This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Structure and function of protein, Subject name: Biochemistry
Active sites of serine protease contain 
Select and explain. 
A. Histidine, B. Lysine or threonine, C. Arginine, D. Serine
D: Serine
Answer: D: Serine 
Explanation: Serine proteases name stems from the nucleophilic Ser (serine) in the enzyme active site Nucleophilicity of the catalytic Ser is typically dependent on a catalytic triad of Asp, His, and Ser residues, commonly referred to as the charge relay system Ref: biochemistry by U. Satyanarayana 3rd edition Pgno : 171