Oxidative phosphorylation in extracts of Rhodospirillum rubrum.

The purple photosynthetic bacterium, Rhodospirillum rubrum, grows anaerobically only when illuminated with light of appropriate wave lengths. Extracts prepared from cells grown in this manner catalyze an anaerobic light-dependent phosphorylation of adenosine diphosphate to adenosine triphosphate (1). However, R. rubrum also can be grown heterotrophically in darkness if oxygen is provided (2). Under these conditions, synthesis of the photosynthetic pigments, bacteriochlorophyll and carotenoids, is suppressed (2, 3)) and the organisms presumably derive energy for growth by oxidative phosphorylation. These dark-grown cells of R. rubrum are capable of a rapid synthesis of the photosynthetic pigments under certain conditions, e.g. illumination in the absence of oxygen, or exposure to low oxygen tension in darkness (3, 4). During the course of experiments designed to detect precursors of the photoactive pigment system, it was observed that extracts of dark-grown cells catalyzed oxidative phosphorylation. This report describes the general properties of the oxidative phosphorylation catalyzed by extracts of cells grown either aerobically in darkness or anaerobically in light. The results indicate that oxidative phosphorylation and photophosphorylation are catalyzed by two apparently independent systems, differing markedly in sensitivity to certain inhibitors and in composition.