EFFECT OF CHLORPROMAZINE AND GOSSYPOL ON CA2+-ATPASE ACTIVITY IN THE MICROSOMAL-MEMBRANES OF RAT TESTES

The microsomal membranes isolated from rat testes have been found to contain a Mg2+-dependent and a Mg2+-independent Ca2+-ATPase. The enzyme activities were inhibited by two contraceptive drugs-gossypol and chlorpromazine. The inhibition by the former was affected by the presence of ligand (s) and not the substrate in the incubation medium, whereas ligand(s)/substrate did not affect the inhibition by chlorpromazine. This may be explained from the fact that the binding of chlorpromazine and ligand(s)/substrate to the enzyme are independent of each other whereas in case of gossypol the ligand(s) compete with the drug at the binding site of the enzyme.