6. (i) What is the major function of the protein disulfide isomerase (PDI) during protein folding? PDI rapidly covers inactive Ribonuclease A into the active form, whereas it inactivates insulin. What does it imply about their amino acid sequences? (ii) If a peptide bond does NOT show a double bond character, then what would be the problem in protein conformation? ( 1 + 2 ) + 2 = 5 .