H2-forming N5,N10-methylenetetrahydromethanopterin dehydrogenase: mechanism of H2 formation analyzed using hydrogen isotopes.

H2-forming N5,N10-methylenetetrahydromethanopterin dehydrogenase catalyzes the reversible dehydrogenation of N5,N10-methylenetetrahydromethanopterin (CH2 = H4MPT) to N5,N10-methenyltetrahydromethanopterin (CH = H4MPT+) and H2. In D2O both HD and D2 are formed from CH2 = H4MPT and in H2O both HD and H2 from CD2 = H4MPT. Evidence is presented that HD is not an intermediate in the formation of D2 and H2, respectively.