Potential-dependent surface denaturation of BSA in acid media

In contrast to previous reports claiming bovine serum albumin (BSA) denaturation at mercury surfaces, recently it has been shown that BSA and other proteins do not denature as a result of adsorption to the mercury electrodes at alkaline and neutral pH values. In this pH range, constant current chronopotentiometry (CPS) with mercury or solid amalgam electrodes can be used to distinguish between native, denatured and damaged BSA. Here we show that at acid pH values (around pH 4.5) native and denatured BSA yield almost the same CPS responses suggesting denaturation of native BSA at the electrode surface. Under these conditions BSA is, however, not denatured at the electrode at accumulation potentials (E(A) values) close to the potential of zero charge, but at E(A) values more negative than -0.8 V, after destabilization of the surface-attached BSA by electroreduction of some disulfide groups at about -0.48 V and by electric field effects at more negative potentials.