Catalyzes the reversible transfer of a formyl group from formylmethanofuran (formyl-MFR) to tetrahydromethanopterin (H(4)MPT) to produce 5-formyl tetrahydromethanopterin (5-formyl-H(4)MPT) and methanofuran (MFR) (By similarity) (PubMed:11054114, PubMed:1483480, PubMed:7601152). Acts via a ternary-complex mechanism. Uses N-furfurylformamide much less efficiently, does not use N-methylformamide or formamide (PubMed:1483480, PubMed:11054114, PubMed:7601152). Protein overexpressed in E.coli has very similar properties to enzyme purified from M.kandleri (PubMed:7601152). 5,6,7,8-tetrahydromethanopterin + H(+) + N-formylmethanofuran = methanofuran + N(5)-formyl-5,6,7,8-tetrahydromethanopterin Requires high salt concentrations for activity and thermostability; 1.5-1.8 M KH(2)PO(4) stimulates activity while stabilizing the enzyme. Optimum pH is 6.5. Optimum temperature is 90 degrees Celsius. One-carbon metabolism; methanogenesis from CO(2); 5,10-methenyl-5,6,7,8-tetrahydromethanopterin from CO(2): step 2/3. Homotetramer composed of two dimers (PubMed:11054114, PubMed:9195883). Dimerization is sufficient for enzyme activity, but tetramerization is required for high thermostability (PubMed:11054114). Belongs to the FTR family.