Tryptophan Definition - What Is Tryptophan ? - Health Article

Tryptophan Definition - What Is Tryptophan ?

What is Tryptophan?

Tryptophan is one of the more than twenty in man-occurring amino acids that are used for protein synthesis, and belongs to the category of essential amino acids. This means that it can not be synthesized by the human organism and must therefore be consumed in the diet. The body is thus entirely dependent on its supply via the power supply.

Tryptophan is a precursor in the biosynthesis of many indole derivatives such as the neurotransmitter serotonin and kynurenine. Serotonin affects mood, self-confidence, sleep, emotion, sexual activity and appetite. In addition, tryptophan in the body used as a raw material for protein synthesis.


Frederick Gowland Hopkins and Sydney Cole discovered tryptophan in 1901 after having been isolated from casein protein. Its molecular structure some time later clarified by Ellinger and Flamand. The first synthesis of tryptophan was in 1949, but in the 80s of the last century, the chemical synthesis of tryptophan was replaced by fermentation procedures which gave greatly increased yields.

The discovery that tryptophan is an indispensable nutritional ingredient is took place in the 50s of the last century. In the 70s and 80s of the last century it was discovered that tryptophan acts sleep-promoting. In this period, tryptophan was used as a therapeutic agent to combat chronic insomnia.

In the 80s of the last century came the first tryptophan-containing dietary supplements on the market. Shortly thereafter, in 1988 and 1989, there was an outbreak of eosinophilia-myalgia syndrome (EMS) among users of tryptophan supplement, with 37 deceased persons and more than 1,500 users of tryptophan were seriously ill. After investigation, the source of the outbreak traced to a single raw material manufacturer, the "Showa Denko Company of Japan," and the cause appeared to lie in a new way of tryptophan synthesis genetically engineered bacteria. As a result, the raw material tryptophan was contaminated with a foreign substance. As a result of the EMS outbreak forbade the US Food and Drug Administration (FDA) all over-the-counter sales of tryptophan supplements, which was only allowed limited use of tryptophan produced by producers in the United States. In several other countries, L-tryptophan has been banned. Since 1989 there are no more incidents reported after the use of tryptophan supplements. In the US, the ban was lifted in 2001.


Tryptophan is a non-polar hydrophobic amino acid. D amino acid side chain of tryptophan is lipophilic and aromatic. Therefore, it is poorly soluble in water. Its isoelectric point is 5.89, the pKCOOH is 2.4, the pKNH2 9.3 (both at 25 ° C).

Free tryptophan and protein-bound tryptophan units fluoresce in ultra violet radiation. Upon excitation with ultraviolet light having a wavelength of 280 nm, followed by a fluorescence emission between 308-350 nm, which is dependent on the polarity of the direct vicinity of tryptophan. If there are present in proteins tryptophan units, the fluorescence of tryptophan surpasses the fluorescence of the other aromatic amino acids (tyrosine and phenylalanine).

Biosynthesis and industrial production
In many organisms, including humans, is an essential amino acid tryptophan. This means that it is essential to human life, can not be synthesized by the organism and must therefore be consumed in the diet. Plants and micro-organisms can indeed produce L-tryptophan.

Plants and microorganisms are able to produce L-tryptophan, inter alia from shikimic acid or anthranilic acid. The latter reacts with fosforibosylpyrofosfaat with elimination of diphosphate. After ring opening of the ribose-unit, followed by decarboxylation and dehydration is eventually indole-3-glycerol phosphate is obtained, which is converted to indole. In the last step, tryptophan synthase catalyzes the conversion of this latter compound in glyceraldehyde-3-phosphate with the indole intermediate substance bound to the enzyme and with the intervention of serine.

Industrial synthesis
The industrial production of L-tryptophan is based on the fermentation of L-serine and indole and uses a (wild-type or genetically modified) mutant strains as B. amyloliquefaciens, B. subtilis, C. glutamicum or E. coli. The reaction is catalyzed by the enzyme tryptophan synthase.

Occurrence in food

People keep a relatively low body stores of tryptophan in the body is the lowest of all amino acids. However, only relatively small amounts in order to meet the need. The recommended daily intake is between 250 mg and 425 mg per day (3.5 to 6.0 mg per kg of body weight per day).

Tryptophan occurs in most protein-rich food, although it all amino acids that occurs least frequently used for protein synthesis. The typical daily intake for many adults is about 900 to 1000 mg. Some common food sources of tryptophan are oats, bananas, prunes, milk, tuna, cheese, bread, poultry (chicken, turkey, pheasant, quail), peanuts and chocolate. Also, some seeds such as pumpkin seeds, sesame seeds, sunflower seeds, almonds and lentils are relatively rich in tryptophan.

 Tryptophan is one of the more than twenty in man Tryptophan Definition - What Is Tryptophan ?

A glass of warm milk before bedtime is an ancient remedy for insomnia. However, it has never been scientifically proven that the tryptophan in the milk that creates this effect. The sleepy feeling that people experience these food-traditional turkey on Thanksgiving in the United States-has been attributed to tryptophan.

As a dietary supplement
L-Tryptophan (the variant that occurs in nature) is also available as a supplement in some drugstores, pharmacies and even smart shops. It can sleep-promoting, anxiety and absorbing work as an antidepressant. Also, it has a positive influence on the development of the muscles, for example, body builders. L-Tryptophan works closely with vitamin B6 pyridoxine ie. In most of the added tryptophan supplements is vitamin B6.

Some medications, particularly antidepressants that increase the availability of serotonin (such as SSRIs and MAOIs) should not be taken simultaneously with L-tryptophan.

It can also have side effects (adverse events). Blurred vision, dizziness, fatigue and light are mentally unwell - one feels very strange and hazy - can occur.


Diabetic ketoacidosis appears to deplete the plasma tryptophan levels. Tryptophan deficiency causes cataract in rats. A deficiency of the amino acid stops the chromatin degradation in the secondary lens fibers of rats.


The amino acid tryptophan is the precursor of several important products, such as serotonin, melatonin, vitamin B3, indoleacetic acid, insect eye and pigments in a number of alkaloids.

Tryptophan supplementation may play a potential role in repairing age-related circadian changes.
  • Protein Synthesis - The principal role of tryptophan in the human body is as a component of proteins. Because of all the amino acids tryptophan in relatively low concentrations present in the diet, it is relatively less available and it is assumed that tryptophan plays a rate-limiting role during protein synthesis. As with all other amino acids, the L-isomer exclusively used in the protein synthesis. Only the L-isomer can also cross the blood-brain barrier.
  • Kynurenine synthesis - After protein synthesis, is the second most common metabolic pathway of tryptophan synthesis of kynurenine. Upon decomposition of tryptophan, approximately 90% of the degraded tryptophan converted to kynurenine. Kynurenine is the precursor of kynurenine acid and quinolinic acid, which may affect neurotransmitter metabolism. Kynurenine acid is a glutamate receptor antagonist, and quinolinic acid is an NMDA receptor agonist. Kynurenine is also involved in an ultraviolet (UV) filter that the retina of the eye protects against UV-rays. The effectiveness of such protection decreases with age, which contributes to the normal age-related changes in staining and fluorescence of the eye lens, which has an influence on the visual function and in some individuals can play a role in the formation of cataracts.
  • Synthesis of serotonin - Tryptophan is the sole precursor of serotonin. Although only 3% of the tryptophan is used for serotonin synthesis by the body, serotonin synthesis is one of the major metabolic pathways of tryptophan and a subject of intensive research. It is estimated that only 1% of the tryptophan is used for serotonin synthesis in the brains. It is estimated that 95% of serotonin is found in mammals in the gastro-intestinal tract. But in spite of the relatively low concentration of serotonin in the brains compared with those in the rest of the body, it has great impact serotonin as a neurotransmitter and neuromodulator and is involved in numerous psychiatric disorders and psychological processes.
  • Synthesis of melatonin - Melatonin is a hormone that is produced from serotonin in the tryptophan / serotonin metabolism route. It regulates circadian rhythms and affects the reproductive and immune systems, as well as digestive processes and the motility of the stomach.
  • Tryptamine synthesis - In addition, a tryptamine of tryptophan-derived biologically active compound. The direct decarboxylation of tryptophan leads to the synthesis of small quantities of tryptamine (i.e., in the concentration range of ng / g), which is an important neuromodulator of serotonin. Studies with animals have shown that tryptamine acts as a regulator for the balance between excitatory and inhibitory functions of serotonin, and in other cases, acts as a neurotransmitter tryptamine with specific receptors, independently of serotonin.
  • Synthesis of NAD / NADP - Tryptophan plays a role as a substrate for the synthesis of coenzymes NAD (nicotinamide adenine dinucleotide) and NAD phosphate (NADP). NAD and NADP are co-enzymes that are essential for electron transfer reactions (ie, redox reactions) in all living cells. These co-enzymes are synthesized from tryptophan consumed through the kynurenine pathway metabolism or from niacin (vitamin B3).
  • Synthesis of vitamin B3 - Tryptophan can act as a substrate for the synthesis of nicotinic acid (vitamin B3) in the liver via the above-mentioned kynurenine / quinolinic acid route. There are, however, needed nine transposition steps, and this conversion occurs little efficient. There is about 60 mg tryptophan, in order to make a few milligrams of nicotinic acid. The recommended daily allowance of niacin is 17 mg per day. The intake of vitamin B3 from the diet is usually so high that there is little need for additional synthesis from tryptophan.
  • Other Features - Tryptophan also affects other neurotransmitters in the central nervous system and joints. The concentrations of dopamine, noradrenaline and beta-endorphin are increasing after oral ingestion of tryptophan. Through the serotonin synthesis tryptophan probably also plays a role in modulation of the endocrine system (cortisol, prolactin and growth hormone).

After consuming dietary tryptophan from dietary protein is released and easily absorbed through the capillaries in the intestinal wall. It is transported to the liver via the portal vein.

The absorption and the use of tryptophan are vulnerable to both primary congenital genetic abnormalities and secondary intestinal disorders. In addition, there are several genetic autoimmune diseases of the bowel that affect the absorption, such as celiac disease and Crohn's disease. These disorders are usually diagnosed until adulthood.

When Hartnup disease, there has been decreased reabsorption of tryptophan in the kidneys as well as an impaired uptake (malabsorption) of tryptophan in the intestine. Its neurological symptoms are partly caused by degradation products of tryptophan in the intestine. This also plays a role in the blue diaper syndrome. Bacterial degradation of tryptophan in the gut then leads to excessive production of indoles. These indoles are converted in the liver in indicaan, which is water soluble, and then is excreted in the urine. When exposed to the air oxidizes this compound, which produces a peculiar indigo blue discoloration of the urine. Symptoms typically include gastrointestinal disturbances, fever and visual problems.


Once tryptophan consumed is divided on the human body in the circulatory system. In contrast to the other 19 amino acids used for protein synthesis, it is estimated that 75% to 85% of the tryptophan bound to circulating albumin (some estimates go even up to 95%). It is mainly the unbound, free tryptophan that is available for transport across the blood-brain barrier (BBB). As tryptophan has a higher affinity for the transport protein that can transport across the blood-brain barrier (BBB transport protein) than for albumin, will (bound to albumin) tryptophan which is located in the vicinity of the blood-brain barrier, likely to dissociate from the albumin in order to be included in the brains. Because of this difference in affinity, some researchers have concluded that up to 75% of the albumin-bound tryptophan is available for transport across the blood-brain barrier. In the bloodstream tryptophan competes with other large neutral amino acids (such as histidine, isoleucine, leucine, methionine, phenylalanine, threonine, tyrosine, and valine) for the BHB-transport protein. Since the BHB-transport protein is almost saturated at normal plasma concentrations of amino acids, it is very susceptible to competitive inhibition. Because of the competition between the large neutral amino acids to the transport protein, the bioavailability of tryptophan across the blood-brain barrier is best expressed by the ratio of tryptophan to the sum of competing amino acids. Therefore, a change of this ratio has a significant effect on the concentrations of tryptophan that is available in the brains for serotonin synthesis. Taking a cocktail of large neutral amino acids without tryptophan, is the fastest way to produce a tryptofaantekort and is regularly used in scientific research for that purpose.

Also other influences, such as stress, insulin resistance, a deficiency of magnesium or vitamin B6 as well as increasing age, have an influence on the rate of serotonin synthesis. Nevertheless affect its fluctuations in the ratio between tryptophan and competing amino acids, as well as changing the availability of tryptophan in the diet, the two factors that are most strongly this process.

To a certain extent the availability of tryptophan for the brains can be increased by intake of carbohydrates, and are reduced by the intake of proteins. Carbohydrate intake has no influence on the levels of tryptophan in the blood stream, but it can reduce the concentrations of competing amino acids by activation of insulin, which is the relative availability of tryptophan for transport increases towards the brains. Protein contains precisely relatively low concentrations of tryptophan and the ingestion of a meal protein increases the concentration of competing amino acids relative to tryptophan. The result is a greater competitive advantage of competing amino acids with respect to transport of tryptophan across the blood-brain barrier. Through the consumption of carbohydrates or proteins, the availability of tryptophan for the synthesis of serotonin can be changed. Only small amounts of protein (from about 4%) in a carbohydrate meal can avoid increasing the competitive advantage of tryptophan. However, it is unlikely that the changes in the relative availability of tryptophan via manipulation of the protein or carbohydrate intake, are substantial enough to have a significant impact on the behavior of a healthy individual.

In addition to these dietary factors which affect the availability of tryptophan for the synthesis of serotonin, has also been demonstrated that the use of alcohol decreases the ratio between tryptophan and competing amino acids. The decrease is about 10% after about 30 minutes, and 20% -25% about half to two hours after ingestion. This suggests that the serotonin synthesis is reduced under these conditions. Where an average person this level of serotonin depletion can probably tolerate without affecting the behavior in vulnerable individuals may experience a greater negative effect (eg 50% or more). This vulnerability is possible due to a pre-existing impaired serotonin function, which could be further affected by the reduced serotonin synthesis after consumption of alcohol.

A possible excess of tryptophan is converted to xanthureen acid, which can then be excreted by the kidneys.

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