This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Proteins and Amino Acids, Subject name: Biochemistry
Maximum buffering capacity at physiological pH is for: 
Select and explain. 
A. Valine, B. Cysteine, C. Histidine, D. Glycine
C: Histidine
Answer: C: Histidine 
Explanation: Ans: c (Histidine) Ref: Vasudevan, 4th ed, p. 195; 5th ed, p. 211Pka value of histidine is 6.8; hence its responsible for maximum buffering at physiological pH.HISTIDINE Semi essential amino acid. Basic amino acid (So positively charged at physiological pH) Forms FIGLU as an intermediary step during formation of formimino THFA (one carbon pool).F1GLU is excreted in urine when folic acid is deficient.