Kinetic alterations of the divalent cation-dependent ATPase activities of human erythrocyte membranes induced by blocking the membrane amino groups.

Treatment of erythrocyte membrane fragments with the amino group reagent sodium trinitrobenzenesulphonate (TNBS) leads to significant alteration of the kinetic properties of the membrane-bound (Ca2+ + Mg2+) and Mg2+-dependent ATPases, which appear to increase their affinity towards divalent cations and to decrease their maximal rates. Although it has not been possible to ascertain whether the amino groups involved in the TNBS effect belong to the membrane phospholipids or to the ATPase proteins, it appears that such groups play an essential role in the hydrolytic activity of the divalent cation-dependent ATPases, either by affecting the enzymes' microenvironment or by being directly involved in the enzymes'catalytic mechanism.