<prompt> First product of tryptophan catabolism is:KynerunineBradykininPAFXantheurenate  <response>: Ans. a KynerunineRef: Harpers Biochemistry, 30th ed. pg. 306-307 Tryptophan is degraded to amphibolic intermediates via the kynurenine-anthranilate pathway. Tryptophan oxygenase tryptophan pyrrolase opens the indole ring, incorporates molecular oxygen, and forms N-formyl kynurenine. Hydrolytic removal of the formyl group of N-formyl kynurenine, catalyzed by kynurenine fortnylase, produces kynurenine. Since kynureninase requires pyridoxal phosphate, excretion of xanthurenate in response to a tryptophan load is diagnostic of vitamin B6 deficiency. Hartnup disease reflects impaired intestinal and renal transport of tryptophan and other neutral amino acids. 