Electrochemical Oxidation and Reduction of Ferredoxin Adsorbed on Mercury Electrode Surface. Phase-selective A. c. Polarography at DME

Abstract

Abstract The electrochemical behavior of Clostridium pasteurianum ferredoxin (Cl.Fd) was studied by a.c. polarography with the dropping mercury electrode. The a.c. polarograms observed in acidic media (pH<7) were assigned to RSH/RSHg redox reaction of the cysteine residues of apoferredoxin, whereas those observed in basic media (pH>8) were assigned to a two-step one-electron transfer (EE mechanism) to the iron-sulfur clusters of Cl.Fd adsorbed on the mercury electrode surface ((Cl.Fd)ad). The a.c. polarographic behavior of (Cl.Fd)ad observed in basic media was interpreted by theory of a.c. polarography of a two-step surface redox reaction. The formal standard oxidation-reduction potential of (Cl.Fd)ad was determined to be −0.33 V vs. NHE at pH 7.0, and its pH dependence was −30 mV/pH between pH 8 and 10.