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

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.