p-nitrophenylphosphatase activity catalyzed by plasma membrane (Ca2++Mg2+)ATPase: Correlation with structural changes modulated by glycerol and Ca2+

The plasma membrane (Ca2+ + Mg2+)ATPase hydrolyzes pseudo-substrates such a s p-nitrophenylphosphate. Except when calmodulin is present, Ca2+ ions inhi bit the p-nitrophenylphosphatase activity. In this report it is shown that, in the presence of glycerol, Ca2+ strongly stimulates phosphatase activity in a dose-dependent manner. The glycerol- and Ca2+-induced increase in act ivity is correlated with modifications in the spectral center of mass (aver age emission wavenumber) of the intrinsic fluorescence of the enzyme. It is concluded that the synergistic effect of glycerol and Ca2+ is related to o pposite long-tern: hydration effects on the substrate binding domain and th e Ca2+ binding domain.