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Related to tryptophan: L-tryptophan


a naturally occurring amino acid, one of the essential amino acids; it is a precursor of serotonin. Adequate levels in the diet may mitigate pellagra by compensating for deficiencies of niacin.

tryp·to·phan (Trp, W),

2-Amino-3-(3-indolyl)propionic acid; the l-isomer is a component of proteins; a nutritionally essential amino acid.


/tryp·to·phan/ (Trp) (W) (trip´to-fan) a naturally occurring amino acid, existing in proteins and essential for human metabolism. It is a precursor of serotonin. Adequate levels may mitigate pellagra by compensating for deficiencies of niacin.


(trĭp′tə-făn′) also


An essential amino acid, C11H12N2O2, formed from proteins during digestion by the action of proteolytic enzymes. It is necessary for normal growth and development and is the precursor of several substances, including serotonin and niacin.

tryptophan (Trp)

an amino acid essential for normal growth and nitrogen balance. Tryptophan is the precursor of several important biomolecules, including serotonin and niacin. See also amino acid, protein.
enlarge picture
Chemical structure of tryptophan


An essential amino acid, which is a key building block in protein biosynthesis. It is a precursor for serotonin (a neurotransmitter) and niacin (a B vitamin).

Dietary sources
Milk, sesame seeds, soy beans, spirulina, sunflower seeds, cashews.
Fringe nutrition
Tryptophan has been promoted for its alleged ability to induce sleep, and as an antidepressint.


(W) (trip'tŏ-fan)
A nutritionally essential amino acid; the l-isomer is a component of proteins.


An antidepressant drug. L-tryptophan, sold in USA as a non-prescription food additive was withdrawn by the American Food and Drugs Administration (FDA) because of reports of a severe muscle disorder apparently caused by an unidentified contaminant. It is used only by hospital specialists who are aware of the risks. A brand name is Optimax.
Tryptophanclick for a larger image
Fig. 306 Tryptophan . Molecular structure.

tryptophan (W, Trp)

one of 20 AMINO ACIDS common in protein. It has a nonpolar ‘R’ group structure and is relatively insoluble in water. See Fig. 306 . The ISOELECTRIC POINT of tryptophan is 5.9.


An essential amino acid that has to consumed in the diet because it cannot be manufactured by the body. Tryptophan is converted by the body to niacin, one of the B vitamins.
Mentioned in: Hartnup Disease

amino acids

organic acids in which one or more of the hydrogen atoms is replaced by the amino group, NH2. They are the end-products of digestion of dietary protein and from them the body synthesizes its own proteins. Within the body amino acids also act as precursors of many other molecules essential for life. Amino acids may be categorized as essential or non-essential. essential amino acids: those that must be provided in the diet since the human body does not have the enzymes for their synthesis; of the 20 amino acids that are present in proteins or as free amino acids in the body, nine are 'essential' (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine). Of these, three are known as branched-chain aminoacids (BCAA): leucine is oxidized to a significant extent during exercise, and tracer studies that follow leucine kinetics are often used as an estimation of protein turnover; isoleucine and valine can also serve as fuel sources. It has been claimed that ingestion of BCAA before and during exercise may improve the physiological and psychological responses, and that BCAA with arginine and/or other amino acids may promote growth hormone release, but other studies do not support this. There are no known toxic effects. See also ergogenic aids, gluconeogenesis; Table 1.
Table 1: Ergogenic aids: supplements used by athletes
SubstanceDescriptionClaimed ergogenic effectSupporting evidence
With clear scientific evidence
CaffeineStimulant in coffee and tea
  • Benefits performance by improving alertness, concentration, reaction time.
  • Increases fat oxidation during endurance exercise.
Improves performance in most events, except very short high-intensity exercise; increases cognitive functioning during exercise.
CreatineCarrier of high-energy phosphates in muscleIncreases the energy reserve, improves strength, reduces fatigue, and increases protein synthesisIncreases intramuscular Cr and PCr; improves performance in repeated sprint bouts (and reported to do so after even a single bout); improves recovery between bouts (but response varies between individuals). Anabolic properties unclear.
  • Sodium bicarbonate
  • Sodium citrate
BuffersImproves high-intensity exercise performance by limiting decrease in pH in ECF as a whole and indirectly in muscle ICFLarge doses can improve performance
With mixed scientific evidence
Antioxidant nutrientsVitamins, especially C and EProvides protection against muscle damage by reducing oxidative stressBenefits established at cellular level; no detectable aid to performance
ArginineAmino acid in normal dietStimulates release of growth hormone, promoting gain in muscle mass and strengthSome evidence of GH promotion when combined with other amino acids (ornithine, lysine, BCAA); no conclusive evidence of effect when taken alone
Branched-chain amino acids (BCAA)Leucine, isoleucine and valine
  • Retards the development of central fatigue and so improves performance.
  • Improves efficiency of training
No good evidence of improved endurance performance. Evidence of accelerated recovery from muscle fatigue when given with other amino acids during eccentric exercise training
GlutamineAmide of amino acid glutamateMaintains a healthy immune system during training and improves muscle glycogen resynthesisDoes not affect immune function; possibly affects muscle glycogen resynthesis
GlycerolComponent of triacylglycerol moleculeInduces hyperhydration, decreases heat stress, and improves performanceDoes have the first two actions, but effects on performance are unclear
Lacking scientific support
AndrostenedioneSynthetic productIncreases testosterone and thus muscle mass and strength, and improves recoveryDoes not increase testosterone secretion; has no effect on strength
Hydroxy-methyl butyrate (HMB)Metabolite of the amino acid leucineEnhances gain in body mass and strength associated with resistance training, and improves recoveryPossible small effects only on lean body mass and strength
BoronMicronutrient present in vegetables and non-citrus fruitsIncreases testosterone levels, to improve bone density, muscle mass, and strengthImproves bone mineral density in postmenopausal women; no effect on bone density, muscle mass or strength in men
CarnitineSubstance important for fatty acid transport into mitochondriaImproves fat oxidation, helps weight lossNo supporting evidence
CholinePrecursor of acetylcholineImproves performance, decreases fatigue and enhances fat metabolismNo supporting evidence
Chromium (chromium picolinate)Micronutrient that potentiates insulin actionPromotes fat oxidation and muscle buildingNo supporting evidence
Coenzyme Q10Part of the electron transport chain in the mitochondriaImproves aerobic capacity and cardiovascular dynamicsNo supporting evidence
GinsengRoot of the Araliaceous plantImproves strength, performance, stamina, and cognitive functioning; reduces fatigueNo supporting evidence
InosineNucleoside found naturally in brewer's yeast and organ meatsIncreases ATP stores, improve strength, training quality, and performanceNo supporting evidence
Medium-chain triacylglycerols (MCT)Triglycerides containing fatty acids with a carbon chain length of 6-10Improves energy supply, reduces rate of muscle glycogen breakdown, and improves performanceNo supporting evidence
PyruvateEnd-product of aerobic glycolysisImproves endurance capacity and recovery; increases glycogen storageLimited supporting evidence
PolylactatePolymer of lactateProvides energyNo effects on performance
Wheat germ oilWheat embryo extractImproves enduranceNo supporting evidence


a monoamine (5-hydroxytryptamine, 5-HT) formed from the essential amino acid tryptophan. Its widespread actions include vasoconstriction, inhibition of gastric secretion and stimulation of smooth muscle. It is also an important neurotransmitter in the central nervous system; as such it is involved in pain transmission and perception, and can influence a variety of behaviours, including tiredness, sleep, mood and mental fatigue. It is suggested that an increased level of serotonin makes it mentally harder to maintain a steady pace of exercise, as in running or cycling ('central fatigue'). Administration of branched-chain amino acids has been claimed to reduce uptake of tryptophan by the brain and therefore to diminish serotonin production. See also ergogenic aids; appendix 4.4 .

tryptophan (tripˑ·t·fan),

n an essential amino acid used in the treatment of insomnia, depression, behavioral disorders, stress, and premenstrual syndrome (PMS). Also called
Enlarge picture
Chemical structure of tryptophan.


(Trp, W) (trip'tŏ-fan)
A nutritionally essential amino acid.


n one of the essential amino acids. See also amino acid.

tryptophan, tryptophane

Trp; a naturally occurring amino acid, existing in proteins. High levels of intake of d,l-tryptophan are thought to be a significant cause of atypical interstitial pneumonia in cattle. The actual toxic agent is 3-methylindole, a metabolic product of d,l-tryptophan in the rumen.

D, L-tryptophan
component of some roughages; high levels can cause acute bovine pulmonary emphysema and edema.
tryptophan oxygenase
first enzyme in the catabolic pathway for tryptophan. Essential step in the pathway to synthesis of nicotinamide nucleotides NAD+ and NADP+. Approximately 30% of the nicotinamide nucleotide requirement of some animals can be supplied through this enzyme. The cat is notably lacking in the latter capacity.
References in periodicals archive ?
A high-carbohydrate meal stimulates the release of insulin, which helps clear from the bloodstream those amino acids that compete with tryptophan, allowing more of the natural, sleep-inducing amino acids to enter the brain and manufacture sleep-inducing substances, such as serotonin and melatonin.
When the researchers doubled the amount of tryptophan in the mice's feed, the number of such cells rose by about 50 percent.
The monoamine which is most intensively studied in depression research is 5- hydroxytryptamine (5-HT; serotonin) a neurotransmitter synthesized from the essential amino acid tryptophan.
By contrast, recommendations for tryptophan supplements to aid in sleep are about 500 to 1,000 milligrams per dose.
A new determination method of tryptophan and its related compounds by high-performance liquid chromatography and its application to rumen fluid.
This study was designed to estimate genetic effects for protein, lysine and tryptophan percentages in maize under contrasting water regimes following the technique of generation mean analysis.
The present study evaluated the effects of externally applied tryptophan, fructan, or casein on manure fermentation, and noted the interactions among these additives and dietary Bs.
Once absorbed, tryptophan is used by the body to produce serotonin (a neurotransmitter) and melatonin (a hormone).
Tryptophan degradation is a known predictor of insomnia and is also related to inflammation, said co-authors Jack Losso and John Finley, professors in the School of Nutrition and Food Sciences at Louisiana State University Agricultural Center.