Erythrocyte membrane anion-sensitive Mg 2+-ATPase—Identity with monovalent cation sensitive Ca 2+-Mg 2+-ATPase

Abstract

1. 1. Activation of Mg 2+-ATPase of rabbit and guinea-pig erythrocyte membrane by bicarbonate or chloride could be completely abolished by ethylene-glycol-bis-(β-aminoethylether)- N, N'-tetraacetic acid. The anion stimulation was actually an activation of contaminating Ca 2+ -stimulated Mg 2+-ATPase by monovalent cations associated with the anions. 2. 2. Guinea-pig red cell Ca 2+-Mg 2+-ATPase could be activated by both sodium and potassium while the rabbit enzyme was sensitive only to sodium. The concentrations of monovalent cations for half-maximal stimulation of Ca 2+-Mg 2+-ATPase are: k na+ = 40.8 mM, k k+ = 12.2 mM (guinea-pig); K Na+ = 13.3mM (rabbit). 3. 3. Potassium enhanced activation of rabbit erythrocyte membrane Ca 2+-Mg 2+-ATPase by red cell Ca 2+-Mg 2+-ATPase activator protein. With the guinea pig enzyme, neither sodium nor potassium enhanced activator stimulation of Ca 2+-Mg 2+-ATPase. 4. 4. Ca 2+-Mg 2+-ATPase of aged rabbit erythrocyte membrane responded to sodium but not to activator protein. 5. 5. Triton X-100 solubilized rabbit erythrocyte membrane Ca 2+-Mg 2+-ATPase has an apparent molecular weight of 371,000. It did not respond to the activator. 6. 6. One major and three minor proteins, visualized by SDS-polyacrylamide gel electrophoresis, were extracted from rabbit erythrocyte membrane by 50 μM chlorpromazine.