Luminescence and Respiratory Activities of Photobacterium phosphoreum

II. Control by Monovalent Cations

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Luminescent activity of spheroplasts of the cells of Photobacterium phosphoreum was stimulated by Rb⁺ and K⁺ and inhibited by Na⁺ in the medium. Opposite effects of these ions were observed on the rate of O₂ consumption of the spheroplasts through the cytochrome and luciferase electron transfer systems. In vitro activities of NADH-FMN reductase and luciferase were only slightly stimulated by Rb⁺, K⁺, and Na⁺, while Na⁺ exhibited significant activation of the NADH-oxidizing activity of the cells. The redox level of cytochrome b in the spheroplasts during steady-state respiration in an Na⁺ medium was more reduced, while that of NAD(P) was more oxidized, than those in an Rb⁺ or K⁺ medium. Na⁺ activates the cytochrome electron transfer system at a point between NADH and cytochrome b, and thus has a stimulative effect on cellular O₂ consumption. Rb⁺ and K⁺ do not show similar activation, but the cellular NAD(P) was brought to a more reduced level, so that in vivo luminescence is stimulated in an Rb⁺ or K⁺ medium.