Coupled photooxidation and photoreduction reactions and associated phosphorylation by chromatophores of Rhodosprillum rubrum.

The light-induced flow of electrons in the chlorophyll-containing particles of photosynthetic bacteria can result in a phosphorylation of adenosine diphosphate to form adenosine triphosphate (l-4), a photooxidation of added mammalian cytochrome c and oxidation-reduction dyes (5), or a photoreduction of diphosphopyridine nucleotide (6). The photoreduction of diphosphopyridine nucleotide by chromatophores of Rhdospidlum r&-urn proceeds in the presence of succinate, whereas the photooxidation of mammalian cytochrome c requires the presence of fumarate (5). These data imply a coupled system in which one substance is being reduced while the other is being oxidized. The present investigation concerns a further direct demonstration of the coupled nature of the photooxidation and photoreduction reactions catalyzed by chromatophores of R. rubrum. The most informative system is one in which the reducing equivalents are used to reduce diphosphopyridine nucleotide, while the oxidizing equivalents are transferred to ascorbic acid with the dye 2,6-dichlorophenolindophenol as an intermediate electron carrier. The photophosphorylation which occurs simultaneously has also been followed to obtain some information concerning the connection between these three processes.