Axial coordination in nickel porphyrins and nickel-reconstituted heme proteins investigated by Raman-difference and transient-Raman spectroscopy

Nickel porphyrins are of interest because of their occurrence in coal, shale, and petroleum deposits and because of their key role in biological conversion of CO/sub 2/ to methane. The enzyme methylreductase is the enzyme that catalyses the final step, and possibly other steps, in the reduction of CO/sub 2/ to methane. The active site of methylreductase contains a nickel-sirochlorin derivative called F/sub 430/. Understanding the involvement of F/sub 430/ in methane production is of importance to the natural gas industry for utilizing abundant inorganic resources for production of gaseous fuels. Recently, we have used resonance Raman spectroscopy to investigate axial ligand processes at the metal in Ni-porphyrin complexes and Ni-reconstituted heme proteins. These studies provide useful models for axial ligation and for Ni-porphyrin-protein interactions that may be important in the function of the methylreductase enzyme. 8 refs.