Methyl‐coenzyme‐M reductase from Methanobacterium thermoautotrophicum (strain Marburg)

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Abstract
Methyl‐coenzyme‐M reductase from Methanobacterium thermoautotrophicum (strain Marburg) was purified to a stage where, besides the α, β and γ subunits, no additional polypeptides were detectable in the preparation. Under appropriate conditions the enzyme was found to catalyze the reduction of methyl‐CoM with 7‐mercaptoheptanoylthreonine phosphate (H‐S‐HTP) to CH4 at a specific rate of 2.5 μmol · min−1· mg protein−1. This finding contradicts a recent report that methyl‐CoM reductase is only active when some contaminating proteins are present.The two polypeptides encoded by the open reading frames ORF1 and ORF2 of the methyl‐CoM reductase transcription unit did not co‐purify with the α, β and γ subunits. They were neither required nor did they stimulate the activity under the assay conditions.3‐Bromopropanesulfonate (apparent Ki= 0.05 μM) and 2‐azidoethanesulfonate (apparent Ki= 1 μM) were found to be two new competitive inhibitors of methyl‐CoM reductase. Both inhibitors were considerably more effective than the “classical” 2‐bromoethanesulfonate (apparent Ki= 4 μM).

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