This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Proteins and Amino Acids, Subject name: Biochemistry
[{'content': 'First product of tryptophan catabolism is: \nSelect and explain. \nA. Kynerunine, B. Bradykinin, C. PAF, D. Xantheurenate', 'role': 'user'}, {'content': "Answer: A \nExplanation: 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.", 'role': 'assistant'}]