title: The mechanism of quinonediimine acceptor activity in photosynthetic electron transport.
abstract: The rates of electron flow catalyzed by a variety of unsubstituted and C- or N-methylated quinonediimine electron acceptors in a reaction requiring photosystem II in KCN-inhibited chloroplasts vary according to the structure of acceptor used. Quinonediimine, but not quinone, electron acceptor activities are inhibited by a variety of uncouplers. Kinetic analysis of this inhibition shows that it is competitive. Low concentrations of aniline also inhibit the activity of C-methylated quinonediimines, but this appears to be due to a chemical reaction between the acceptor and aniline at low pH inside the chloroplast. Light-induced uptake of a quinonediimine, p-phenylenediimine, was shown to occur in a DCMU-sensitive reaction. Methylamine uncoupling inhibits this uptake to the same extent as it inhibits electron flow. Experiments with a lipophobic acceptor, N,N,N',N'-tetramethyl-p-phenylenediimine, indicate that it catalyzes electron flow by the same mechanism as other quinonediimines. A model is proposed to account for quinonediimine-catalyzed electron flow.
mesh_terms: D001692:Biological Transport; D002736:Chloroplasts / Q000187:drug effects / Q000378:metabolism*; D003486:Cyanides / Q000494:pharmacology; D004237:Diuron / Q000494:pharmacology; D007097:Imines / Q000494:pharmacology*; D007700:Kinetics; D008027:Light; D008744:Methylamines / Q000494:pharmacology; D010655:Phenylenediamines / Q000378:metabolism; D010788:Photosynthesis / Q000187:drug effects*; D010944:Plants; D011809:Quinones / Q000494:pharmacology*
chemical_list: D003486:Cyanides; D007097:Imines; D008744:Methylamines; D010655:Phenylenediamines; D011809:Quinones; D004237:Diuron