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
The amino acid residue having an imino side chain is 
Select and explain. 
A. Lysine, B. Histidine, C. Tyrosine, D. Proline
D: Proline
Answer: D: Proline 
Explanation: Proline has pyrrolidine group in which imino group is there.Ref: DM Vasudevan - Textbook of Biochemistry, 7th edition, page no: 26