The Na+/e− stoichiometry of the Na+‐motive NADH : quinone oxidoreductase in Vibrio alginolyticus

A method is proposed to estimate the stoichiometries of primary Na+-pumps in intact bacterial cells. It is based on technique when the H+/e- stoichiometry is measured in the presence of protophorous uncoupler and in the absence of penetrating ions other than H+. Under these conditions, the H+ influx discharges membrane potential generated by the Na+ pump so the Na+/e- and H+/e- ratios become equal. Using this approach it is shown that the Na+/e- ratio for the Na+-motive NADH:quinone oxidoreductase of Vibrio alginolyticus is equal to 0.71 +/- 0.06. The Na+/e- stoichiometry appears to be approximately 1, provided that the contribution of the non-coupled NADH:quinone oxidoreductase, which is resistant to low HQNO concentrations, is taken into account.