Modulator binding protein antagonizes activation of (Ca2+ + Mg2+)-ATPase and Ca2+ transport of red blood cell membranes

Red blood cells contain a protein that activates membrane-bound (Ca²⁺ + Mg²⁺)-ATPase and Ca²⁺ transport. The red blood cell activator protein is similar to a modulator protein that stimulates cyclic AMP phosphodiesterase. Wang and Desai [Journal of Biological Chemistry 252:4175–4184, 1977] described a modulator-binding protein that antagonizes the activation of cyclic AMP phosphodiesterase by modulator protein. In the present work, modulator-binding protein was shown to antagonize the activation of (Ca²⁺ + Mg²⁺)-ATPase and Ca²⁺ transport by red blood cell activator protein. The results further demonstrate the similarity between the activator protein from human red blood cells and the modulator protein from bovine brain.