STUDY OF ELECTRON-TRANSFER IN HEMOPROTEIN S - APPLICABILITY OF THE MODELS OF INTERMOLECULAR ELECTROSTATIC INTERACTIONS TO IONIC-STRENGTH DEPENDENCES OF THE RATES OF REACTIONS BETWEEN MYOGLOBIN AND CYTOCHROME-C

The nonlinear regression method was used for the evaluation of applica bility of the known model equations that describe Be ionic strength de pendence of the rate of reaction between charged molecules to the elec tron transfer reaction between myoglobin and cytochrome c. The full an d simplified equations of Bronsted-Debay-Hukkel and Wherland-Gray equa tion, as well as equations, derived from models al complementary inter actions and <<parallel disks>> were used. The experimental dependences of reaction rate on ionic strength all all pH values in the pH interv al 5-8 have a negative slope which corresponds to opposite charges of reacting particles and does not correspond (even in sign) to the total charges of Mb and Cyt c. It is found that all models considered, exce pt for those of complementary interactions, permit a satisfactory desc ription of the experimental data. In the case of <<parallel disks>> an d Bronsted-Debay-Hukkel equations, however, the optimal values of Z(1) Z(2) and R(1)=R(2)=R do not correspond to the real size of the Mb-Cyt c electron transfer complex and to the radii and charges at their cont act sites found from the experiment, The Wherland-Gray equation allows the best approximation of the experimental ionic strength dependences assuming that Z(1)Z(2) and R(1)=R(2)=R are some effective parameters that reflect the protein field distribution in the contact site. This distribution can be approximated as a monopole with parameters not coi nciding with the parameters of the protein.