<prompt> The 1st product of tryptophan catabolism is?KynurenineBradykininPAFXanthurenate  <response>: 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 A T -formylkynurenine, catalyzed by kynurenine formylase, 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 