APPLICABILITY OF THE MODELS OF INTERMOLEC ULAR ELECTROSTATIC INTERACTIONS TO IONIC-STRENGTH DEPENDENCIES OF THE REACTION-RATES BETWEEN MYOGLOBIN AND CYTOCHROME-C

The nonlinear regression method was used for the evaluation of applica bility of the known model equations (Wherland-Gray, Bronsted-Debay-Huk kel and <<parallel disks>>) which describe the ionic strength dependen ce of the reaction rate between charged molecules to the redox reactio n of cytochrome c with sperm whale myoglobin modified at His 12(A10) w ith the bromoacetate spin label, and pig myoglobin. Unlike the native sperm whale Mb studied earlier [1],the objects chosen have monotonous pH-dependence of the reaction rate and are more simple with regards to electrostatic interactions in the electron-transfer complex. This all owed to study the influence of the total as well as the local protein charge on the correspondence of the ion strength dependencies to the t heoretical models and optimal parameters of the equations. It was show n that the models considered, as in the case of the native sperm whale Mb-Cyt c reaction, permit satisfactory description of the experimenta l data, but the obtained parameters cannot be applied to the whole pro teins or their contact sites. In the best case (Wherland-Gray equation ) it is possible to do if the distribution of electrostatic potential in the contact area is considered. The reason can be that, unlike othe r protein redox-systems, the contact sites of both Mb and Cyt c have t he charged residues of both signs, and the His GH1 residue located in the contact Mb site is not only involved in the electrostatic interact ions in electron-transfer complex, but also participates directly in t he mechanism of charge transfer.