H2-forming N5,N10-methylenetetrahydromethanopterin dehydrogenase from Methanobacterium thermoautotrophicum. Studies of the catalytic mechanism of H2 formation using hydrogen isotopes.
H2-forming N5,N10-methylenetetrahydromethanopterin dehydrogenase is a novel hydrogenase found in most methanogenic archaea. It catalyzes the reversible conversion of N5,N10-methylenetetrahydromethanopterin (CH2 = H4MPT) to N5,N10-methenyltetrahydromethanopterin (CH identical to H4MPT+) and dihydrogen; CH2 = H4MPT + H+<-->CH identical to H4MPT(+) + H2; delta G degrees ' = + 5 kJ/mol. In the following investigation, the formation of H2, HD and D2 was studied in experiments in which either the methylene group of CH2 = H4MPT or water were deuterium labelled. In the case of CD2 = H4MPT and H2O, the dihydrogen formed immediately after the start of the reaction was composed of approximately 50% HD and 50% of H2 at all pH tested. In the case of CH2 = H4MPT and D2O, the dihydrogen generated was composed of approximately 50% HD and 50% D2 at pD 5.7 and of approximately 85% HD and 15% D2 at pD 7.0. Evidence is presented that the enzyme catalyzes a CH identical to H4MPT(+)-dependent isotopic exchange between HD and H2O and between HD and D2O, yielding H2 and D2, respectively. A catalytic mechanism aimed to explain these findings is discussed.
Laboratorium für Mikrobiologie des Fachbereichs Biologie, Philipps-Universität Marburg, Federal Republic of Germany.
B
B
Schwörer
V M
VM
Fernandez
C
C
Zirngibl
R K
RK
Thauer
D003903:Deuterium / Q000378:metabolism; D017666:Deuterium Oxide; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D017014:Methanobacterium / Q000201:enzymology*; D000587:Oxidoreductases Acting on CH-NH Group Donors / Q000494:pharmacology*; D014867:Water / Q000378:metabolism
D014867:Water; D006859:Hydrogen; D003903:Deuterium; D000587:Oxidoreductases Acting on CH-NH Group Donors; C047126:methylenetetrahydromethanopterin dehydrogenase; D017666:Deuterium Oxide