LEAD AFFECTS THE FORMATION OF THE PHOSPHORYLATED INTERMEDIATE ON THE (CA2-ATPASE FROM HUMAN ERYTHROCYTES(,MG2+))

The effect of lead on the (Ca2+,Mg2+)-ATPase (EC 3.6.1.38) of erythroc yte membranes is investigated. The presence of lead in the reaction mi xture, depending on the temperature of incubation, causes an important decrease in ATPase activity. The presence of calmodulin also modulate s this effect. The results suggest that calmodulin accelerates the dep hosphorylation of the phosphorylated intermediates and that lead imped es their formation. Together, the two effects, on the one hand lead pr eventing the formation of the intermediates, and on the other calmodul in allowing the rapid hydrolysis of the intermediates, would explain e mploying rapid kinetics, the almost instantaneous deactivation of the enzyme.