Constit. of many plants. Enzymatic hydrol. prod. of most plant and animal proteins. Dietary supplement, nutrient Tryptophan is one of the 20 standard amino acids, as well as an essential amino acid in the human diet. 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). (Wikipedia)


Tryptophan is an essential amino acid which is the precursor of serotonin. Serotonin is a brain neurotransmitter, platelet clotting factor and neurohormone found in organs throughout the body. Metabolism of tryptophan to serotonin requires nutrients such as vitamin B6, niacin and glutathione. Niacin is an important metabolite of tryptophan. High corn or other tryptophan-deficient diets can cause pellagra, which is a niacin-tryptophan deficiency disease with symptoms of dermatitis, diarrhea and dementia. Inborn errors of tryptophan metabolism exist where a tumor (carcinoid) makes excess serotonin. Hartnup's disease is a disease where tryptophan and other amino acids are not absorbed properly. Tryptophan supplements may be useful in each condition, in carcinoid replacing the over-metabolized nutrient and in Hartnup's supplementing a malabsorbed nutrient. Some disorders of excess tryptophan in the blood may contribute to mental retardation. 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 fragments 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. Adults' minimum daily requirement is 3 mg/kg/day or about 200 mg a day. This may be an underestimation, for there are 400 mg of tryptophan in just 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 per pound.

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