title: Photosystem II energy coupling in chloroplasts with H2O2 as electron donor.
abstract: NH2OH-treated, non-water-splitting chloroplasts can oxidize H2O2 to O2 through Photosystem II at substantial rates (100--250 muequiv . h-1 . mg-1 chlorophyll with 5 mM H2O2) using 2,5-dimethyl-p-benzoquinone as an electron acceptor in the presence of the plastoquinone antagonist dibromothymoquinone. This H2O2 leads to Photosystem II leads to dimethylquinone reaction supports phosphorylation with a P/e2 ratio of 0.25--0.35 and proton uptake with H+/e values of 0.67 (pH 8)--0.85 (pH 6). These are close to the P/e2 value of 0.3--0.38 and the H+/e values of 0.7--0.93 found in parallel experiments for the H2O leads to Photosystem II leads to dimethylquinone reaction in untreated chloroplasts. Semi-quantitative data are also presented which show that the donor leads to Photosystem II leads to dibromothymoquinone (leads to O2) reaction can support phosphorylation when the donor used is a proton-releasing reductant (benzidine, catechol) but not when it is a non-proton carrier (I-, ferrocyanide).
mesh_terms: D002736:Chloroplasts / Q000187:drug effects / Q000378:metabolism*; D003991:Dibromothymoquinone / Q000494:pharmacology; D004579:Electron Transport; D006861:Hydrogen Peroxide / Q000378:metabolism*; D006898:Hydroxylamines / Q000494:pharmacology; D007700:Kinetics; D010084:Oxidation-Reduction; D010785:Photophosphorylation / Q000187:drug effects; D010788:Photosynthesis / Q000187:drug effects; D010944:Plants
chemical_list: D006898:Hydroxylamines; D003991:Dibromothymoquinone; D006861:Hydrogen Peroxide