Abstract
Cyclic photophosphorylation catalyzed by chromatophores derived from the facultative phototroph, Rhodopseudomonas capsulata was investigated. In the absence of an external electron donor such as succinate, cyclic photophosphorylation is strongly inhibited by O2. Maximal phosphorylation rates are obtained in the presence of molecular hydrogen. Cytochrome c and bovine serum albumin have no significant effects on the reaction. However, dichlorophenolindophenol and phenazonium methosulfate are inhibitory to cyclic photophosphorylation. Cyclic photophosphorylation is sensitive to antimycin A, but highly resistant to heptylhydroxy-quinoline-N-oxide. Neither phenazonium methosulfate, nor dichlorophenolindophenol or tetramethyl-p-phenylenediamine can effect antimycin-insensitive cyclic photophosphorylation. Oligomycin strongly inhibits the phosphorylation. Overreduction caused by the ascorbate-dichlorophenolindophenol couple results in strong inhibition of phosphorylation. Addition of fumarate decreases the inhibition caused by overreduction. However, the fumarate mediated phosphorylation is nearly completely inhibited by antimycin A. Atebrine is a strong inhibitor for cyclic photophosphorylation, whereas dinitrophenol is only a weak inhibitor.
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