The K+ -activation of the Mg2+ - dependent cycle of Na, K-ATPase

The K⁺ -activation of the Mg²⁺ - dependent cycle of Na, K-ATPase

M. Leladze, E. Nozadze, G. Chkadua and Z. Kometiani

I. Beritashvili Institute of Physiology, Georgian Academy of Sciences, 380060 Tbilisi, Georgia

In the OPM régime (/ATP_free³ 2, MgATP £ 1.85) dephosphorylation of the Mg²+ -bound phosphorylated form of Na, K-ATPase occurs. Under these conditions, the number of Na⁺ -bound sites of essential activating nature is 3 when [K⁺ ] £ 100 mM, and 4 when [K⁺ ] >125 mM. On the other hand, investigation of the K⁺ -dependent stage of dephosphorylation shows that the number of K⁺ -bound activation sites may be 0, 1 or 2. This alteration is not affected by the Na⁺ concentration. However, an increase of Na⁺ concentration changes the K⁺ -affinity of the enzyme. The experimental data show that in the OPM régime ions are essential activators of Na, K-ATPase system.

Keywords: essential activators, Na,K-ATPase, Na -ATPase