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|Systematic name||(S)-2-Amino-3-(1H-indol-3-yl)-propanoic acid|
|Molecular mass||204.23 g mol−1|
|Melting point||289 °C|
|Density||? g cm-3|
|Disclaimer and references|
Tryptophan (abbreviated as Trp or W) is one of the 20 standard amino acids, as well as an essential amino acid in the human diet. It is encoded in genetic code as the codon UGG. Only the L-stereoisomer of tryptophan is used in structural or enzyme proteins, but the D-stereoisomer is occasionally found in naturally produced peptides (for example, the marine venom peptide contryphan). The distinguishing structural characteristic of tryptophan is that it contains an indole functional group.
Biosynthesis and industrial production Edit
Plants and microorganisms commonly synthesize tryptophan from shikimic acid or anthranilate. The latter condenses with phosphoribosylpyrophosphate (PRPP), generating pyrophosphate as a by-product. After ring opening of the ribose moiety and following reductive decarboxylation, indole-3-glycerinephosphate is produced, which in turn is transformed into indole. In the last step, tryptophan synthase catalyzes the formation of tryptophan from indole and the amino acid, serine.
The industrial production of tryptophan is also biosynthetic and is based on the fermentation of serine and indole using either wild-type or genetically modified E. coli. The conversion is catalyzed by the enzyme tryptophan synthase.
For many organisms (including humans), tryptophan is an essential amino acid. This means that it cannot be synthesized by the organism and therefore must be part of its diet. The principal function of amino acids including tryptophan are as building blocks in protein biosynthesis. In addition, tryptophan functions as a biochemical precursor for the following compounds (see also figure to the right):
- Serotonin (a neurotransmitter), synthesized via tryptophan hydroxylase. Serotonin, in turn, can be converted to melatonin (a neurohormone), via N-acetyltransferase and 5-hydroxyindole-O-methyltransferase activities.
- Niacin is synthesized from tryptophan via kynurenine and quinolinic acids as key biosynthetic intermediates.
In bacteria that synthesize tryptophan, high cellular levels of this amino acid activate a repressor protein, which binds to the trp operon. [How to reference and link to summary or text] Binding of this repressor to the tryptophan operon prevents transcription of downstream DNA that codes for the enzymes involved in the biosynthesis of tryptophan. So high levels of tryptophan prevent tryptophan synthesis through a negative feedback loop and, when the cell's tryptophan levels are reduced, transcription from the trp operon resumes. The genetic organization of the trp operon thus permits tightly regulated and rapid responses to changes in the cell's internal and external tryptophan levels.
Tryptophan is a routine constituent of most protein-based foods or dietary proteins. It is particularly plentiful in chocolate, oats, bananas, mangoes, dried dates, milk, yogurt, cottage cheese, red meat, eggs, fish, poultry, sesame, chickpeas, sunflower seeds, pumpkin seeds, spirulina, and peanuts. It is also found in turkey at a level typical of poultry in general.
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Use as a dietary supplementEdit
For some time, tryptophan was available in health food stores as a dietary supplement, although it is common in dietary protein. Many people found tryptophan to be a safe and reasonably effective sleep aid, probably due to its ability to increase brain levels of serotonin (a calming neurotransmitter when present in moderate levels) and/or melatonin (a sleep-inducing hormone secreted by the pineal gland in response to darkness or low light levels).
Clinical research tends to confirm tryptophan's effectiveness as a sleep aid and for a growing variety of other conditions typically associated with low serotonin levels or activity in the brain such as premenstrual dysphoric disorder  and seasonal affective disorder. In particular, tryptophan has been showing considerable promise as an antidepressant alone, and as an "augmenter" of antidepressant drugs. However others have questioned the reliability of these clinical trials.
5-HTP readily crosses the blood-brain barrier and in addition is rapidly decarboxylated to serotonin (5-hydroxytryptamine or 5-HT) and therefore may be useful for the treatment of depression. However serotonin has a relatively short half-life since it is rapidly metabolized by monoamine oxidase, and therefore is likely to have limited efficacy. It is marketed in Europe for depression and other indications under the brand names Cincofarm and Tript-OH.
In the United States, 5-HTP does not require a prescription, as it is covered under the Dietary Supplement Act. However, since the quality of dietary supplements is not regulated by the FDA, the quality of dietary and nutritional supplements tends to vary, and there is no guarantee that the label accurately depicts what the bottle contains.
Tryptophan supplements and EMS Edit
Although currently available for purchase, in 1989 a large outbreak (1500 cases of permanent disability including at least 37 deaths) of a disabling autoimmune illness called eosinophilia-myalgia syndrome (EMS) was traced by some epidemiological studies to L-tryptophan supplied by a Japanese manufacturer, Showa Denko KK. It was further hypothesized that one or more trace impurities produced during the manufacture of tryptophan may have been responsible for the EMS outbreak. However, many people who consumed Showa Denko L-tryptophan did not develop EMS and cases of EMS have occurred prior to and after the 1989 epidemic. Furthermore the methodology used in the initial epidemiological studies has been criticized. An alternative explanation for the 1989 EMS outbreak is that large doses of tryptophan produce metabolites which inhibit the normal degradation of histamine and excess histamine in turn has been proposed to cause EMS.
Most tryptophan was banned from sale in the US in 1991, and other countries followed suit. Tryptophan from one manufacturer, of six, continued to be sold for manufacture of baby formulas. A Rutgers Law Journal article observed, "Political pressures have played a role in the FDA's decision to ban L-tryptophan as well as its desire to increase its regulatory power over dietary supplements."
At the time of the ban, the FDA did not know, or did not indicate, that EMS was caused by a contaminated batch, and yet, even when the contamination was discovered and the purification process fixed, the FDA maintained that L-tryptophan was unsafe. In February 2001, the FDA loosened the restrictions on marketing (though not on importation), but still expressed the following concern:
- "Based on the scientific evidence that is available at the present time, we cannot determine with certainty that the occurrence of EMS in susceptible persons consuming L-tryptophan supplements derives from the content of L-tryptophan, an impurity contained in the L-tryptophan, or a combination of the two in association with other, as yet unknown, external factors."
Since 2002, L-tryptophan has been sold in the U.S. in its original form. Several high-quality sources of L-tryptophan do exist, and are sold in many of the largest health food stores nationwide. Indeed, tryptophan has continued to be used in clinical and experimental studies employing human patients and subjects.
In recent years in the U.S., compounding pharmacies and some mail-order supplement retailers have begun selling tryptophan to the general public. Tryptophan has also remained on the market as a prescription drug (Tryptan), which some psychiatrists continue to prescribe, particularly as an augmenting agent for people who are unresponsive to antidepressant drugs.[How to reference and link to summary or text]
Turkey meat and drowsinessEdit
One widely-held belief is that heavy consumption of turkey meat (as for example in a Thanksgiving feast) results in drowsiness, which has been attributed to high levels of tryptophan contained in turkey. While turkey does contain high levels of tryptophan, the amount is comparable to that contained in most other meats. Furthermore, postprandial Thanksgiving sedation may have more to do with what is consumed along with the turkey, in particular carbohydrates, rather than the turkey itself.
It has been demonstrated in both animal models and in humans that ingestion of a meal rich in carbohydrates triggers release of insulin. Insulin in turn stimulates the uptake of large neutral branched-chain amino acids (LNAA) but not tryptophan (trp) into muscle, increasing the ratio of trp to LNAA in the blood stream. The resulting increased ratio of tryptophan to large neutral amino acids in the blood reduces competition with other amino acids for the large neutral amino acid transporter protein for uptake of tryptophan across the blood-brain barrier into the central nervous system (CNS). Once inside the CNS, tryptophan is converted into serotonin in the raphe nuclei by the normal enzymatic pathway. The resultant serotonin is further metabolised into melatonin by the pineal gland. Hence, these data suggest that "feast-induced drowsiness," and in particular, the common American post-Thanksgiving dinner drowsiness, may be the result of a heavy meal rich in carbohydrates which, via an indirect mechanism, increases the production of sleep-promoting serotonin and melatonin in the brain.
- ↑ IUPAC-IUBMB Joint Commission on Biochemical Nomenclature. Nomenclature and Symbolism for Amino Acids and Peptides. Recommendations on Organic & Biochemical Nomenclature, Symbols & Terminology etc. URL accessed on 2007-05-17.
- ↑ Pallaghy PK, Melnikova AP, Jimenez EC, Olivera BM, Norton RS (1999). Solution structure of contryphan-R, a naturally-occurring disulfide-bridged octapeptide containing D-tryptophan: comparison with protein loops. Biochemistry 38 (35): 11553-9.
- ↑ Hopkins FG, Cole SW (1901). A contribution to the chemistry of proteids: Part I. A preliminary study of a hitherto undescribed product of tryptic digestion. J. Physiol. (Lond.) 27 (4-5): 418-28.
- ↑ Cox GJ, King H (1943). L-Tryptophane. Organic Syntheses Collected Volume 2: 612-616.
- ↑ Radwanski ER, Last RL (1995). Tryptophan biosynthesis and metabolism: biochemical and molecular genetics. Plant Cell 7 (7): 921-34.
- ↑ Ikeda M (2002). Amino acid production processes. Adv. Biochem. Eng. Biotechnol. 79: 1-35.
- ↑ Fernstrom JD (1983). Role of precursor availability in control of monoamine biosynthesis in brain. Physiol. Rev. 63 (2): 484-546.
- ↑ Schaechter JD, Wurtman RJ (1990). Serotonin release varies with brain tryptophan levels. Brain Res. 532 (1-2): 203-10.
- ↑ 9.0 9.1 Wurtman RJ, Anton-Tay F (1969). The mammalian pineal as a neuroendocrine transducer. Recent Prog. Horm. Res. 25: 493-522.
- ↑ Ikeda M, Tsuji H, Nakamura S, Ichiyama A, Nishizuka Y, Hayaishi O (1965). Studies on the biosynthesis of nicotinamide adenine dinucleotide. II. A role of picolinic carboxylase in the biosynthesis of nicotinamide adenine dinucleotide from tryptophan in mammals. J. Biol. Chem. 240: 1395-401.
- ↑ Ledochowski M, Widner B, Murr C, Sperner-Unterweger B, Fuchs D (2001). Fructose malabsorption is associated with decreased plasma tryptophan. Scand. J. Gastroenterol. 36 (4): 367-71.
- ↑ Ledochowski M, Sperner-Unterweger B, Widner B, Fuchs D (1998). Fructose malabsorption is associated with early signs of mental depression. Eur. J. Med. Res. 3 (6): 295-8.
- ↑ Tryptophan background
- ↑ 14.0 14.1 14.2 Joanne Holden, Nutrient Data Laboratory, Agricultural Research Service. USDA National Nutrient Database for Standard Reference, Release 20. United States Department of Agriculture. URL accessed on 2007-10-02.
- ↑ Rambali B, Andel I van, Schenk E, Wolterink G, Werken G van de, Stevenson H, Vleeming W (2002). [The contribution of cocoa additive to cigarette smoking addiction]. RIVM (report 650270002/2002).- The National Institute for Public Health and the Environment (Netherlands)
- ↑ Wurtman RJ, Hefti F, Melamed E (1980). Precursor control of neurotransmitter synthesis. Pharmacol. Rev. 32 (4): 315-35.
- ↑ Wurtman RJ, Larin F, Axelrod J, Shein HM, Rosasco K (1968). Formation of melatonin and 5-hydroxyindole acetic acid from 14C-tryptophan by rat pineal glands in organ culture. Nature 217 (5132): 953-4.
- ↑ Ruddick JP, Evans AK, Nutt DJ, Lightman SL, Rook GA, Lowry CA (2006). Tryptophan metabolism in the central nervous system: medical implications. Expert reviews in molecular medicine 8 (20): 1-27.
- ↑ Hartmann E (1982). Effects of L-tryptophan on sleepiness and on sleep. Journal of psychiatric research 17 (2): 107-13.
- ↑ Schneider-Helmert D, Spinweber CL (1986). Evaluation of L-tryptophan for treatment of insomnia: a review. Psychopharmacology (Berl.) 89 (1): 1-7.
- ↑ Wyatt RJ, Engelman K, Kupfer DJ, Fram DH, Sjoerdsma A, Snyder F. (1970 Oct 24). Effects of L-tryptophan (a natural sedative) on human sleep.. Lancet 1970 Oct 24,2 (7678): 842-6.
- ↑ research summary of Dr. Richard Wurtman, MIT. URL accessed on 2007-08-12.
- ↑ Steinberg S, Annable L, Young SN, Liyanage N (1999). A placebo-controlled clinical trial of L-tryptophan in premenstrual dysphoria. Biol. Psychiatry 45 (3): 313-20.
- ↑ Lam RW, Levitan RD, Tam EM, Yatham LN, Lamoureux S, Zis AP (1997). L-tryptophan augmentation of light therapy in patients with seasonal affective disorder. Canadian journal of psychiatry. Revue canadienne de psychiatrie 42 (3): 303-6.
- ↑ Jepson TL, Ernst ME, Kelly MW (1999). Current perspectives on the management of seasonal affective disorder. J Am Pharm Assoc (Wash) 39 (6): 822-9.
- ↑ 26.0 26.1 Thomson J, Rankin H, Ashcroft GW, Yates CM, McQueen JK, Cummings SW (1982). The treatment of depression in general practice: a comparison of L-tryptophan, amitriptyline, and a combination of L-tryptophan and amitriptyline with placebo. Psychological medicine 12 (4): 741-51.
- ↑ Levitan RD, Shen JH, Jindal R, Driver HS, Kennedy SH, Shapiro CM (2000). Preliminary randomized double-blind placebo-controlled trial of tryptophan combined with fluoxetine to treat major depressive disorder: antidepressant and hypnotic effects. Journal of psychiatry & neuroscience : JPN 25 (4): 337-46.
- ↑ Meyers S (2000). Use of neurotransmitter precursors for treatment of depression. Alternative medicine review : a journal of clinical therapeutic 5 (1): 64-71.
- ↑ Shaw K, Turner J, Del Mar C (2002). Tryptophan and 5-hydroxytryptophan for depression. Cochrane database of systematic reviews (Online) (1): CD003198.
- ↑ Kostowski W, Bidzinski A, Hauptmann M, Malinowski JE, Jerlicz M, Dymecki J (1978). Brain serotonin and epileptic seizures in mice: a pharmacological and biochemical study. Pol J Pharmacol Pharm 30 (1): 41-7.
- ↑ Turner EH, Loftis JM, Blackwell AD (2006). Serotonin a la carte: supplementation with the serotonin precursor 5-hydroxytryptophan. Pharmacol Ther 109 (3): 325-38.
- ↑ Hardebo JE, Owman C (1980). Barrier mechanisms for neurotransmitter monoamines and their precursors at the blood-brain interface. Ann NeurolAnn Neurol 8 (1): 1-31.
- ↑ Slutsker L, Hoesly FC, Miller L, Williams LP, Watson JC, Fleming DW (1990). Eosinophilia-myalgia syndrome associated with exposure to tryptophan from a single manufacturer. JAMA 264 (2): 213-7.
- ↑ Back EE, Henning KJ, Kallenbach LR, Brix KA, Gunn RA, Melius JM (1993). Risk factors for developing eosinophilia myalgia syndrome among L-tryptophan users in New York. J. Rheumatol. 20 (4): 666-72.
- ↑ Kilbourne EM, Philen RM, Kamb ML, Falk H (1996). Tryptophan produced by Showa Denko and epidemic eosinophilia-myalgia syndrome. The Journal of rheumatology. Supplement 46: 81-8; discussion 89-91.
- ↑ 36.0 36.1 FDA Information Paper on L-tryptophan and 5-hydroxy-L-tryptophan
- ↑ Mayeno AN, Lin F, Foote CS, Loegering DA, Ames MM, Hedberg CW, Gleich GJ (1990). Characterization of "peak E," a novel amino acid associated with eosinophilia-myalgia syndrome. Science 250 (4988): 1707-8.
- ↑ Ito J, Hosaki Y, Torigoe Y, Sakimoto K (1992). Identification of substances formed by decomposition of peak E substance in tryptophan. Food Chem. Toxicol. 30 (1): 71-81.
- ↑ Shapiro S (1996). Epidemiologic studies of the association of L-tryptophan with the eosinophilia-myalgia syndrome: a critique. The Journal of rheumatology. Supplement 46: 44-58; discussion 58-9.
- ↑ Horwitz RI, Daniels SR (1996). Bias or biology: evaluating the epidemiologic studies of L-tryptophan and the eosinophilia-myalgia syndrome. The Journal of rheumatology. Supplement 46: 60-72.
- ↑ Smith MJ, Garrett RH (2005). A heretofore undisclosed crux of eosinophilia-myalgia syndrome: compromised histamine degradation. Inflamm. Res. 54 (11): 435-50.
- ↑ Beisler JH (2000). Dietary Supplements and Their Discontents: FDA Regulation and the Dietary Supplement Health and Education Act of 1994 (L-tryptophan Section). Rutgers Law Journal.
- ↑ FDA Tryptophan Recall
- ↑ Raphals P (2000). Does medical mystery threaten biotech?. Science 250: 4981.
- ↑ About.com: Does Eating Turkey Make You Sleepy?. URL accessed on 2007-08-17.
- ↑ Howstuffworks.com: Is there something in turkey that makes you sleepy?. URL accessed on 2007-08-17.
- ↑ Chemistry.org: Thanksgiving, Turkey, and Tryptophan. URL accessed on 2007-08-17.
- ↑ 48.0 48.1 48.2 Fernstrom JD, Wurtman RJ (1971). Brain serotonin content: increase following ingestion of carbohydrate diet. Science 174 (13): 1023-5.
- ↑ 49.0 49.1 Lyons PM, Truswell AS (1988). Serotonin precursor influenced by type of carbohydrate meal in healthy adults. Am. J. Clin. Nutr. 47 (3): 433-9.
- ↑ 50.0 50.1 50.2 Wurtman RJ, Wurtman JJ, Regan MM, McDermott JM, Tsay RH, Breu JJ (2003). Effects of normal meals rich in carbohydrates or proteins on plasma tryptophan and tyrosine ratios. Am. J. Clin. Nutr. 77 (1): 128-32.
- ↑ 51.0 51.1 Afaghi A, O'Connor H, Chow CM (2007). High-glycemic-index carbohydrate meals shorten sleep onset. Am. J. Clin. Nutr. 85 (2): 426-30.
- ↑ Pardridge WM, Oldendorf WH (1975). Kinetic analysis of blood-brain barrier transport of amino acids. Biochim. Biophys. Acta 401 (1): 128-36.
- ↑ Maher TJ, Glaeser BS, Wurtman RJ (1984). Diurnal variations in plasma concentrations of basic and neutral amino acids and in red cell concentrations of aspartate and glutamate: effects of dietary protein intake. Am. J. Clin. Nutr. 39 (5): 722-9.
See also Edit
- Tryptophan metabolism
- Tryptophan catabolism (early stages)
- Tryptophan catabolism (later stages)
- Computational Chemistry Wiki
- Thanksgiving, Turkey, and Tryptophan
- FDA Information Paper on L-tryptophan and 5-hydroxy-L-tryptophan
- Snopes article debunking the turkey–drowsiness connection
- The FDA Ban of L-Tryptophan: Politics, Profits and Prozac
- Effects of Tryptophan Depletion on the Performance of an Iterated Prisoner's Dilemma Game in Healthy Adults - Nature Neuropsychopharmacology
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