Lead affects the formation of the phosphorylated intermediate on the (Ca2+,Mg2+)-ATPase from human erythrocytes

The effect of lead on the (Ca2+,Mg2+)-ATPase (EC 3.6.1.38) of erythrocyte membranes is investigated. The presence of lead in the reaction mixture, depending on the temperature of incubation, causes an important decrease in ATPase activity. The presence of calmodulin also modulates this effect. The results suggest that calmodulin accelerates the dephosphorylation of the phosphorylated intermediates and that lead impedes their formation. Together, the two effects, on the one hand lead preventing the formation of the intermediates, and on the other calmodulin allowing the rapid hydrolysis of the intermediates, would explain employing rapid kinetics, the almost instantaneous deactivation of the enzyme.