Cyclic voltammetry and 1H-NMR of Rhodopseudomonas palustris cytochrome c2. Probing surface charges through anion-binding studies.
The effects of increasing concentrations of Cl-, ClO4-, and HCO3- on the redox potential of Rhodopseudomonas palustris cytochrome c2 indicate that the two polyatomic anions bind specifically to the protein at one site, while chloride simply exerts an ionic atmosphere effect. The change in E degree upon specific anion binding allows us to probe for the influence of surface charges on the redox potential of cytochromes c. The decrease in redox potential at null ionic strength (delta E degree I = 0) due to anion neutralization of one positive surface charge was found to be 23 mV with perchlorate and 33 mV with bicarbonate. These values compare reasonably well with previous theoretical predictions and estimates of the effect of charge alteration on the E degree values in cytochromes c chemically modified or mutated at surface lysines. These delta E degree values, determined on the unmodified protein, are unprecedented for c-type cytochromes. The anion-induced chemical shift changes of the hyperfine-shifted heme 1H-NMR resonances of the oxidized protein yield lower limit values of 53 M-1 and 18 M-1 for the affinity constant for specific HCO3- and ClO4- binding, respectively.
Battistuzzi
G
G
Department of Chemistry, University of Modena, Italy.
Borsari
M
M
Dallari
D
D
Ferretti
S
S
Sola
M
M
D000838:Anions; D001665:Binding Sites; D003574:Cytochrome c Group / Q000737:chemistry*; D045362:Cytochromes c2; D004563:Electrochemistry; D009682:Magnetic Resonance Spectroscopy; D009994:Osmolar Concentration; D010084:Oxidation-Reduction; D012241:Rhodopseudomonas / Q000737:chemistry*
D000838:Anions; D003574:Cytochrome c Group; D045362:Cytochromes c2