[Some properties of Mg 2+, Ca 2+-AtPase of brain microsomal fractions and synaptic plasma membranes in the solubilized state]

Digitonin-solubilized Mg2+, Ca2+-ATPases of the brain microsomal fraction and synaptic plasma membranes are activated against a background of 6.0 mM Mg2+ by 0.001 and 0.03 mM of the added Ca2+ and manifest maximum activity at temperatures or 40-45 and 35-42 degrees C, respectively. The enzymes of the initial membrane preparations are activated by the same concentrations of the added Ca2+ and are characterized by the same temperature dependence. The values of pH-optima of the enzyme activity of both solubilized preparations are 7.0-7.3 and in comparison with pH-dependence of the initial membrane preparations are shifted towards acid side.