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
All of the following vitamins are involved in sulphur containing amino acid metabolism except? 
Select and explain. 
A. Vitamin B3, B. Vitamin B6, C. Vitamin B9, D. Vitamin B12
A: Vitamin B3
Answer: A: Vitamin B3 
Explanation: 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