Protein chemistry — During the reconstitution of native insulin from its separate A and B polypeptide chains, which reagent pair is used in sulfitolysis/renaturation workflows to enable correct disulfide bond formation between the chains?

Introduction / Context:Insulin consists of two chains (A and B) linked by two inter-chain disulfide bonds and one intra-chain disulfide in the A chain. Classic chemical synthesis and some recombinant workflows generate individual chains that must be recombined to form the correct native disulfide pattern. Sulfitolysis chemistry is widely used to protect cysteines as S-sulfonates and then allow controlled reformation of disulfide bonds upon renaturation.

Given Data / Assumptions:

• Separate A and B chains require correct pairing via disulfide bonds for biological activity.
• Sulfitolysis creates S–SO3− (S-sulfonate) derivatives to prevent incorrect disulfide scrambling.
• Reagents such as sodium sulphite and related disulfonate/tetrathionate partners enable reversible protection and subsequent oxidative refolding.

Concept / Approach:Identify the reagent pair associated with sulfitolysis and disulfide reformation, rather than inert salts. Sodium sulphite participates in adding sulfonate groups to cysteine thiols; sodium disulphonate (tetrathionate-like partner) drives the reversible modification and later assists in oxidative coupling to re-form native disulfide architecture during chain combination.

Step-by-Step Solution:

Verification / Alternative check:Historical insulin reconstitution protocols employ sulphite/disulfonate systems (analogous to sulphite/tetrathionate) to minimize mispairing and maximize yield of bioactive insulin.

Why Other Options Are Wrong:

Common Pitfalls:Confusing disulfide bond formation reagents with denaturants or simple salts; proper redox buffering is essential for correct pairing.

Final Answer:Sodium disulphonate and sodium sulphite.