MERCURY WEAKENS MEMBRANE ANCHORING OF NA-K-ATPASE

The presence of circulating inhibitors able to decrease the renal Na-K-adenosinetriphosphatase (ATPase) activity (natriuretic hormones) was postulated some 30 years ago. In the present work, the natriuretic inhibitor HgCl2 was selected as a model compound for the structural characterization of a possible natriuretic pathway for Na-K-ATPase modification. The structural effects of Na-K-ATPase inhibition by HgCl2 were assessed by trypsinolysis of the blocked enzyme in comparison with untreated preparations. The results show that inactivation of Na-K-ATPase by HgCl2 leads to the release of the alpha-subunit from the membrane preferentially in the E2 conformation but also in the E1 conformation. Apparently, HgCl2 weakens the membrane anchoring of the alpha-subunit, presumably by loosening the alpha-beta-subunit interaction. By this mechanism, the sensitivity of the Na-K-ATPase to extracellular drugs, hormones, and antibodies, as well as to intracellular proteases and other regulatory factors, could be altered.