Two-electrode voltage-clamp analysis of Na,K-ATPase asparagine 776 mutants.
SourceAnnals of the New York Academy of Sciences, 986, (2003), pp. 150-154
Article / Letter to editor
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Annals of the New York Academy of Sciences
SubjectUMCN 5.4: Renal disorders
Steady-state and pre-steady-state currents of Asn(776) mutants of Na,K-ATPase are presented. The stationary current generated by N776Q strongly depends on the membrane potential, but has a negative slope, opposite to that of the wild-type enzyme. The apparent rate constant of the reaction sequence E(1)P(Na(+)) <--> E(2)P + Na(+) of this mutant is rather independent of the membrane potential and is at resting and depolarizing membrane potential higher than that of the wild-type enzyme. Thus, the voltage-dependent increase of the rate coefficient of the wild type that is associated with extracellular Na(+) rebinding is almost absent in the N776Q mutant. These findings indicate that dislocating the carboxamide group of Asn(776) decreases the affinity of sodium at its extracellular binding site.
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