Energy Conservation by the H2:Heterodisulfide Oxidoreductase fromMethanosarcina mazeiGö1: Identification of Two Proton-Translocating Segments

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Abstract
The membrane-bound H2:heterodisulfide oxidoreductase system of the methanogenic archaeonMethanosarcina mazeiGö1 catalyzed the H2-dependent reduction of 2-hydroxyphenazine and the dihydro-2-hydroxyphenazine-dependent reduction of the heterodisulfide of HS-CoM and HS-CoB (CoM-S-S-CoB). Washed inverted vesicles of this organism were found to couple both processes with the transfer of protons across the cytoplasmic membrane. The maximal H+/2e−ratio was 0.9 for each reaction. The electrochemical proton gradient (ΔμH+) thereby generated was shown to drive ATP synthesis from ADP plus Pi, exhibiting stoichiometries of 0.25 ATP synthesized per two electrons transported for both partial reactions. ATP synthesis and the generation of ΔμH+were abolished by the uncoupler 3,5-di-tert-butyl-4-hydroxybenzylidenemalononitrile (SF 6847). The ATP synthase inhibitorN,N′-dicyclohexylcarbodiimide did not affect H+translocation but led to an almost complete inhibition of ATP synthesis and decreased the electron transport rates. The latter effect was relieved by the addition of SF 6847. Thus, the energy-conserving systems showed a stringent coupling which resembles the phenomenon of respiratory control. The results indicate that two different proton-translocating segments are present in the H2:heterodisulfide oxidoreductase system; the first involves the 2-hydroxyphenazine-dependent hydrogenase, and the second involves the heterodisulfide reductase.