Uncoupling Agents and Photophosphorylation in Chromatophores and Chloroplasts.

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Abstract
Photophosphorylation in chromatophores from Rhodospirillum rubrum and in spinach chloroplasts was inhibited by 2 agents which are known to uncouple oxidative phosphorylation in mitochondria, namely 2,6-dinitro-4-isooctylphenol (octyl-DNP) and desapidin. In bacterial chromatophores both uncoupling agents inhibited photophosphorylation at comparatively low concentrations. This was the case both in the "physiological system", where no electron carrier had been added to the reaction mixture, and in the "phenazine metho-sulfate -system", after inhibition of the "physiological system" with 2-heptyl-4-hydroxyquinoline-N-oxide (HOQNO) and "by-passing" this inhibition by addition of phenazine methosulfate. In chloroplasts, cyclic photophosphorylation in the presence of added phenazine methosulfate and "pseudocyclic" photophosphorylation in the presence of added flavin mononucleotide (FMN) were inhibited by comparatively low concentrations of octyl-DNP. An uncoupling action by this agent was demonstrated with the non-cyclic system for electron transport from water to ferri-cyanide. Cyclic photophosphorylation in the presence of phenazine methosulfate was inhibited by low concentrations of desapidin. "Pseudo-cyclic" photophosphorylation in the presence of FMN required about a 100 times as high concentrations of desapidin for inhibition as cyclic photophosphorylation. This indicates that desapidin may specifically uncouple only the latter system and that the 2 systems may contain different coupling sites with at least partly different energy transfer reactions.