Luminescence and respiratory activities of Photobacterium phosphoreum. II. Control by monovalent cations.

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.