[Solubilization of Mg2+-dependent Ca2+-activated ATPase of brain microsome fraction]

Mg2+-dependent Ca2+-activated ATPase (Mg2+, Ca2+-ATP-ase) of microsome fraction from grey matter of great cerebral hemispheres of cattle is activated by 0.1% solution of digitonin. Simultaneously 30-60% of initial fraction protein is extracted, respectively, with 0.1-0.3% concentrations of digitonin. The Mg2+- and Mg2+, Ca2+-ATPase activities manifest in solubilized protein. The maximal solubilization of both enzymes is reached when treating the fraction of brain microsomes with 0.3% solution of digitonin, the Mg2+, Ca2+-ATPase activity is not manifested in the 0.2% digitonin extract of this fraction. The Mg2+, Ca2+-ATPase activity is not always manifested in the 0.4% digitonin extract of the sediment which was obtained after extracting the initial fraction with 0.2% solution of digitonin. Addition of 0.2% extract to it causes manifestation or increase of the Mg2+, Ca2+-ATPase activity. Thus, minimum two components which are extracted by detergent in different concentrations or one of the extracted components which is an activator of solubilized Mg2+, Ca2+-ATPase may be necessary for manifestation of this activity in the solubilized components of the fraction of brain microsomes. The membrane components extracted with digitonin possess evidently a small molecular weight as they compose 7.5% polyacrylamide gel in which 0.4% digitonin extract of the brain microsome fraction is divided into 7-8 electrophoretic zones.