(Mg 2+ + K +)-Dependent inhibition of NaK-ATPase due to a contaminant in equine muscle ATP

Abstract

Summary A contaminant present in commercial ATP isolated from equine muscle induces a (Mg2+ + K+)-dependent inhibition of human red cell NaK-ATPase (EC 3.6.1.3). This inhibition is completely reversed by isoproterenol (1 mM). The contaminant (inhibitor) is essentially lacking in ATP prepared synthetically by phosphorylation of adenosine. A procedure is described for separation of the inhibitor from equine muscle ATP with strongly acidic cation exchange resin. In the presence of isolated inhibitor, a (Mg2+ + K+)-dependent inhibition of NaK-ATPase can be demonstrated with synthetic ATP as the substrate.