| Summary: | Some evidence for the participation of methyl quinones in oxidative phosphorylation is presented and discussed. Although methyl quinones seem to be definitely involved in electron transport in particulate systems, there is no unequivocal evidence that they are actually involved in the coupling reaction. Several hypothetical schemes for oxidative phosphorylation are discussed with particular emphasis on those involving hydro-quinone phosphates. The Vilkas -Lederer scheme and the more recent mechanism proposed by Erickson, Wagner, and Folkers are discussed in detail. An in vitro investigation of the latter proposal is the subject of the present work. Hydrogen isotope exchange in methyl quinones was observed in the presence of carbonate or triethylamine using the techniques of infra-red spectroscopy, NMR spectroscopy, mass spectrometry and scintillation spectrometry. The exchange reactions of duroquinone and 2, 3-dimethyl-J, 4-naphthoquinone together with their derivatives were investigated over a range of pH and at different temperatures. The large primary isotope effect for the reaction indicates that removal of a proton from the methyl group of the quinone is the rate determining step in those reactions 3. involving a quinone methide intermediate and offers an explanation for the negative results of the in vivo hydrogen isotope experiments. The reaction of phosphoric acid and its various anions with both stable and transient quinone methides was investigated. There was no evidence for any nucleophilic addition of a phosphate to a quinone methide, polymerisation of the latter being the only reaction observed. A synthesis of p-hydroxybenzyl phosphate and a study of its behaviour under oxidising conditions were attempted. Production of p-hydroxybenzyl phosphate in situ under acidic or basic conditions resulted in its immediate decomposition to inorganic phosphate and the quinone methide, precluding any observation of oxidative phosphorylation. No evidence for oxidative acylation with the isolable 2, 6-di-t-butyl-4-hydroxybenzyl acetate was obtained.
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