This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of protein and amino acid, Subject name: Biochemistry
[{'content': '1st product of tryptophan Catabolism \nSelect and explain. \nA. Kynurenine, B. Xantheurenic acid, C. Bradykinin, D. Melatonin', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Kynurenine is formed from tryptophan in presence of enzyme tryptophan pyrrolaseRef: DM Vasudevan - Textbook of Biochemistry, 7th edition, page no: 239, fig 18.8', 'role': 'assistant'}]