SPECTROSCOPIC AND ELECTROCHEMICAL STUDIES ON THE 4-ALPHA-HELICES BUNDLE CYTOCHROME-C'

The cyclic voltammogram of the cytochrome c' from Achromobacter xyloso xidans NCIB 11015 displayed a quasi-reversible electron-transfer proce ss and the observed half-wave peak potential was estimated to be E(1/2 ) = 184 mV vs NHE. The redox potential of cyt c'(Fe3+ / Fe2+) decrease s with increasing buffer concentration, implying that the oxidized sta te of the protein is stabilized by counter anion shielding of the posi tive charges on the protein surface. The intensities of the magnetic c ircular dichroism (MCD) spectra of the protein at lambda = 402 and 418 nm decrease with increasing ionic strength. The decreasing of the MCD intensity at high ionic strength indicates the increasing of the high -spin state species. These results suggest that the structural change of the solvent exposed charged amino acid residues linking to outside of the protein might allow the regulation of the electron-transfer rea ction of cytochrome c'.