This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Classification and metabolism of amino acids, Subject name: Biochemistry
Xanthurenic acid is the metabolite in the metabolism of 
Select and explain. 
A. Uric acid, B. Xanthine, C. Tryptophan, D. Uronic acid
C: Tryptophan
Answer: C: Tryptophan 
Explanation: 3-Hydroxy Kynurenine is one of the intermediate in tryptophan catabolism, which gets conveed to next intermediate and this conversion requires vitamin B6/ PLP. So, in B6 deficiency, this reaction does not occur and 3-Hydroxy Kynurenine is diveed to form alternate metabolite, Xanthurenic acid (See fig), which is excreted in urine