Methane monooxygenase catalytic cycle

Basch, H., Musaev, D.G., Mogi, K. and Morokuma, K. (2001b) A density ftinctunal study of the completion of the methane monooxygenase catalytic cycle. Methanol complex to MMOH resing state, J. Phys. Chem. B 105, 8452-8460. 

Lee, S.-K., Nesheim, J. C., and Lipscomb, J. D., 1993a, Transient intermediates of the methane monooxygenase catalytic cycle, J. Biol. Chem. 268 21569n21577. 

Bollinger, J. M., Krehs, C., Vicol, A., Chen, S. X., Ley, B. A., Edmondson, D. E., and Huynh, B. H., 1998, Engineering the diiron site of Escherichia coli ribonucleotide reductase protein R2 to accumulate an intermediate similar to H-peroxo, the putative peroxodiiron(III) complex from the methane monooxygenase catalytic cycle. J. Am. Chem. Soc. 120 1094nl095. 

Wallar, B. J. Lipscomb, J. D. Methane monooxygenase component B mutants alter the kinetics of steps throughout the catalytic cycle. Biochemistry 2001, 40(7), 2220-2233. 

Shteinman, A. A., 1995, The mechanism of methane and dioxygen activation in the catalytic cycle of methane monooxygenase, FEES Lett. 362 5n9. 

The peroxo species has only been observed in the E. coli R2 mutant D84E (Bollinger et al., 1998), but is a well-known intermediate in the analogous catalytic cycle of methane monooxygenase (Liu et al., 1995). The peroxo species in D84E is a precursor of the tyrosyl radical-diiron centre, however it was not possible to determine whether the RTF mutant stabilised the intermediate enough to be observed, or if the mutation caused a new intermediate to follow a reaction sequence more similar to that of methane monooxygenase. 

Methane is oxidized under aerobic conditions by a group of bacteria called methanotrophs. These widespread bacteria play an important role in the global cycling of methane. Two types of methane oxidation systems are known, a ubiquitous particulate methane monooxygenase (pMMO) and a cytoplasmic soluble methane monooxygenase (sMMO) found in only a few strains. These enzymes have different catalytic characteristics, and so it is important to know the conditions under which each is expressed. In those strains containing both sMMO and pMMO, the available copper concentration controls which enzyme is expressed. However, the activity of the pMMO is also affected by copper. Data on methane oxidation in natural samples suggest that methanotrophs are not copper-limited in nature and express the pMMO predominantly. 

Xue, G. Fiedler, A. T. Martinho, M. Mfinck, E. Que, L. Jr. Insights into P-to-Q conversion in the catalytic cycle of methane monooxygenase from a synthetic model point of view. Proc. Natl. Acad. Sci. USA 2008, 105, 20615-20620. 

B. G. Fox, Mechanistic Studies of the Catalytic Cycle of Methane Monooxygenase from Methylosinus trichosporium OB3b, Ph.D. Thesis, University of Minnesota (1989). 

Scheme XI.6. The catalytic cycle proposed for alkane oxidation by Oi promoted by the binuclear methane monooxygenase center.

Biomimetic studies are currently focused on generating diiron complexes that can serve as structural and/or electronic models for oxidation states higher than Fe " that are proposed to partake in the catalytic cycles of diiron proteins such as methane monooxygenase and ribonucleotide reductase. Mossbauer spectroscopy has played a leading role in the eharacterization... 

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