Activation and reaction kinetics of the dimethylamine coenzyme M methyltransfer in Methanosarcina barkeri strain Fusaro

Dimethylamine/5-hydroxybenzimidazolylcobamide methyltransferase (DMA-MT) fr om Methanosarcina barkeri Fusaro catalyzes (V-max = 4700 nmol.min(-1).mg(-1 ) protein; k(cat) = 7.8 s(-1)) the transfer of a methyl group from dimethyl amine (apparent K-m = 0.45 mM) to its corrinoid prosthetic group to yield m onomethylamine (MMA) and the methylated enzyme. The product, MMA? is a comp etitive inhibitor of the reaction (apparent K-i = 5.5 mM). The methyl group bound to the corrinoid prosthetic group of DMA-MT is subsequently transfer red to coenzyme M in a reaction mediated by methylcobalamin/coenzyme M meth yltransferase isoenzyme II [MT2(II)], which binds with high affinity to DMA -MT (apparent K-m = 0.22 mu M). As isolated, DMA-MT is inactive, but it can enzymically be reactivated by methyltransferase activating protein (MAP), ATP, and hydrogenase. Apart from the established role in corrinoid activati on, ATP was found to act as a powerful allosteric effector on the methyltra nsferase reaction. The results of kinetic studies, supported by the resolut ion of as-yet partially purified auxiliary protein fractions, demonstrate t hat DMA-MT, MT2(II), MAP, and hydrogenase are the only enzymic components i nvolved in the dimethylamineicoenzyme M methyltransfer in M. barkeri Fusaro .