p-Nitrophenylphosphatase activity catalyzed by plasma membrane (Ca(2+) + Mg(2+)ATPase: correlation with structural changes modulated by glycerol and Ca(2+).

ABSTRACT

The plasma membrane (Ca(2+) + Mg(2+))ATPase hydrolyzes pseudo-substrates such as p-nitrophenylphosphate. Except when calmodulin is present, Ca(2+) ions inhibit the p-nitrophenylphosphatase activity. In this report it is shown that, in the presence of glycerol, Ca(2+) strongly stimulates phosphatase activity in a dose-dependent manner. The glycerol- and Ca(2+)-induced increase in activity is correlated with modifications in the spectral center of mass (average emission wavenumber) of the intrinsic fluorescence of the enzyme. It is concluded that the synergistic effect of glycerol and Ca(2+) is related to opposite long-term hydration effects on the substrate binding domain and the Ca(2+) binding domain.