Divalent cation dependent ATPase activities of red blood cell membranes: Influence of the oxidation of membrane thiol groups close to each other

Abstract

An Mg²⁺-dependent low ATPase activity can be detected in erythrocyte “white membranes,” in addition to that of the well known (Ca²⁺ + Mg²⁺)-ATPase. The thiol oxidizing agent diamide affects both activities. The oxidation of neighboring thiols seems to leave the mechanism of the (Ca²⁺ + Mg²⁺)-ATPase amplification system evoked by Ca²⁺ largely unaffected. The perturbation caused by diamide in the membranes seems to affect primarily a step of the ATP hydrolysis mechanism that is common to both ATPase activities. The effectiveness of diamide seems to be the same when either Ca²⁺ and Mg²⁺, or Mg²⁺ alone are present during the reagent action. Reduction of disulfide bonds by DTE after diamide treatment restores the (Ca²⁺ + Mg²⁺)-ATPase activity but is unable to take the Mg²⁺-ATPase activity back to the original level. The hypothesis is discussed that the redox state of one (or more than one) couple of SH close to each other and possibly connected to the active site, may be an important factor in optimizing the efficiency of Ca action on the (Ca²⁺ + Mg²⁺)-ATPase.