This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Urea cycle, Subject name: Biochemistry
All of the following are transaminated EXCEPT: 
Select and explain. 
A. d- amino group of ornithine, B. a- amino group of proline, C. a- amino group of serine, D. a- amino group of cysteine
B: a- amino group of proline
Answer: B: a- amino group of proline 
Explanation: Only a amino group takes pa in transamination. Except:- d -amino group (non-a) of ornithine takes pa in transamination, where enzyme is OAT (Ornithine Amino Transferase). Out of the 20 amino acids, 3 amino acids do not take pa in transamination. Proline Lysine Threonine