Calcium-dependent inhibition of the erythrocyte Ca2+ translocating ATPase by carbodiimides.

The ATP hydrolytic activity of the solubilized and purified Ca2+-translocating ATPase from human erythrocyte plasma membrane was strongly inhibited by the nonpolar compound, N,N'-dicyclohexylcarbodiimide, both in the presence and in the absence of calmodulin. However, the more water-soluble carbodiimides, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 1-cyclohexyl-3-(2-morpholinoethyl)carbodiimide had little inhibitory effect on the enzyme. The inhibitory effect of N,N'-dicyclohexylcarbodiimide was most pronounced at acid pH, and declined sharply at alkaline pH values. In addition, the optimum pH for the enzyme activity also shifted to more alkaline values in the presence of the carbodiimide. Calcium ion appears to favor the inhibition induced by the carbodiimide, in contrast to the observed protection by Ca2+ in the sarcoplasmic reticulum Ca2+-translocating ATPase. N,N'-Dicyclohexylcarbodiimide also dramatically decreased the stimulatory effect of calmodulin on the activity of the enzyme.