Novel reactions involved in energy conservation by methanogenic archaea

Abstract

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 420H 2:heterodisulfide oxidoreductase. The systems are composed of the heterodisulfide reductase and either a membrane-bound hydrogenase or a F 420H 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 4MPT: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.