Xanthurenic acid is produced in: (A) Tyrosine metabolism, (B) Tryptophan metabolism, (C) Cysteine metabolism, (D) Valine metabolism
Answer is B. In the metabolism of Tryptophan, Kynurenin is an intermediate step. The accumulated Kynurenine is shunted to Xanthurenic acid. So, in pyridoxal deficiency, Xanthurenic acid is excreted in the urine.Ref: DM Vasudevan - Textbook of Biochemistry, 7th edition, page no: 240