This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
[{'content': 'The 1st product of tryptophan catabolism is? \nSelect and explain. \nA. Kynurenine, B. Bradykinin, C. PAF, D. Xanthurenate', 'role': 'user'}, {'content': 'Answer: A \nExplanation: 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.\nHydrolytic 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.\nHartnup disease reflects impaired intestinal and renal transport of tryptophan and other neutral amino acids', 'role': 'assistant'}]