Methanofuran

Methanofurans are a family of chemical compounds found in methanogenic archaea. These species feature a 2-aminomethylfuran linked to phenoxy group. At least three different end groups are recognized: R = tricarboxyheptanoyl (methanofuran), glutamyl-glutamyl (methanofuran b), tricarboxy-2-hydroxyheptanoyl (methanofuran c, see picture).
Formylation of MFR.
Methanofuran converts to formylmethanofuran in an early stage of methanogenesis. 
The enzyme formylmethanofuran dehydrogenase (EC: 1.2.99.5) formylates methanofuran using , the primary C1 source in methanogenesis.
Deformylation of MFR.
The enzyme formylmethanofuran:tetrahydromethanopterin formyltransferase catalyzes the transfer of the formyl group from formylmethanofuran to N5 on tetrahydromethanopterin, . This enzyme has been crystallized; it contains no prosthetic group.