Effect of chemical modification of cytoplasmic activator protein on human red cell membrane Ca++ + Mg+ ATPase.

A highly purified cytoplasmic activator protein of human red cell membrane Ca⁺⁺ + Mg⁺⁺ ATPase was prepared by two step purification scheme utilizing Diethylaminoethyl cellulose (DE-52) and sephadex (G-100) column chromatography. This purified protein can elicit a maximum activation of membrane Ca⁺⁺ + Mg⁺⁺ ATPase at low calcium concentrations. The stimulatory effect of this protein can be rendered totally ineffective by chemical modification with N-bromosuccinimide. The results suggest a possible role of methionine oxidation in the regulation of the Ca⁺⁺ + Mg⁺⁺ ATPase activator activity.