First product of tryptophan catabolism is:

Ans. (a) KynerunineRef: Harper's 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.