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': 'All of the following vitamins are involved in sulphur containing amino acid metabolism except? \nSelect and explain. \nA. Vitamin B3, B. Vitamin B6, C. Vitamin B9, D. Vitamin B12', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Vitamin B6, B9 and B12 are involved in sulphur containing amino acid metabolism. Vitamin B6 (Pyridoxine) is the co-enzyme of cystathionine b synthase. Vitamin B9 (Folic acid) and B12 (Cobalamin) are involved in the conversion of homocysteine to methionine by methionine synthase. Clinical impoance: Reference: Harpers illustrated biochemistry 30th edition', 'role': 'assistant'}]