Association of basal ATPase activity and cholesterol with a distinct group of rabbit skeletal muscle microsomal particles

Basal ATPase is readily separated from the Ca²⁺-ATPase of the sarcoplasmic reticulum. The median density distributions of cholesterol and basal ATPase activities are almost identical. Digitonin has been succesfully employed in determining the association of cholesterol with specific vesicles in rat liver microsomal preparations. Treatment of rabbit skeletal muscle microsomal preparations with digitonin alters the density distribution patterns of basal ATPase activity and cholesterol in an identical fashion. Protein distribution displays a less marked change in median density. Enzymic activity associated with calcium transport, measured under differing conditions, is largely unaffected. It is concluded that cholesterol and basal ATPase activity are associated with a distinct group of rabbit skeletal muscle microsomal particles.