THE FORMYLMETHANOFURAN DEHYDROGENASE ISOENZYMES IN METHANOBACTERIUM-WOLFEI AND METHANOBACTERIUM-THERMOAUTOTROPHICUM - INDUCTION OF THE MOLYBDENUM ISOENZYME BY MOLYBDATE AND CONSTITUTIVE SYNTHESIS OF THE TUNGSTEN ISOENZYME

Formylmethanofuran dehydrogenase catalyzes the first step in methane f ormation from CO2 in methanogenic archaea. Methanobacterium wolfei and Methanobacterium thermoautotrophicum have been shown to contain two i soenzymes, a tungsten-containing isoenzyme (Fwd) and a molybdenum-cont aining isoenzyme (Fmd). We report here that in both thermophilic organ isms the encoding genes are organized in a highly conserved fwdHFGDACB tungsten operon and in an fmdECB molybdenum operon. In both organisms , the tungsten isoenzyme was found to be constitutively transcribed, w hereas the transcription of the molybdenum operon was induced by molyb date. Induction by molybdate was not significantly affected by tungsta te.