Effect of ethanol on the kinetics of rat brain (Na+ + K+) ATPase and K+-dependent phosphatase with different alkali ions.

Abstract (Na + + K + )-dependent ATPase [(Na + K)-ATPase] and K + -dependent p -nitrophenyl phosphatase [pNPPase] activities in rat brain heavy microsomal fractions were studied in the presence of 120 mM Na + and varied concentrations of K + , Rb + , Cs + , Li + or NH 4 + . Scatchard and Hill plots indicated non-hyperbolicity (cooperativity) with all except Li + , which supported a considerably lower activity than any of the other ions tested. Addition of 0.22 M ethanol to the incubation mixtures produced a formally competitive inhibition of ATPase activity with K + , Rb + and Cs + , a non-competitive inhibition with Li + , and a mixed inhibition with NH 4 + . The changes in pNPPase activity generally followed a similar but less clear-cut pattern. The values of the Hill constants were not changed for either enzyme activity. The findings are interpreted as evidence that ethanol inhibits ATPase activity by inducing conformational changes which alter the consequences of ion binding to the various receptor sites.