Characterization of a partially purified Na+,K+-ATPase from dog heart

Ouabain-sensitive Na+,K+-ATPase of isolated membranes represents a biochemical correlate of the "Na+ pump" that is present in intact tissue and is responsible for dissimilar distributions of Na+ and K+ across cellular plasma membranes. The enzyme has been purified from a variety of sources and its properties have been reported. Only a limited number of studies, however, deal with the cardiac Na+,K+-ATPase. We solubilized this enzyme from dog heart with deoxycholate and effected its further purification by NaI treatment. The method yielded an enzyme preparation of high specific activity (140 mumole/mg protein per hr). The following characteristics were noted: (1) pH optima of 7.4 and greater than 9.0 for ouabain-sensitive and -insensitive ATPases; (2) inhibition by Ca2+ and ouabain, the latter effect being allosteric in nature; (3) inhibition by sulfhydryl reagents (N-ethylmaleimide, p-chloromercuribenzoate) of the ouabain-sensitive ATPase but not of the -insensitive enzyme activity. All these properties resembled those seen in isolated plasma membranes (sarcolemma), suggesting that the purification procedure did not alter the properties of mono- and divalent interacting sites as well as a digitalis recognition domain of the Na+ pump. These results thus aid in further understanding the regulation of this vectorial pump that is critical in myocardial function.