Roles of Ubiquinone-10 and Rhodoquinone in Photosynthetic Formation of Adenosine Triphosphate by Chromatophores from Rhodospirillum rubrum

Abstract

Abstract 1. The roles of ubiquinone-10 and of rhodoquinone in photosynthetic ATP formation were studied with chromatophores from a blue-green mutant (G-9) of Rhodospirillum rubrum. 2. Chromatophores contained ubiquinone-10 and rhodoquinone in amounts equal approximately to 50% and 10%, respectively, on a molar basis, of that of bacteriochlorophyll. Other quinones were not present in appreciable amounts. 3. Extraction with isooctane of lyophilized chromatophores greatly lowered the activity of photosynthetic ATP formation measured in the presence of either 6.7 x 10-2 m ascorbate (ascorbate-induced) or 4.0 x 10-4 m phenazine methosulfate (PMS-induced). Both phosphorylation activities were reactivated by the addition of either ubiquinone-6 or ubiquinone-10 or the isooctane extract, but not by addition of either phylloquinone or menadione. The addition of appropriate concentrations of rhodoquinone reactivated the PMS-induced, but not the ascorbate-induced, photosynthetic ATP formation. 4. Photosynthetic ATP formation by lyophilized chromatophores and by extracted chromatophores reactivated with ubiquinone-10 was inhibited by antimycin A to the same extent; PMS-induced and ascorbate-induced photosynthetic ATP formation were inhibited approximately 40% and 100%, respectively. Neither type of ATP formation was influenced appreciably by antimycin A, if reactivated by adding rhodoquinone alone. 5. From these findings, it was concluded that ubiquinone-10 is one of the essential components for photosynthetic ATP formation by intact chromatophores.