Spectroscopic and Electrochemical Studies on the FOUR-α- Helices Bundle Cytochrome C

Abstract

The cyclic voltammogram of the cytochrome c' from Achromobacter xylosoxidans NCIB 11015 displayed a quasi-reversible electron-transfer process 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⁺) decreases with increasing buffer concentration, implying that the oxidized state of the protein is stabilized by counter anion shielding of the positive charges on the protein surface. The intensities of the magnetic circular dichroism (MCD) spectra of the protein at λ = 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 electrontransfer reaction of cytochrome c'.