Chemical aspects of the influence of cobalt ions on ATPase activity

Abstract

The influence of Co2+ ions on the activities of Na+/K+-ATPase and Mg2+-ATPase, enzymes from rat brain synaptic plasma membrane, was studied. The aim of this study was to investigate the inhibition of both ATPases activities by exposure to cobalt ions as a function of experimentally added CoSO4. The free Co2+ concentrations in the reaction mixture were also calculated and discussed. CoSO4 induced a dose-dependent inhibition of both enzymes. The IC50 values of Co2+, as calculated from the experimental curves, were 168 mu M for Na+/K+-ATPase and 262 mu M for Mg2+-ATPase, and for the recalculated free Co2+ concentration 75.4 mu M for Na+/K+-ATPase and 136 mu M for Mg2+-ATPase. The obtained linear Dixons plot for Na+/K+-ATPase implies equilibrium binding of cobalt with inhibitory sites on the enzyme. The kinetic parameters for both enzymes in presence and absence of CoSO4 were calculated from the experimental data. The results of the kinetic analysis show that inhibition of Na+/K+-ATPase induced by CoSO4 is non-competitive, and for Mg2+-ATPAse that there are two sites of different sensitivities or two different enzymes.