N5, N10-Methylenetetrahydromethanopterin reductase from Methanosarcina barkeri

N5N10-Methylenetetrahydromethanopterin reductase was purified 13-fold to apparent homogeneity from methanol grown Methanosarcina barkeri. The colourless enzyme was found to be composed of four identical subunits of apparent molecular mass 36 kDa. It catalysed the reduction of methylenetetrahydromethanopterin (Km=15 μM) to methyltetrahydromethanopterin with reduced coenzyme F420 (Km=12 μM) at a specific rate (Vmax) of 2200 μmol min−1· mg protein−1 (Kcat=1320 s−1). With respect to coenzyme specificity, molecular properties and catalytic mechanism the enzyme was found to be similar to CH2=H4MPT reductase of Methanobacterium thermoautotrophicum which phylogenetically is only distantly related to M. barkeri.