title: The effect of ionic strength on the electron-transfer rate of surface immobilized cytochrome C.
abstract: Horse heart cytochrome c was immobilized on four different self-assembled monolayer (SAM) films. The electron tunneling kinetics were studied in the different assemblies as a function of the ionic strength of the buffer solution using cyclic voltammetry. When cytochrome c is electrostatically immobilized, the standard electron exchange rate constant k0 decreases with the increase of the solution's ionic strength. In contrast, the protein covalently attached or ligated has a rate constant independent of the ionic strength. The inhomogeneity of electrostatically immobilized cytochrome c increases with the increase of the solution's ionic strength whereas that of the covalently attached protein is independent of the ionic strength. A comparison of these different electron-transfer behaviors suggests that the thermodynamically stable geometry of cytochrome c in the electrostatic assemblies is also an electron transfer favorable one. It suggests that the surface charges of cytochrome c are capable of guiding it into geometries in which its front surface faces the electron-transfer partner. The inhomogeneity observed in this study indicates that a distribution of cytochrome c orientations and thus a distribution of electron transfer rate constants exists.
authors.affiliation: Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA.
authors.forename: Hongjun
authors.initials: H
authors.lastname: Yue
authors.forename: David H
authors.initials: DH
authors.lastname: Waldeck
authors.forename: Jelena
authors.initials: J
authors.lastname: Petrović
authors.forename: Rose A
authors.initials: RA
authors.lastname: Clark
mesh_terms: D000818:Animals; D045304:Cytochromes c / Q000737:chemistry*; D004583:Electrons; D004800:Enzymes, Immobilized / Q000737:chemistry*; D006736:Horses; D007477:Ions; D008954:Models, Biological; D008958:Models, Molecular; D055672:Static Electricity; D013499:Surface Properties
chemical_list: D004800:Enzymes, Immobilized; D007477:Ions; D045304:Cytochromes c