Abstract

The aerobic respiratory chain of Vibrio alginolyticus possesses two different kinds of NADH oxidase systems, i.e., an Na^+ -dependent NADH oxidase system and an Na^+ -independent NADH oxidase system. When deamino-NADH, which is the only substrate for the Na^+ -dependent NADH oxidase system, was used as a substrate, the maximum activities of Na^+ -dependent NADH:quinone oxidoreductase and Na^+ -dependent NADH oxidase were obtained at about 0.06 M and 0.2 M NaCl, respectively. When NADH, which is a substrate for both Na^+ -dependent and Na^+ -independent NADH oxidase systems was used as a substrate, the NADH oxidase activity had a pH optimum at about 8.0. In contrast, when deamino-NADH was used as a substrate, the NADH oxidase activity had a pH optimum at about 9.0. On the other hand, inside-out membrane vesicles prepared from the wild-type bacterium generated only a very small [delta]pH by the NADH oxidase system, whereas inside-out membrane vesicles prepared from Nap1, which is a mutant defective in the Na^+ pump, generated [delta]pH to a considerable extent by the NADH oxidase system. On the basis of the results, it was concluded that the respiratory chain-linked components of V. alginolyticus affect each other.

• Keywords: marine bacterium; Vibrio alginolyticus; respiratory chain; Na^+ -dependent NADH oxidase; Na^+ -indep