This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Biochemistry
Epinephrine is synthesized from norepinephrine by 
Select and explain. 
A. Hydroxylation, B. N-methylation, C. Deamination, D. Carboxylation
B: N-methylation
Answer: B: N-methylation 
Explanation: Norepinephrine can be conveed into epinephrine by the enzyme phenylethanolamine N-methyltransferase with S-adenosyl-L-methionine as cofactor.