Na+-Dependent Activation of NADH Oxidase in Membrane Fractions from Halophilic Vibrio alginolyticus and V. costicolus

Abstract

Membrane-bound NADH oxidase activities from slightly halophilic marine Vibrio alginolyticus and moderately halophilic V. costicolus required 0.3 and 0.5 M Na⁺ respectively, for maximum activity; other cations such as Li⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, were relatively ineffective as replacements for Na⁺. The concentration of Na⁺ required to give half-maximum activity with the NADH oxidase from V. alginolyticus was 82 mM. This value was reduced to 6.4 and 13.8 mM in the presence of 400 mM K⁺ and 10 mM Mg²⁺, respectively, indicating that K⁺ and Mg²⁺ cooperated with Na⁺ for activation. The same pattern of cation dependence was observed with the NADH oxidase from V. costicolus. The NADH oxidase from nonhalophilic Escherichia coli, however, had no specific requirement for Na⁺. Thus, Na⁺-dependent activation of NADH oxidase appeared to be a characteristic feature of these halophilic bacteria. All NADH oxidases examined were influenced by the species of anion present and the order of activating effect followed the lyotropic series: SO₄²⁻ CH₃COO⁻>Cl⁻>NO₃⁻>SCN⁻. Chaotropic anions such as NO³⁻ and SCN⁻ were inhibitory to the NADH oxidases, irrespective of the halophilic nature of the bacterial source.