A comparison of the E2P-like states induced by metal-fluoride complexes in the Na,K-ATPase and H,K-ATPase

CENTENO, M. M.; FERREIRA GOMES, M. S.; MONTI, J. L. E.; ROSSI, R. C.; MONTES, M. R.

Sierra de la Ventana

Congreso; SAB 2014; 2014

Sociedad Argentina de Biofísica

Na,K-ATPase and H,K-ATPase are membrane-bound ion pumps that generate electrochemical gradients of cations across the plasma membranes of animal cells fueled by the hydrolysis of ATP. They undergo phosphorylation and dephosphorylation reactionsand oscillate between two major conformations, E1 and E2. Fluorinated complexes of Mg2+, Al3+ and Be2+ inhibit the activity of several ATPases because they imitate the phosphoryl group and stabilize the intermediate ground (BeFx), transition (AlFx) andproduct (MgFx) states in the dephosphorylation sequence: E2-P (ground state) -> E2·P (transition state) -> E2·Pi (product state) -> E2 + Pi. We have studied the kinetics of the E1-> E2P conformational change, assessed by eosin fluorescence measurements, produced by metal-fluorides complexes in the Na,K-ATPase and H,K-ATPase at 25 °C in media with 25 mM imidazole-HCl, pH 7.4. Our results show that BeFx induces the E2-P ground state with a similar rate in both enzymes, while MgFx induces the E2·Pi product state with a much slower rate in the H,KATPase than in the Na,K-ATPase. These results are in agreement with the difficulties reported to isolate the state of the H,K-ATPasecontaining occluded K+.