Methanogenic archaea of the order Methanosarcinales which utilize C(1) compounds such as methanol, methylamines or H(2)+CO(2), employ two novel membrane-bound electron transport systems generating an electrochemical proton gradient: the H(2):heterodisulfide oxidoreductase and the F(420)H(2):heterodisulfide oxidoreductase. The systems are composed of the heterodisulfide reductase and either a membrane-bound hydrogenase or a F(420)H(2) dehydrogenase which is functionally homologous to the proton-translocating NADH dehydrogenase. Cytochromes and the novel electron carrier methanophenazine are also involved. In addition, the methyl-H(4)MPT:HS-CoM methyltransferase is bioenergetically relevant. The enzyme couples methyl group transfer with the translocation of sodium ions and seems to be present in all methanogens. The proton-translocating systems with the participation of cytochromes and methanophenazine have been found so far only in the Methanosarcinales.