[Effect of the structural integrity of Na,K-ATPase preparations on the ability of lithium to substitute for sodium in enzyme activation].

: The ability of Li+ to substitute for Na+ in activating ouabain-sensitive ATPase of the rat kidney was studied on three kinds of the enzyme preparation: a) crude membrane fraction, b) purified enzyme, c) tissue slices. The preparations were free of endogenous Na+ and K+. The ATPase activity of slices was estimated both biochemically and cytochemically. In slices, the extent of Li+--Na+-isomorphism was about 10-fold higher than that in the purified enzyme. It is concluded that the biochemical procedures involved in the enzyme isolation procedure cause the damage of membranes, thus decreasing Li+-affinity to the Na+-dependent site.