The electrochemistry of proteins and related substances: Part II. Insulin

The electroreduction of insulin in pH 7.4 solution was studied at the hanging mercury drop electrode by cyclic voltammetry and at a mercury pool electrode by controlled potential coulometry. The proposed mechanism involves reduction of an adsorbed monolayer of insulin (maximum coverage of 10 μC cm^?2) in a four-electron reaction at about ?0.6 V vs. SCE resulting in breakage of two of the three disulfide bonds in the molecule. Fast reoxidation leads to recovery of much of the reduced species. At longer time (ca. 100 s) a steady state is reached where the reductions and reoxidation involve reversible two-electron reactions.