[Solubility of the Mg2+-dependant Ca2+-activated ATPase fraction of the plasma membranes of synaptosomes].

Mg2+-dependent Ca2+-activated ATPase (Mg2+,Ca2+-atpase, EC 3.61.4) in the fraction of synaptosome plasmatic membranes is activated with 0.05-0.08% solutions of digitonin and sodium deoxycholate. At higher concentrations of digitonin the activating effect lowers, sodium deoxycholate in the increasing concentrations inactivates the enzyme. 0.08% digitonin activates Mg2+,Ca2+-ATPase of synaptosome membranes, without demanding for its transition into solubilized state. Separation of non-active 0.08% digitonin extract from the deposit results in a decrease in the enzymatic activity of the latter and addition of the extract to the deposit activates the enzyme. At least two components separable from each other are likely to be necessary for the enzyme activity manifestation. A solubilized preparation of Mg2+,Ca2+-ATPase with the maximum activity and the ratio of total ATPase to Mg2+-ATPase equal to 3.5-4.0 may be obtained by extraction with 0.15-0.20% digitonin solution. Maximum quantily of protein is extracted by means of digitonin in the same concentrations. The extracted protein is divided in 7.5% polyacrylamide gel into eight-ten electrophoretic zones.