Mercury blocks Na-K-ATPase by a ligand-dependent and reversible mechanism.
An inhibitory receptor for cardioactive steroids such as digoxin and ouabain is located at the extracellular surface of the Na-K-adenosinetriphosphatase (ATPase) molecule. Besides cardioactive steroids, mercury is a potent inhibitor of the Na-K-ATPase activity. The half-maximal inhibitory concentration (IC50), determined within 30 min at 37 degrees C at 1 microgram protein/ml, was 200 nM, despite the presence of 1 mM EDTA; the IC50 decreased with increasing protein/inhibitor ratio, and it reached 2.7 microM at 0.1 mg protein/ml and 20 microM at 1 mg protein/ml. The IC50 for Na-K-ATPase inhibition by the diuretic compound mersalyl was 4 and 5 microM for the nondiuretic p-chloromercuribenzenesulfonic acid at 0.1 mg protein/ml. The IC50 for HgCl2 inhibition was modulated by the presence of EDTA as well as by the pump ligands Mg, Na, K, and ATP. The E2 conformation of the Na-K-ATPase molecule was more sensitive to HgCl2 than the E1 conformation. The mercury antidote 2,3-dimercapto-1-propanesulfonic acid was able to reactivate approximately 70% of the blocked enzyme. In conclusion, a metal-binding domain of the Na-K-ATPase molecule with particular high affinity for Hg(II) was described functionally in the present work. Therefore Na-K-ATPase belongs to the metal-binding proteins. Metals may modulate the cellular expression and activity of the system by interacting with its metal-binding interface.
Anner
B M
BM
Department of Pharmacology, Geneva University Medical Center, Switzerland.
Moosmayer
M
M
Imesch
E
E
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D004347:Drug Interactions; D004492:Edetic Acid / Q000494:pharmacology; D007527:Isoenzymes / Q000037:antagonists & inhibitors; D008024:Ligands; D008274:Magnesium / Q000494:pharmacology; D008627:Mercuric Chloride / Q000494:pharmacology; D008628:Mercury / Q000494:pharmacology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*; D013438:Sulfhydryl Compounds / Q000494:pharmacology
D007527:Isoenzymes; D008024:Ligands; D013438:Sulfhydryl Compounds; D008627:Mercuric Chloride; D000255:Adenosine Triphosphate; D004492:Edetic Acid; D000254:Sodium-Potassium-Exchanging ATPase; D008628:Mercury; D008274:Magnesium