Hydrogen Isotope Effects in the Reactions Catalyzed by H2-forming N5,N10-Methylenetetrahydromethanopterin Dehydrogenase from Methanogenic Archaea
| Autor: | Rudolf K. Thauer, Gudrun C. Hartmann, Andreas R. Klein |
|---|---|
| Rok vydání: | 1995 |
| Předmět: |
Oxidoreductases Acting on CH-NH Group Donors
Hydrogenase Hydrogen Methanococcus Methanobacterium Inorganic chemistry chemistry.chemical_element Dehydrogenase Euryarchaeota Hydrogen-Ion Concentration Deuterium Biochemistry Pterins Kinetics chemistry.chemical_compound chemistry Kinetic isotope effect Dehydrogenation Methylenetetrahydromethanopterin dehydrogenase Protons Methylene |
| Zdroj: | European Journal of Biochemistry. 233:372-376 |
| ISSN: | 1432-1033 0014-2956 |
| DOI: | 10.1111/j.1432-1033.1995.372_1.x |
| Popis: | H2-forming N5,N10-methylenetetrahydromethanopterin dehydrogenase from methanogenic Archaea, which is a novel hydrogenase containing neither nickel nor iron-sulfur clusters, catalyzes the reversible reduction of N5,N10-methenyltetrahydomethanopterin (CH identical to H4MPT+) with H2 to N5,N10-methylenetetrahydromethanopterin (CH2 = H4MPT) and a proton (delta G degree' = -5.5 kJ/mol). The enzyme also catalyzes a CH identical to H4MPT(+)-dependent H2/H+ exchange. We report here on kinetic deuterium isotope effects in these reactions. When CH identical to H4MPT+ reduction was performed with D2 instead of H2, Vmax and the Km did not change. A primary isotope effect of 1 was found at all pH and temperatures tested and independent of whether H2O or D2O was the solvent. The findings indicate that a step other than the activation of H2 was rate-determining in CH identical to H4MPT+ reduction with H2. This was substantiated by the observation that also the CH identical to H4MPT(+)-dependent H2/H+ exchange reaction did not exhibit an appreciable deuterium isotope effect. Vmax for CH2 = H4MPT dehydrogenation to CH identical to H4MPT+ and H2 was only 2-3 times higher than for CD2 = H4MPT dehydrogenation to CD identical to H4MPT+ and HD. Such a small primary isotope effect indicates that the breakage of the C-H bond in the methylene group of CH2 = H4MPT was only rate-limiting when hydrogen was substituted by a deuterium. |
| Databáze: | OpenAIRE |
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