Deconstructing F(430): quantum chemical perspectives of biological methanogenesis.
What stabilizes the unique Ni(I) state of the active form of coenzyme F(430) and of methylcoenzyme M reductase, the enzyme responsible for the last methane-evolving step of biological methanogenesis? A survey of F(430) model compounds suggests that the monoanionic nature of the F(430) ligand goes a long way toward explaining the stability of Ni(I) F(430). Second, nature appears to have manipulated the stereochemistry of the macrocycle, particularly that of the 12- and 13- substituents, so that the cofactor is sterically constrained against ruffling and forced to adopt a relatively planar conformation with long Ni--N distances. Third, the carbonyl substituent at the 15-meso position electronically stabilizes the Ni(I) state of the cofactor. With regard to the mechanism of methylcoenzyme M reductase, the most reasonable mechanism, in our opinion, involves a Ni(I)-mediated homolytic cleavage of the S--CH(3) bond in methylcoenzyme M, followed immediately by the quenching of the methyl radical by coenzyme B (a thiol) to produce methane.
Ghosh
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Institute of Chemistry, University of Tromsø, N-9037, Tromsø, Norway. abhik@chem.uit.no
Wondimagegn
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Ryeng
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D008665:Metalloporphyrins / Q000737:chemistry* / Q000378:metabolism; D008697:Methane / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D009532:Nickel / Q000737:chemistry / Q000378:metabolism; D010088:Oxidoreductases / Q000737:chemistry / Q000378:metabolism; D011789:Quantum Theory
D008665:Metalloporphyrins; C023540:factor F430; D009532:Nickel; D010088:Oxidoreductases; C021572:methyl coenzyme M reductase; D008697:Methane