Ca(2+)-induced inhibition of sodium pump: noncompetitive inhibition in respect of magnesium and sodium cations.
Calcium inhibits the activity of the (Na+/K+)-ATPase from dog kidney in a dose-dependent manner. Other 2A group cations of the periodic table such as Sr2+ and Ba2+ were able to inhibit the ATPase activity but to a lesser degree. Any considerable competition between Ca2+ (Ba2+, Sr2+) ions and magnesium or sodium ions could not be detected using enzyme kinetic analysis. Thus, the above three inhibitory acting ions depress the ATPase activity of sodium pump by interaction with loci distant from the sodium and potassium binding sites. This suggests that the (Na+/K+)-ATPase molecule contains an inhibitory acting binding site for calcium. This putative binding site could recognize magnesium ions as well as calcium, strontium and barium ions. The specificity of the binding site may describe herein be secured by a structure complementary to the coordination structure of Ca2+, Ba2+ and Sr2+ ions characterized by coordination number 8. Mg2+ ions can form coordination structure with a maximum coordination number 6, and do not interact specifically with this binding site.
Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Bratislava, Slovakia.
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Breier
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Sulová
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Vrbanová
D000818:Animals; D001665:Binding Sites; D055592:Biophysical Phenomena; D001703:Biophysics; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D004285:Dogs; D066298:In Vitro Techniques; D007679:Kidney Medulla / Q000201:enzymology; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism
D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D002118:Calcium