2 F-420-REDUCING HYDROGENASES IN METHANOSARCINA-BARKERI

F-420-reducing hydrogenases are nickel iron-sulfur flavoproteins invol ved in CO2 reduction with H-2 to methane in methanogenic archaea. Evid ence is presented that Methanosarcina barkeri contains two isoenzymes for which the encoding genes have been cloned and sequenced. The genes are organized in two operons, frhADGB and freAEGB, each comprising fo ur open reading frames. Transcription analysis revealed that both oper ons are transcribed during growth of Ms. barkeri on H-2/CO2, on methan ol, and on trimethylamine, but not during growth on acetate.