This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: vitamins, Subject name: Biochemistry
1st product of tryptophan catabolism is 
Select and explain. 
A. kynurenine, B. Bradykinin, C. PAF, D. Xantheurenate
A: kynurenine
Answer: A: kynurenine 
Explanation: Tryptophan is an aromatic essential amino acid The major metabolic fate of tryptophan is to be oxidized by tryptophan pyrrolase (tryptophan di-oxygenase) It is a hemoprotein. The enzyme is inducible by coicosteroids. <img src=" /> in tryptophan catabolism the first product is 3-hydroxykynurenine ref Satyanarayana 4th ed page 145