[Electron transfer in hemoproteins. VI. The dependence of the reduction rate of ferricytochrome c by oxymyoglobin on ionic strength].

The rate of the redox-reaction between MbO2 and ferri-Cyt c has been investigated in the pH range 5-8 under different ionic strength of the solution. The influence of various anions-phosphate, chloride, sulfate and acetat on the rate of the reaction were also studied. It has been shown that under the low ionic strength, I less than 0.1, all pH-dependence curves have pronounced maximum near pH 6.0. While the ionic strength values increase in this interval the reaction rate falls markedly, the profile of lg k versus square root of I/1 + square root of I is linear. Under high ionic strength values, I greater than 0.1, the reaction rate in MbO2-Cyt c system is only slightly influenced by increasing salt concentrations and by pH changing. The results obtained support the idea that the local interactions of charged groups in " active sites" of MbO2 and Cyt c play the most important role in the mechanism of electron transfer. On the contrary net charges of the molecules have a negligible effect on the rate of the reaction. Compared to anions Cl-, SO42- and CH3COO- which influence the reaction rate in an analogous way, phosphate ions have essential inhibiting effect. This is most likely explained by the specific bonding of the phosphate ions to Cty c in the immediate vicinity from the site of the "active contact" with Mb molecule.