Ouabain-Sensitive Mg++-ATPase, K+-ATPase and Na+-ATPase Activities Accompanying a Highly Specific Na+-K+-ATPase Preparation

Abstract

1. An Na⁺-K⁺-ATPase [EG 3.6.1.3] preparation obtained from pig cerebrum microsomes by Nal-treatment has been shown to hy-drolyse ATP in the presence of either K⁺ alone (K⁺-ATPase) or Na⁺ alone (Na⁺-ATPase) when the assay pH was low for the former and high for the latter. 2. K⁺-ATPase activity had the optimum pH at 5.3 when K⁺ concentration was 1 mM. Na⁺-ATPase activity was near maximum when the assay pH was between 7.7 and 9.0 at Na⁺-concentration of 10 mM. 3. Ouabain-sensitive Mg⁺⁺-ATPase activity has been detected with the optimum pH which was nearly the same as that of K⁺-ATPase activity but with a pH-activity curve broader toward alkalinity than that for the latter.