Formation of a Nickel−Methyl Species in Methyl-Coenzyme M Reductase, an Enzyme Catalyzing Methane Formation

An organometallic methyl−nickel species was detected in the enzyme methyl-coenzyme M reductase (MCR). This is the key enzyme in microbial methane production and is probably also involved in anaerobic methane oxidation. Incubation of MCR with ¹³C-bromomethane results in the formation of an electron paramagnetic resonance (EPR) active nickel−methyl species in the active site of this enzyme. High-resolution pulse electron nuclear double resonance and hyperfine sublevel correlation investigations showed the presence of ¹³C hyperfine couplings of 18−44 MHz that are associated with the nickel-based EPR signal. The large ¹³C hyperfine interaction shows unambiguously that the methyl group from bromomethane is directly coordinated to the nickel ion. The EPR structure and parameters are fully supported by density functional theory calculations.