Myoglobin Reconstituted with Ni Tetradehydrocorrin as a Methane-Generating Model of Methyl-coenzyme M Reductase

Myoglobin reconstituted with Ni tetradehydrocorrin was investigated as a model of F430-containing methyl-coenzyme M reductase, which catalyzes anaerobic methane generation. The Ni^II tetradehydrocorrin complex has a Ni^II /Ni^I redox potential of -0.34 V vs. SHE and EPR spectroscopy indicates the formation of a Ni^I species upon reduction by dithionite. This redox potential is approximately 0.31 V more positive than that of F430. The Ni^I tetradehydrocorrin moiety is bound to the apo-form of myoglobin to yield the reconstituted protein. Methane gas is generated in the reaction of the model with methyl iodide in the presence of the reconstituted protein under reductive conditions, whereas the Ni^I complex itself does not produce methane gas. This is the first example of a protein-based functional model of F430-containing methyl-coenzyme M reductase.