title: The effect of o-phenanthroline on the midpoint potential of the primary electron acceptor of photosystem II.
abstract: The primary electron acceptor of Photosystem II has a midpoint oxidation-reduction potential of +95 mV at pH 7.0 in Photosystem II chloroplast fragments prepared by digitonin treatment. The midpoint potential of the acceptor has a pH dependence of -60 mV/pH unit. At concentrations that inhibit oxygen evolution, o-phenanthroline shifts the midpoint potential of the primary acceptor by +70 mV. The shifted potential retains the same dependence on pH. The effect of o-phenanthroline suggests that it interacts directly with the primary electron acceptor of photosystem II in a manner similar to that reported previously for the primary electron acceptor in purple photosynthetic bacteria.
mesh_terms: D002736:Chloroplasts / Q000187:drug effects / Q000378:metabolism*; D004072:Digitonin; D004579:Electron Transport; D006863:Hydrogen-Ion Concentration; D010618:Phenanthrolines / Q000494:pharmacology*; D010785:Photophosphorylation / Q000187:drug effects*; D010944:Plants; D011199:Potentiometry
chemical_list: D010618:Phenanthrolines; D004072:Digitonin