Hydrogen‐forming and coenzyme‐F420‐reducing methylene tetrahydromethanopterin dehydrogenase are genetically distinct enzymes in Methanobacterium thermoautotrophicum (Marburg)

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Abstract
A coenzyme‐F420‐reducing and an H2‐forming methylenetetrahydromethanopterin dehydrogenase have been isolated from Methanobacterium thermoautotrophicum (Marburg). Indirect evidence suggested that the former enzyme (32 kDa) might be derived from the latter enzyme (42 kDa) by proteolysis. To test this hypothesis the gene sequence of the H2‐forming dehydrogenase was determined and compared with the N‐terminal amino acid sequence of the F420‐reducing dehydrogenase. No corresponding sequences were found indicating that the two dehydrogenases are genetically distinct enzymes. With purified enzyme preparations it is shown that the activity of the F420‐reducing dehydrogenase is inhibited in the presence of the H2‐forming enzyme. This finding is discussed in terms of substrate competition.

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