Abstract
1. The roles of the three protein components of soluble methane mono-oxygenase were investigated by the use of rapid-reaction techniques. The transfer of electrons through the enzyme complex from NADH to methane/O2 was also investigated. 2. Electron transfer from protein C, the reductase component, to protein A, the hydroxylase component, was demonstrated. Protein C was shown to undergo a three-electron--one-electron catalytic cycle. The interaction of protein C with NADH was investigated. Reduction of protein C was shown to be rapid, and a charge-transfer interaction between reduced FAD and NAD+ was observed; this intermediate was also found in static titration experiments. Thus the binding of NADH, the reduction of protein C and the intramolecular transfer of electrons through protein C were shown to be much more rapid than the turnover rate of methane mono-oxygenase. 3. The rate of transfer of electrons from protein C to protein A was shown to be lower than the reduction of protein C but higher than the turnover rate of methane mono-oxygenase. Association of the proteins was not rate-limiting. The amount of protein A present in the system had a small effect on the rate of reduction of protein C, indicating some co-operativity between the two proteins. 4. Protein B was shown to prevent electron transfer between protein C and protein A in the absence of methane. On addition of saturating concentrations of methane electron transfer was restored. With saturating concentrations of methane and O2 the observed rate constant for the conversion of methane into methanol was 0.26 s-1 at 18 degrees C. 5. By the use of [2H4]methane it was demonstrated that C-H-bond breakage is likely to be the rate-limiting step in the conversion of methane into methanol.
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- Axcell B. C., Geary P. J. Purification and some properties of a soluble benzene-oxidizing system from a strain of Pseudomonas. Biochem J. 1975 Jan;146(1):173–183. doi: 10.1042/bj1460173. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Colby J., Dalton H. Characterization of the second prosthetic group of the flavoenzyme NADH-acceptor reductase (component C) of the methane mono-oxygenase from Methylococcus capsulatus (Bath). Biochem J. 1979 Mar 1;177(3):903–908. doi: 10.1042/bj1770903. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Colby J., Dalton H. Resolution of the methane mono-oxygenase of Methylococcus capsulatus (Bath) into three components. Purification and properties of component C, a flavoprotein. Biochem J. 1978 May 1;171(2):461–468. doi: 10.1042/bj1710461. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Green J., Dalton H. Protein B of soluble methane monooxygenase from Methylococcus capsulatus (Bath). A novel regulatory protein of enzyme activity. J Biol Chem. 1985 Dec 15;260(29):15795–15801. [PubMed] [Google Scholar]
- Green J., Dalton H. Steady-state kinetic analysis of soluble methane mono-oxygenase from Methylococcus capsulatus (Bath). Biochem J. 1986 May 15;236(1):155–162. doi: 10.1042/bj2360155. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Lambeth J. D., Kamin H. Adrenodoxin reductase and adrenodoxin. Mechanisms of reduction of ferricyanide and cytochrome c. J Biol Chem. 1977 May 10;252(9):2908–2917. [PubMed] [Google Scholar]
- Lund J., Dalton H. Further characterisation of the FAD and Fe2S2 redox centres of component C, the NADH:acceptor reductase of the soluble methane monooxygenase of Methylococcus capsulatus (Bath). Eur J Biochem. 1985 Mar 1;147(2):291–296. doi: 10.1111/j.1432-1033.1985.tb08749.x. [DOI] [PubMed] [Google Scholar]
- Lund J., Woodland M. P., Dalton H. Electron transfer reactions in the soluble methane monooxygenase of Methylococcus capsulatus (Bath). Eur J Biochem. 1985 Mar 1;147(2):297–305. doi: 10.1111/j.1432-1033.1985.tb08750.x. [DOI] [PubMed] [Google Scholar]
- Siegel L. M., Faeder E. J., Kamin H. Flavin interaction in NADPH-sulfite reductase. Z Naturforsch B. 1972 Sep;27(9):1087–1089. doi: 10.1515/znb-1972-0929. [DOI] [PubMed] [Google Scholar]
- Woodland M. P., Dalton H. Purification and characterization of component A of the methane monooxygenase from Methylococcus capsulatus (Bath). J Biol Chem. 1984 Jan 10;259(1):53–59. [PubMed] [Google Scholar]