| Abstract
| - In Gram-positive bacteria and other prokaryotes containing succinate:menaquinone reductases,it has previously been shown that the succinate oxidase and succinate:menaquinone reductase activitiesare lost when the transmembrane electrochemical proton potential, Δp, is abolished by the rupture of thebacteria or by the addition of a protonophore. It has been proposed that the endergonic reduction ofmenaquinone by succinate is driven by the electrochemical proton potential. Opposite sides of thecytoplasmic membrane were envisaged to be separately involved in the binding of protons upon thereduction of menaquinone and their release upon succinate oxidation, with the two reactions linked bythe transfer of two electrons through the enzyme. However, it has previously been argued that the observedΔp dependence is not associated specifically with the succinate:menaquinone reductase. Definitive insightinto the mechanism of catalysis of this reaction requires a corresponding functional characterization of anisolated, membrane-bound succinate:menaquinone reductase from a Gram-positive bacterium. Here, wedescribe the purification, reconstitution into proteoliposomes, and functional characterization of the diheme-containing succinate:menaquinone reductase from the Gram-positive bacterium Bacillus licheniformis and,with the help of the design, synthesis, and characterization of quinones with finely tuned oxidation/reduction potentials, provide unequivocal evidence for Δp-dependent catalysis of succinate oxidation byquinone as well as for Δp generation upon catalysis of fumarate reduction by quinol.
|
