This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Biochemistry
Protein di sulphide isomerase is involved in 
Select and explain. 
A. Protein synthesis, B. Protein degradation, C. Protein folding, D. Protein quaernary structure formation
C: Protein folding
Answer: C: Protein folding 
Explanation: Disulfide bonds between and within polypeptides stabilize teiary and quaternary structures. However, disulfide bond formation is nonspecific. Under oxidizing conditions, a given cysteine can form a disulfide bond with the --SH of any accessible cysteinyl residue. By catalyzing disulfide exchange, the rupture of an S--S bond and its reformation with a different paner cysteine, protein disulfide isomerase facilitates the formation of disulfide bonds that stabilize a protein&;s native conformationPeptidyl cis-trans isomerase, protein disulphide isomerase and chaperones are involved in protein folding