ELECTROCHEMICAL INVESTIGATIONS OF THE INTERMOLECULAR ELECTRON-TRANSFER BETWEEN CYTOCHROME-C AND NADPH CYTOCHROME-P450 REDUCTASE

The electron exchange reaction of cytochrome c with NADPH-cytochrome P 450 reductase was investigated electrochemically. For this purpose the electrochemical behavior of cytochrome c in solution, adsorbed or cov alently immobilized on a modified gold electrode surface was studied. In the case when cytochrome c was in solution or only electrostaticall y adsorbed on the electrode surface, fast electron transfer was observ ed with NADPH-cytochrome P450 reductase. When cytochrome c was covalen tly bound to the electrode surface, in spite of quasi-reversible elect ron exchange with the electrode, no electron transfer was observed wit h NADPH-cytochrome P450 reductase. These results suggest that electros tatically adsorbed cytochrome c on the modified electrode surface has some mobility that allows re-orientation as required to interact both with the electrode and with the NADPH-cytochrome P450 reductase. In co ntrast, covalent binding of cytochrome c leads to permanent orientatio n towards the electrode surface and thus blocks the cytochrome c elect ron accepting site from the reductase. (C) 1997 Elsevier Science S.A.