-phosphate to indole-3-glycerol phosphate, releasing carbon dioxide.

1-(2-carboxyphenylamino)-1-deoxy-D-ribulose 5-phosphate → Indole-3-glycerol phosphate + CO 2

Indole-3-glycerol Phosphate Aldolase Reaction

Indole-3-glycerol phosphate aldolase catalyzes the conversion of indole-3-glycerol phosphate to indole and D-glyceraldehyde 3-phosphate.

Indole-3-glycerol phosphate → Indole + D-glyceraldehyde 3-phosphate

Tryptophan Synthase Reaction

Tryptophan synthase catalyzes the final step, where indole is condensed with serine to form tryptophan.

Indole + L-Serine → L-Tryptophan + H 2 O

1. Industrial manufacturing
Fermentation of natural or biologically available substances with Corynebacterium glutamicum; enzymatically from indole, pyruvic acid, and ammonia using microbial tryptophanase
SRI / Hazardous Substances Data Bank (HSDB)
2. Industrial manufacturing
Synthesis starting with beta-indolylaldehyde and hippuric acid; ... from hydantoin; alternate route starting with 3-indoleacetonitrile.
Budavari, S. (ed.). The Merck Index - Encyclopedia of Chemicals, Drugs and Biologicals. Rahway, NJ: Merck and Co., Inc., 1989., p. 1540 / Hazardous Substances Data Bank (HSDB)
Sources
Dietary Sources
Natural Sources
Commercial Sources

Can be produced commercially through enzymatic or chemical synthesis methods

Metabolism

Kohlmeier, M. (2015)

Human Metabolism

Trp can be converted into very different components depending on location and regulation. While most Trp is eventually broken down into carbon dioxide, water, and urea, intermediary or alternative products of biological importance include alanine, acetyl-CoA, serotonin, melatonin, NAD, and NADP. It should also be noted that the minor metabolite kynurenic acid is a potent antagonist of excitatory N-methyl-d-aspartate receptors of brain neurons, while quinolinate is a potent agonist of these same receptors (Luthman, 2000). The precise balance of the alternative Trp degradation reactions in the brain is likely to be of great physiological importance and may be amenable to pharmacological modulation. In specific instances, genetic variants affecting Trp metabolism may promote the development of epileptic seizures and other pathologies. Catabolism: Complete oxidation of Trp to l-alanine and two acetyl-CoA molecules proceeds in 11 steps, followed by one cycle of beta-oxidation (of crotonyl CoA), and depends on thiamin, riboflavin, vitamin B6, niacin, pantothenate, lipoate, ubiquinone, magnesium, and iron. The heme-enzyme tryptophan 2,3-dioxygenase (EC1.13.11.11) opens the pyrrole ring of Trp, but also of d-tryptophan, 5-hydroxytryptophan, tryptamine, and 5-HT (serotonin). Indoleamine-pyrrole 2,3-dioxygenase (EC1.13.11.42), which does the same, has slightly different substrate specificity and tissue expression pattern. Alternatively, the PLP-dependent enzyme tryptophan aminotransferase (EC2.6.1.27) can deaminate Trp; the fate of the resulting indole 3-pyruvate is uncertain, but it may also undergo ring opening and rejoin the main catabolic pathway. Arylformamidase (EC3.5.1.9) generates kynurenine by hydrolyzing N-formylkynurenine. Most kynurenine is then oxidized by the flavoenzyme kynurenine 3-monooxygenase (EC1.14.13.9). Two quantitatively minor alternative reactions also occur. One is the irreversible transamination, which is dependent on PLP, to kynurenic acid (4-(2-aminophenyl)-2,4-dioxobutanoate). Kynurenine-glyoxylate aminotransferase (EC2.6.1.63), aromatic-amino-acid-glyoxylate aminotransferase (EC2.6.1.60), or kynurenine-oxoglutarate aminotransferase (KAT, EC2.6.1.7) can catalyze this reaction. Two genetically distinct forms of the latter enzyme, KATI and KATII, occur in many tissues, including the liver, kidneys, and brain. Kynurenic acid is a potent inhibitor of all three known ionotropic excitatory amino acid receptors, including the NMDA receptor. Another minor reaction is the premature cleavage by PLP-dependent kynureninase (EC3.7.1.3), which releases anthralinate and l-alanine. Both kynurenic acid and anthralinate are dead-end products that can be excreted after glucuronidation. The preferred reaction of kynureninase, however, is the hydrolysis of 3-hydroxy-kynurenine to 3-hydroxyanthralinate and l-alanine. The alternatively possible transamination of 3-hydroxy-kynurenine by kynurenine-oxoglutarate aminotransferase (EC2.6.1.7) to xanthurenic acid is insignificant so long as kynureninase activity is normal. Oxidative cleavage of 3-hydroxy-anthralinate by the iron-enzyme 3-hydroxyanthranilate 3,4-dioxygenase (EC1.13.11.6) generates 2-amino-3-carboxymuconate semialdehyde. This is the branch point for nicotinate synthesis, since a small percentage of it spontaneously rearranges to the NAD precursor quinolinic acid. The bulk of 2-amino-3-carboxymuconate semialdehyde is decarboxylated by aminocarboxymuconate-semialdehyde decarboxylase (EC4.1.1.45). Some of the product, 2-amino-muconate semialdehyde (2-amino-3-(3-oxoprop-2-enyl)-but-2-enedioate), may rearrange nonenzymically to picolinate. Most of it, however, is oxidized to 2-aminomuconate by aminomuconate-semialdehyde dehydrogenase (EC1.2.1.32) and then reduced again to 2-oxoadipate by an as-yet unknown enzyme. In exchange for alpha-ketoglutarate, the oxodicarboxylate carrier (Fiermonte et al., 2001) transports 2-oxoadipate, an intermediate of lysine catabolism, across the inner mitochondrial membrane. Continued catabolism to acetyl-CoA takes place at the mitochondrial matrix. An enzyme complex whose identity is not entirely clear catalyzes the oxidative phosphorylation and conjugation to CoA. The oxoglutarate dehydrogenase (EC1.2.4.2) complex is able to facilitate the reaction (Bunik and Pavlova, 1997), but the existence of a closely related 2-oxoadipate dehydrogenase has not been ruled out. The alpha-ketoglutarate dehydrogenase complex contains thiamin pyrophosphate (bound to the El subunits), and lipoic acid (bound to the E2 subunits); a third type of subunit, dihydrolipoamide dehydrogenase (E3, EC1.8.1.4), then uses covalently bound FAD to reduce NAD. The resulting glutaryl-CoA is oxidized and decarboxylated by glutaryl-CoA dehydrogenase (EC1.3.99.7), which contains covalently bound FAD. Crotonyl-CoA completes beta-oxidation to 2 moles of acetyl-CoA. The three successive steps are catalyzed by mitochondrial enoyl-CoA hydratase (EC4.2.1.17), mitochondrial short-chain 3-hydroxyacyl-CoA dehydrogenase (EC1.1.1.35), and mitochondrial acetyl-CoA C-acyltransferase (3-ketoacyl-CoA thiolase, EC2.3.1.16). Most 5-HT and some tryptamine are normally metabolized by monoamine oxidase A (MAOA, EC1.4.3.4) and one or more of the aldehyde dehydrogenases (ALDH, EC1.2.1.3/NAD-requiring, EC1.2.1.4/NADP-requiring, and EC1.2.1.5/NAD or NADP-requiring); 5-HT is converted into 5-hydroxyindole-3-acetate and tryptamine into indole-3-acetate. Both 5-HT and tryptamine can also be shunted into the main Trp catabolic pathway by tryptophan 2,3-dioxygenase (EC1.13.11.11, see previous discussion). Some 5-HT can also be converted by alcohol dehydrogenase (EC1.1.1.1) into the dead-end product 5-hydroxytryptophol (5-HTOL), which has biological effects similar to 5-HT. Ethanol acutely increases the proportion converted into 5-HTOL. A single dose of ethanol (one liter of beer in a 70 kg man) ingested with several bananas was enough to cause headaches, diarrhea, and fatigue in healthy subjects (Helander and Some, 2000).

L-Tryptophan + O 2 + H 2 O ⇌ N-Formylkynurenine
L-Tryptophan undergoes oxidative cleavage by tryptophan 2,3-dioxygenase (EC 1.13.11.11) to form N-formylkynurenine.
N-Formylkynurenine + H 2 O ⇌ Kynurenine + Formate
N-Formylkynurenine is hydrolyzed by arylformamidase (EC 3.5.1.9) to produce kynurenine and formate.
Kynurenine + O 2 + NADPH ⇌ 3-Hydroxykynurenine + H 2 O + NADP +
Kynurenine is oxidized by kynurenine 3-monooxygenase (EC 1.14.13.9) in the presence of oxygen and NADPH, producing 3-hydroxykynurenine, water, and NADP+.
3-Hydroxykynurenine + H 2 O ⇌ 3-Hydroxyanthranilate + L-Alanine
3-Hydroxykynurenine is hydrolyzed by kynureninase (EC 3.7.1.3) to produce 3-hydroxyanthranilate and L-alanine.
3-Hydroxyanthranilate + O 2 ⇌ 2-Amino-3-carboxymuconate semialdehyde
3-Hydroxyanthranilate undergoes oxidative cleavage by 3-hydroxyanthranilate 3,4-dioxygenase (EC 1.13.11.6) to form 2-amino-3-carboxymuconate semialdehyde.
2-Amino-3-carboxymuconate semialdehyde ⇌ Quinolinic acid
A small percentage of 2-amino-3-carboxymuconate semialdehyde spontaneously rearranges to form quinolinic acid, a precursor for NAD synthesis.
2-Amino-3-carboxymuconate semialdehyde ⇌ 2-Aminomuconate semialdehyde + CO 2
2-Amino-3-carboxymuconate semialdehyde is decarboxylated by aminocarboxymuconate-semialdehyde decarboxylase (EC 4.1.1.45) to produce 2-aminomuconate semialdehyde and carbon dioxide.
2-Aminomuconate semialdehyde + NAD + + H 2 O ⇌ 2-Aminomuconate + NADH + H +
2-Aminomuconate semialdehyde is oxidized by aminomuconate-semialdehyde dehydrogenase (EC 1.2.1.32) to form 2-aminomuconate, NADH, and hydrogen ion.
2-Aminomuconate ⇌ 2-Oxoadipate
2-Aminomuconate undergoes a reduction reaction by an unknown enzyme to form 2-oxoadipate.
2-Oxoadipate + CoA + NAD + ⇌ Glutaryl-CoA + CO 2 + NADH
2-Oxoadipate is decarboxylated and conjugated with CoA by the oxoglutarate dehydrogenase complex (EC 1.2.4.2), producing glutaryl-CoA, carbon dioxide, and NADH.
Glutaryl-CoA + FAD ⇌ Crotonyl-CoA + FADH 2 + CO 2
Glutaryl-CoA is oxidized and decarboxylated by glutaryl-CoA dehydrogenase (EC 1.3.99.7) to form crotonyl-CoA, FADH2, and carbon dioxide.
Crotonyl-CoA + H 2 O ⇌ 3-Hydroxybutyryl-CoA
Crotonyl-CoA is hydrated by enoyl-CoA hydratase (EC 4.2.1.17) to produce 3-hydroxybutyryl-CoA.
3-Hydroxybutyryl-CoA + NAD + ⇌ Acetoacetyl-CoA + NADH
3-Hydroxybutyryl-CoA is oxidized by short-chain 3-hydroxyacyl-CoA dehydrogenase (EC 1.1.1.35) to produce acetoacetyl-CoA and NADH.
Acetoacetyl-CoA ⇌ 2 Acetyl-CoA
Acetoacetyl-CoA is cleaved by acetyl-CoA C-acyltransferase (EC 2.3.1.16) to form two molecules of acetyl-CoA.
Kohlmeier, M. (2015). Nutrient metabolism: Structures, functions, and genes (2nd Edition). Academic Press. 10.1016/C2010-0-64980-7

Homo sapiens

This pathway depicts the metabolic reactions and pathways associated with tryptophan metabolism in animals. Tryptophan is an essential amino acid. This means that it cannot be synthesized by humans and other mammals and therefore must be part of the diet. Unlike animals, plants and microbes can synthesize tryptophan from shikimic acid or anthranilate. As one of the 20 proteogenic amino acids, tryptophan plays an important role in protein biosynthesis through the action of tryptophanyl-tRNA synthetase. As shown in this pathway, tryptophan can be linked to the tryptophanyl-tRNA via either the mitochondrial or cytoplasmic tryptophan tRNA ligases. Also shown in this pathway map is the conversion of tryptophan to serotonin (a neurotransmitter). In this process, tryptophan is acted upon by the enzyme tryptophan hydroxylase, which produces 5-hydroxytryptophan (5HTP). 5HTP is then converted into serotonin (5-HT) via aromatic amino acid decarboxylase. Serotonin, in turn, can be converted into N-acetyl serotonin (via serotonin-N-acetyltransferase) and then melatonin (a neurohormone), via 5-hydroxyindole-O-methyltransferase. The melatonin can be converted into 6-hydroxymelatonin via the action of cytochrome P450s in the endoplasmic reticulum. Serotonin has other fates as well. As depicted in this pathway it can be converted into N-methylserotonin via Indolethylamine-N-methyltransferase (INMT) or it can be converted into formyl-5-hydroxykynurenamine via indoleamine 2,3-dioxygenase. Serotonin may also be converted into 5-methoxyindoleacetate via a series of intermediates including 5-hydroxyindoleacetaldehyde and 5-hydroxyindoleacetic acid. Tryptophan can be converted or broken down into many other compounds as well. It can be converted into tryptamine via the action of aromatic amino acid decarboxylase. The resulting tryptamine can then be converted into indoleacetaldehyde via kynurenine 3-monooxygenase and then into indoleacetic acid via the action of aldehyde dehydrogenase. Tryptophan also leads to the production of a very important compound known as kynurenine. Kynurenine is synthesized via the action of tryptophan 2,3-dioxygnase, which produces N-formylkynurenine. This compound is converted into kynurenine via the enzyme known as kynurenine formamidase (AFMID). Kynurenine has at least 3 fates. First, kynurenine can undergo deamination in a standard transamination reaction yielding kynurenic acid. Secondly, kynurenine can undergo a series of catabolic reactions (involving kynureninase and kynurenine 3-monooxygenase) producing 3-hydroxyanthranilate plus alanine. In this reaction, kynureninase catabolizes the conversion of kynurenine into anthranilic acid while kynurenine—oxoglutarate transaminase (also known as kynurenine aminotransferase or glutamine transaminase K, GTK) catabolizes its conversion into kynurenic acid. The action of kynurenine 3-hydroxylase on kynurenic acid leads to 3-hydroxykynurenine. The oxidation of 3-hydroxyanthranilate converts it into 2-amino-3-carboxymuconic 6-semialdehyde, which has two fates. It can either degrade to form acetoacetate or it can cyclize to form quinolate. Most of the body’s 3-hydroxyanthranilate leads to the production of acetoacetate (a ketone body), which is why tryptophan is also known as a ketogenic amino acid. An important side reaction in the liver involves a non-enzymatic cyclization into quinolate followed by transamination and several rearrangements to yield limited amounts of nicotinic acid, which leads to the production of a small amount of NAD+ and NADP+.

Biochemical reactions
Bioactivity and Pharmacokinetics
DrugBank

Tryptophan is critical for the production of the body's proteins, enzymes and muscle tissue. It is also essential for the production of niacin, the synthesis of the neurotransmitter serotonin and melatonin. Tryptophan supplements can be used as natural relaxants to help relieve insomnia. Tryptophan can also reduce anxiety and depression and has been shown to reduce the intensity of migraine headaches. Other promising indications include the relief of chronic pain, reduction of impulsivity or mania and the treatment of obsessive or compulsive disorders. Tryptophan also appears to help the immune system and can reduce the risk of cardiac spasms. Tryptophan deficiencies may lead to coronary artery spasms. Tryptophan is used as an essential nutrient in infant formulas and intravenous feeding. Tryptophan is marketed as a prescription drug (Tryptan) for those who do not seem to respond well to conventional antidepressants. It may also be used to treat those afflicted with seasonal affective disorder (a winter-onset depression). Tryptopan serves as the precursor for the synthesis of serotonin (5-hydroxytryptamine, 5-HT) and melatonin (N-acetyl-5-methoxytryptamine).

T3DB Mechanism of Action

A number of important side reactions occur during the catabolism of tryptophan on the pathway to acetoacetate. The first enzyme of the catabolic pathway is an iron porphyrin oxygenase that opens the indole ring. The latter enzyme is highly inducible, its concentration rising almost 10-fold on a diet high in tryptophan. Kynurenine is the first key branch point intermediate in the pathway. Kynurenine undergoes deamniation in a standard transamination reaction yielding kynurenic acid. Kynurenic acid and metabolites have been shown to act as antiexcitotoxics and anticonvulsives. A second side branch reaction produces anthranilic acid plus alanine. Another equivalent of alanine is produced further along the main catabolic pathway, and it is the production of these alanine residues that allows tryptophan to be classified among the glucogenic and ketogenic amino acids. The second important branch point converts kynurenine into 2-amino-3-carboxymuconic semialdehyde, which has two fates. The main flow of carbon elements from this intermediate is to glutarate. An important side reaction in liver is a transamination and several rearrangements to produce limited amounts of nicotinic acid, which leads to production of a small amount of NAD<sup>+</sup> and NADP<sup>+</sup>.

Cellular Locations
Tissue Locations
1. Adsorption
Mastication of foods in the mouth, denaturation by hydrochloric acid, and unspecific protein hydrolysis by pepsin in the stomach initiate the breakdown of Trp-containing proteins (Figure 8.40). Pancreatic proteases and aminopeptidases on the intestinal brush border membrane can then generate free Trp, as well as dipeptides and tripeptides, which are suitable for absorption. Dipeptides and tripeptides are taken up via the proton-peptide cotransporter (SLC15A1, PepT1). The sodium–amino acid cotransport system B° is the main conduit for the intestinal uptake of free Trp (Avissar et al., 2001); the molecular defect responsible for impaired uptake (and increased renal losses due to diminished recovery) in Hartnup disease is due to defective B°AT1 (SLC6A19), which is one of the B° transporters. Exchange for other neutral amino acids via the sodium-independent transporter complex BAT1-rBAT (SLC7A9- SLC3A1) augments this pathway (Verrey et al., 1999; Mizoguchi et al., 2001). The T-type amino acid transporter 1 (TAT1, SLC16A10) facilitates ion-independent diffusion across the basolateral membrane of enterocytes in the jejunum, ileum, and colon (Ramadan et al., 2007). Additional transport capacity is provided by the 4F2-glycoprotein-anchored exchanger LAT2 (Rossier et al., 1999; Rajan et al., 2000).
Kohlmeier, M. (2015). Nutrient metabolism: Structures, functions, and genes (2nd Edition). Academic Press. 10.1016/C2010-0-64980-7
1. Distribution
Blood circulation: The plasma concentration of Trp (typically around 50µmol/l) decreases in response to low dietary intake (Kaye et al., 2000). Uptake from the blood into tissues uses various transporters, including system T (TAT1), LAT1, and LAT2, whose expression patterns vary considerably between specific tissues. BBB: The sodium-independent transporter TAT1 and the glycoprotein anchored complex LAT1 are expressed in brain capillary endothelial cells and certainly contribute to Trp transport, but their relative importance, location, and the role of other transporters are not completely understood. Trp competes with the BCAAs (valine, leucine, and isoleucine) and other large neutral amino acids (methionine, tyrosine, tryptophan, and histidine) for transport into the brain. This may mean that increased blood concentrations of phenylalanine (especially in patients with PKU, an inborn error of metabolism with defective phenylalanine utilization) or BCAAs (due to a high-carbohydrate diet) limit Trp availability in the brain. Materno-feta/transfer: The exchanger LAT1 appears to be the major route for Trp traveling from maternal blood into the syncytiotrophoblast (Ritchie and Taylor, 2001). Transfer across the basolateral membrane may proceed predominantly via LAT1 and LAT2 (Ritchie and Taylor, 2001); a contribution by TAT1, which is strongly expressed in the placenta (Kim et al., 2001), has been disputed (Ritchie and Taylor, 2001)
Kohlmeier, M. (2015). Nutrient metabolism: Structures, functions, and genes (2nd Edition). Academic Press. 10.1016/C2010-0-64980-7
1. Excretion
Due to very effective renal reabsorption of filtered Trp very little is lost with urine. Uptake from the proximal tubular lumen uses mainly the sodium-dependent system B° (Avissar et al., 2001), and is augmented by the action of the sodium-independent transporter complexes bo,+ and BAT1-rBAT (Verrey et al., 1999). Impaired reabsorption in Hartnup disease, due to defective system B°AT1 (SLC1A4) causes excessive renal losses. Minor Trp metabolites in urine include 5-hydroxyindoleacetic acid, from serotonin breakdown, and 2-(alpha-mannopyranosyl)-1-tryptophan, from a pathway involving mannosylation of Trp (Gutsche et al., 1999).
Kohlmeier, M. (2015). Nutrient metabolism: Structures, functions, and genes (2nd Edition). Academic Press. 10.1016/C2010-0-64980-7
1. Regulation
High tissue concentration of Trp stabilizes tryptophan 2,3-dioxygenase (EC1.13.11.11), thereby promoting Trp breakdown. A carbohydrate-rich, protein-poor diet aids in the retention of Trp in the brain (Kaye et al., 2000). Enhanced tryptophan catabolism through selective upregulation of indoleaminepyrrole 2,3-dioxygenase (EC1.13.11.42) expression in trophoblasts and macrophages appears to suppress T-cell activity and contribute in a critical way to the immune tolerance of genetically different fetal tissues during pregnancy (Munn et al., 1998)
Kohlmeier, M. (2015). Nutrient metabolism: Structures, functions, and genes (2nd Edition). Academic Press. 10.1016/C2010-0-64980-7
Predicted Properties
Safety and Hazards
eCFR

(a) Product NIL (b) Conditions of use NIL

NIL
Hazard Idientification

Information pertaining to Adverse Effects in (1) Animals and (2) Humans

'10 Protein and Amino Acids.' Institute of Medicine. 2005. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington, DC: The National Academies Press. doi: 10.17226/10490.
Targets and transporters
Annotations
Tryptophan and indole metabolism in immune regulation

L-tryptophan is an essential amino acid that undergoes complex metabolic routes, resulting in production of many types of signaling molecules that fall into two types: retaining the indole ring such as serotonin, melatonin and indole-pyruvate or breaking the indole ring to form kynurenine. Kynurenines are the precursor of signaling molecules and are the first step in de novo NAD+ synthesis. In mammalian cells, the kynurenine pathway is initiated by the rate-limiting enzymes tryptophan-2,3-dioxygenase (TDO) and interferon responsive indoleamine 2,3-dioxygenase (IDO1) and is the major route for tryptophan catabolism. IDO1 regulates immune cell function through the kynurenine pathway but also by depleting tryptophan in microenvironments, and especially in tumors, which led to the development of IDO1 inhibitors for cancer therapy. However, the connections between tryptophan depletion versus product supply remain an ongoing challenge in cellular biochemistry and metabolism. Here, we highlight current knowledge about the physiological and pathological roles of tryptophan signaling network with a focus on the immune system.

1. Fiore A, Murray PJ. Tryptophan and indole metabolism in immune regulation. Curr Opin Immunol. 2021;70:7-14. doi: 10.1016/j.coi.2020.12.001
Effect of L-tryptophan supplementation on exercise performance

The performance of strenuous physical exercise is associated with discomfort and pain, the tolerance for that being modulated by the activity of the endogenous opioid systems. As 5-hydroxy-tryptamine (5-HT) affects nociception through its effects on the enkephalin-endorphin system, we have analyzed the effects of a moderate supplementation with L-tryptophan, the immediate precursor of 5-HT, on endurance and sensation of effort. Twelve healthy sportsmen were subjected to a work load corresponding to 80% of their maximal oxygen uptake on two separate trials, after receiving a placebo and after receiving the same amount of L-tryptophan. The subjects ran on a treadmill until exhaustion. Total exercise time, perceived exertion rate, maximum heart rate, peak oxygen consumption, pulse recovery rate, and excess post-exercise oxygen consumption were determined during the two trials. The total exercise time was 49.4% greater after receiving L-tryptophan than after receiving the placebo. A lower rate of perceived exertion was exhibited by the group while on tryptophan although the differences from the control group were not statistically significant. No differences were observed in the other parameters between the two trials. The longer exercise time als well at the total work load performed could be due to an increased pain tolerance as a result of L-tryptophan ingestion.

1. Segura R, Ventura JL. Effect of L-tryptophan supplementation on exercise performance. Int J Sports Med. 1988;9(5):301-305. doi:10.1055/s-2007-1025027
Tryptophan supplementation induces a positive bias in the processing of emotional material...

Rationale: The serotonin precursor L-tryptophan (TRP) is available as a nutritional supplement and is licensed as an antidepressant in a number of countries. However, evidence of its efficacy as the primary treatment for depression is limited, and the direct action of TRP on the symptoms of depression and anxiety has not been well-characterised. Objectives: The present study assessed whether TRP induces cognitive changes opposite to the negative biases found in depression and characteristic of those induced by serotonergic antidepressants in healthy volunteers. Materials and methods: Thirty eight healthy volunteers were randomised to receive 14 days double-blind intervention with TRP (1 g 3x a day) or placebo. On the final day, emotional processing was assessed using four tasks: facial expression recognition, emotion-potentiated startle, attentional probe and emotional categorisation and memory. Results: TRP increased the recognition of happy facial expressions and decreased the recognition of disgusted facial expressions in female, but not male, volunteers. TRP also reduced attentional vigilance towards negative words and decreased baseline startle responsivity in the females. Conclusions: These findings provide evidence that TRP supplementation in women induces a positive bias in the processing of emotional material that is reminiscent of the actions of serotonergic antidepressants. This highlights a key role for serotonin in emotional processing and lends support to the use of TRP as a nutritional supplement in people with mild depression or for prevention in those at risk. Future studies are needed to clarify the effect of tryptophan on these measures in men.

1. Murphy, Susannah E et al. “Tryptophan supplementation induces a positive bias in the processing of emotional material in healthy female volunteers.” Psychopharmacology vol. 187,1 (2006): 121-30. doi:10.1007/s00213-006-0401-8
Effects of L-tryptophan on sleepiness and on sleep

Over the past 20 yr, 40 controlled studies have been described concerning the effects of L-tryptophan on human sleepiness and/or sleep. The weight of evidence indicates that L-tryptophan in doses of 1 g or more produces an increase in rated subjective sleepiness and a decrease in sleep latency (time to sleep). There are less firm data suggesting that L-tryptophan may have additional effects such as decrease in total wakefulness and/or increase in sleep time. Best results (in terms of positive effects on sleep or sleepiness) have been found in subjects with mild insomnia, or in normal subjects reporting a longer-than-average sleep latency. Mixed or negative results occur in entirely normal subjects--who are not appropriate subjects since there is 'no room for improvement'. Mixed results are also reported in severe insomniacs and in patients with serious medical or psychiatric illness.

1. Hartmann E. Effects of L-tryptophan on sleepiness and on sleep. J Psychiatr Res. 1982;17(2):107-113. doi: 10.1016/0022-3956(82)90012-7
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AminoADB (Amino Acid Database). (2025). AminoADB Compound Summary for AADB0018, Tryptophan. Retrieved March 17, 2025 from https://aminoadb.org/aminoacid/tryptophan.php.