Recent biochemical and metagenomic data indicate that not yet cultured archaea closely related to methanogenic archaea of the order of Methanosarcinales are involved in the anaerobic oxidation of methane (AOM) with sulfate in marine sediments. The DNA from the methanotrophic archaea has been shown to harbor gene homologues for methyl-coenzyme M reductase (MCR), which in methanogenic archaea mediates the methane forming reaction. In microbial mats catalyzing AOM the nickel enzyme has been shown to be present in concentrations of 10% of the extracted proteins. Based on these and other findings it has been proposed that AOM with sulfate proceeds at least in part via reversed methanogenesis.
Until now, only the catalytic properties of MCR from methanogenic archaea are known. Those of the enzyme from methanotrophic archaea can, however, be estimated from these properties and the thermodynamics of the MCR catalyzed reaction. They appear consistent with the involvement of MCR in AOM with sulfate mediated by methanotrophic archaea.
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