Comparative Kinetic-Ionic Strength Study of Two Differently Charged Cytochromes C: Effects are Limited to Overall Charge
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Biochemical and Biophysical Research Communicatsions
The reduction kinetics of two differently charged cytochromes c, horse cytochrome c and Rhodosprillum rubrum cytochrome c2, by ferrous EDTA2− were studied as a function of ionic strength. Since both proteins have nearly the same heme edge region, but have very different overall surface charge, this comparative study served as a direct test of the utility of small nonbinding non-physiological redox agents in the study of the charge of electron transfer sites of redox proteins. Calculations based on the ionic strength-kinetic data yielded protein charges of +10 and +2.3 for cytochrome c and cytochrome c2 respectively and compared well with values of +9 and +3 for the overall charge of the proteins based on acidic and basic amino acid residues. It is concluded that ionic strength effects upon the redox kinetics with such nonbinding nonphysiological redox agents reflect the influence of the overall protein charge and not the localized charge of the presumed site of electron transfer.