This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Structure & Function of Protein, Subject name: Biochemistry
In determining protein structure, mercaptoethanol is used to: 
Select and explain. 
A. Identify C-terminal residue, B. Denature protein, C. Reduce disulfide bonds, D. Oxidize disulfide bonds
C: Reduce disulfide bonds
Answer: C: Reduce disulfide bonds 
Explanation: Ans. C. Reduce disulfide bondsb-mercaptoethanol reduces disulfide bonds. Identification of C-terminus is by Carboxypeptidase C or Y which cleaves any C-terminal amino acid, carboxypeptidase B cleaves only Arg or Lys, carboxypeptidase A does not cleave Arg, Lys, or Pro. Denaturation is disruption of protein structure by adding chemicals or acidic or alkaline reagents, heat etc.