Mechanism of the Na,K-ATPase inhibition by MCS derivatives.
The previously reported class of potent inorganic inhibitors of Na,K-ATPase, named MCS factors, was shown to inhibit not only Na,K-ATPase but several P-type ATPases with high potency in the sub-micromolar range. These MCS factors were found to bind to the intracellular side of the Na, K-ATPase. The inhibition is not competitive with ouabain binding, thus excluding its role as cardiac-steroid-like inhibitor of the Na,K-ATPase. The mechanism of inhibition of Na,K-ATPase was investigated with the fluorescent styryl dye RH421, a dye known to report changes of local electric fields in the membrane dielectric. MCS factors interact with the Na,K-ATPase in the E(1) conformation of the ion pump and induce a conformational rearrangement that causes a change of the equilibrium dissociation constant for one of the first two intracellular cation binding sites. The MCS-inhibited state was found to have bound one cation (H(+), Na(+) or K(+)) in one of the two unspecific binding sites, and at high Na(+) concentrations another Na(+) ion was bound to the highly Na(+)-selective ion-binding site.
Stimac
R
R
Department of Biology, University of Konstanz, Konstanz, Germany.
Kerek
F
F
Apell
H-J
HJ
D000818:Animals; D000252:Calcium-Transporting ATPases / Q000737:chemistry; D017554:Carbon Compounds, Inorganic / Q000494:pharmacology*; D003198:Computer Simulation; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005753:Gastric Mucosa / Q000201:enzymology; D006863:Hydrogen-Ion Concentration; D007679:Kidney Medulla / Q000201:enzymology; D016658:Psoas Muscles / Q000201:enzymology; D011817:Rabbits; D051381:Rats; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*
D017554:Carbon Compounds, Inorganic; D004791:Enzyme Inhibitors; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase