Formyl transfer catalyzed by formyl transferase Tetrahydromethanopterin (H 4 MPT) is analogous to tetrahydrofuran (H 4 F) as a methyl- carrier Reversible hydrolysis of N 5,N l0 -methenyl- H 4 MPT to N 5 -formyl-H 4 MPT, is catalyzed by N 5,N 10 -methenyl-H 4 MPT cyclohydrolase