This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Which of the following vitamin acts as a cofactor for metabolism of sulphur containing amino acids? 
Select and explain. 
A. Folic acid, B. Biotin, C. Vit K, D. Pyridoxine
A: Folic acid
Answer: A: Folic acid 
Explanation: Methyl group in N5-methyl tetrahydrofolic acid (N5- methyl THFA) is used for synthesis of active methionine, which takes pa in transmethylation reactions. Such transmethylation reactions are required for synthesis of choline, epinephrine, creatine etc. Sulphur containing amino acids include cysteine and methionine. Ref: Textbook of Biochemistry by DM Vasudevan, 5th edition, Page 303.