Coupling site of the respiration-dependent sodium pump in a psychrophilic bacterium, Vibrio sp. strain ABE-1.

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Abstract
The coupling site of a respiration-dependent primary Na+ pump to the respiratory chain was studied in a psychrophilic bacterium, Vibrio sp. strain ABE-1. Several inhibitory experiments showed that the Na+ extrusion caused by a respiration-dependent primary Na+ pump was not ATP-dependent ion translocations. NaCl stimulated NADH oxidase activity at pH 6.5 but inhibited it at pH 8.5. 2-n-Heptyl-4-hydroxyquinoline N-oxide (HQNO), a respiratory inhibitor that greatly inhibited the primary Na+ pump at pH 6.5 and 8.5, also inhibited the NADH oxidase activity, greatly at pH 6.5 and faintly at pH 8.5. On the other hand, NADH : ubiquinone-1 oxidoreductase activities were stimulated by NaCl to a similar extent at pH 6.5 and 8.5, but in the presence of 0.425 M NaCl it was inhibited by HQNO at pH 8.5 less than at pH 6.5. These results showed that the primary Na+ pump at pH 6.5 is coupled to NADH: quinone oxidoreductase,and suggested that the coupling site of the pump at pH 8.5 was distinct form the site at pH 6.5.

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