Novel reactions involved in energy conservation by methanogenic archaea

Methanogenic archaea of the order Methanosarcinales which utilize C-1 compo unds such as methanol, methylamines or H-2+CO2, employ two novel membrane-b ound electron transport systems generating an electrochemical proton gradie nt: the H-2:heterodisulfide oxidoreductase and the F420H2 :heterodisulfide oxidoreductase, The systems are composed of the heterodisulfide reductase a nd either a membrane-bound hydrogenase or a F420H2 dehydrogenase which is f unctionally homologous to the proton-translocating NADH dehydrogenase, Cyto chromes and the novel electron carrier methanophenazine are also involved. In addition, the methyl-H4MPT:HS-CoM methyltransferase is bioenergetically relevant. The enzyme couples methyl group transfer with the translocation o f sodium ions and seems to be present in all methanogens, The proton-transl ocating systems with the participation of cytochromes and methanophenazine have been found so far only in the Methanosarcinales, (C) 1999 Federation o f European Biochemical Societies.