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  • Title: The mechanism of quinonediimine acceptor activity in photosynthetic electron transport.
    Author: Guikema JA, Yocum CF.
    Journal: Biochemistry; 1976 Jan 27; 15(2):362-7. PubMed ID: 1247521.
    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.
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