5,10-methylene-5,6,7,8-tetrahydromethanopterin 5,10-methylene-H4MPT 5,10-methylene-tetrahydromethanopterin METHYLENETETRAHYDROMETHANOPTERIN N5,N10-methylene-5,6,7,8-tetrahydromethanopterin N5,N10-methylenetetrahydromethanopterin methylene-H4MPT