Properties of the sarcolemmal calcium ion-stimulated adenosine triphosphatase of hamster skeletal muscle

Abstract

1. A sarcolemmal fraction was isolated from hamster hind-leg skeletal muscles by successive treatment with lithium bromide and potassium chloride. The membranous fraction was observed to contain a highly active Ca²⁺-stimulated ATPase (adenosine triphosphatase), a Mg²⁺-stimulated ATPase, and an Na⁺+K⁺-stimulated Mg²⁺-dependent ouabain-sensitive ATPase. 2. The Ca²⁺-stimulated ATPase activity was pH-dependent, the optimum being pH7.6. 3. Optimum activation of this enzyme was obtained with 3–4mm-Ca²⁺ when 4mm-ATP was present as a substrate, and was not influenced by Na⁺, K⁺ or ouabain, whereas 2,4-dinitrophenol, sodium azide, oligomycin, sodium fluoride and ethanedioxybis(ethylamine)tetra-acetate were inhibitory. 4. The Ca²⁺-stimulated ATPase was markedly inhibited by thiol-blocking reagents, and cysteine was able to reverse this inhibition. 5. Various bivalent cations stimulated ATP hydrolysis by the sarcolemmal fraction in the following decreasing order of potency: Mg²⁺, Ca²⁺, Mn²⁺, Co²⁺, Sr²⁺, Ba²⁺, Zn²⁺, Cu²⁺.