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
In transaminases, PLP is covalently attached to which amino acid? 
Select and explain. 
A. Glutamate, B. Lysine, C. Alanine, D. Threonine
B: Lysine
Answer: B: Lysine 
Explanation: Transaminases:- Transfer amino groups in reactions Coenzyme required is Vitamin B6 i.e. active form PLP (Pyridoxal phosphate) The PLP is linked with a e-amino group of a lysine residue, at the active site of the enzyme forming a Schiff base (imine linkage) ping pong bi bi mechanism is involved in transamination reaction. NOTE: Threonine does not undergo transamination. All the amino acids undergo transamination except: Proline Lysine Threonine Hydroxyproline