<prompt> 1st product of tryptophan Catabolism -KynurenineXantheurenic acidBradykininMelatonin  <response>: Ans. is a i.e., Kynurenine Metabolism of tryptophano Tryptophan is an essential amino acidQ, containing indol ringQ. Tryptophan is oxidized to produce alanine which is glucogenic and acetyl-CoA which is ketogenic. Therefore, tryptophan is both glucogenic and ketogenic. Tryptophan is precursor for the biosynthess of niacinQ a vitaminQ, serotonin a neurotransmitter and melatoninQ a hormone.o Tryptophan metabolism occurs by two pathways: i kinurenine pathwayQ and ii serotonine pathway.1 Kynurenine pathway :- Tryptophan is oxidized to kynurenine, which is then converted to either niacin nicotinic acid or acetyl-CoA. In the reaction alanine is also produced. o Deficiency of tryptophan can cause deficiency of niacin if also deficient in diet. This can leads to Pallegra: dermatitis, diarrhea and dementia.o For every 60 mg of tryptophan, 1 mg. equivalent of niacin can be generatedQ.o In vitamin B6 deficiency the metabolism is shuted to xanthurenic acid. Therefore, xantheurenic acid excretion is increased in urine.2 Serotonin pathway:- Tryptophan is first oxidized to serotonine which is further converted to melatonin.o Serotonin secretion is increased in carcinoid syndrome which causes flushingQ. VasoconstrictionQ, diarrheaQ and bronchospasm respiratory distress. 