A flux ratio analysis of the Post-Albers mechanism of the sodium pump.

A thermodynamically constrained method of flux ratio analysis has been applied to the Post-Albers mechanism of the sodium pump to establish a relationship between the thermodynamic "boundary conditions" for the overall pump reaction and the unidirectional flux ratios for the pump-mediated fluxes of sodium and potassium. This relationship provides an experimental criterion for assessing whether or not the reactions associated with ion binding and dissociation to and from the pump, respectively, are close to equilibrium. Examination of experimental data from the current body of literature indicates that the above criterion is not satisfied for the sodium pump of human red blood cells under normal physiological conditions. On the basis of this result, it is concluded that within the context of a Post-Albers mechanism one or more of the ion binding and dissociation steps are not in rapid equilibrium with other such steps, at least not for the sodium pump of human red blood cells under normal physiological conditions.