Methane monooxygenase

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Ammonia monooxygenase
File:1yew opm.gif
OPM superfamily23
OPM protein1yew

Methane monooxygenase, or MMO, is an enzyme capable of oxidizing the C-H bond in methane as well as other alkanes. Methane monooxygenase belongs to the class of oxidoreductase enzymes (EC

There are two well-studied forms of MMO: the soluble form (sMMO) and the particulate form (pMMO). The active site in sMMO contains a di-iron center bridged by an oxygen atom (Fe-O-Fe), whereas the active site in pMMO utilizes copper. Structures of both proteins have been determined by X-ray crystallography; however, the location and mechanism of the active site in pMMO is still poorly understood and is an area of active research.

The particulate methane monooxygenase and related ammonia monooxygenase are integral membrane proteins, occurring in methanotrophs and ammonia oxidisers, respectively, which are thought to be related[1]. These enzymes have a relatively wide substrate specificity and can catalyse the oxidation of a range of substrates including ammonia, methane, halogenated hydrocarbons, and aromatic molecules[2]. These enzymes are composed of 3 subunits - A (InterPro: IPR003393), B (InterPro: IPR006833) and C (InterPro: IPR006980) - and contain various metal centers, including copper. Particulate methane monooxygenase from Methylococcus capsulatus is an ABC homotrimer, which contains mononuclear and dinuclear copper metal centers, and a third metal center containing a metal ion whose identity in vivo is not certain[3].

The A subunit from Methylococcus capsulatus (Bath) resides primarily within the membrane and consists of 7 transmembrane helices and a beta-hairpin, which interacts with the soluble region of the B subunit. A conserved glutamate residue is thought to contribute to a metal center[3].

Methane monooxygenases are found in methanotrophic bacteria, a class of bacteria that exist at the interface of aerobic (oxygen-containing) and anaerobic (oxygen-devoid) environments. One of the more widely-studied bacteria of this type is Methylococcus capsulatus (Bath). This bacterium was discovered in the hot springs of Bath, England.

See also


  1. Murrell JC, Lidstrom ME, Holmes AJ, Costello A (1995). "Evidence that particulate methane monooxygenase and ammonia monooxygenase may be evolutionarily related". FEMS Microbiol. Lett. 132 (3): 203–208. PMID 7590173.
  2. Sayavedra-soto LA, Hommes NG, Arp DJ (2002). "Molecular biology and biochemistry of ammonia oxidation by Nitrosomonas europaea". Arch. Microbiol. 178 (4): 250–255. PMID 12209257.
  3. 3.0 3.1 Lieberman RL, Rosenzweig AC (2005). "Crystal structure of a membrane-bound metalloenzyme that catalyses the biological oxidation of methane". Nature. 434 (7030): 177–182. PMID 15674245.

Further reading

  • J.J.R. Fraústo da Silva and R.J.P. Williams, The biological chemistry of the elements: The inorganic chemistry of life, 2nd Edition, Oxford University Press, 2001, ISBN 0-19-850848-4

External links


This article incorporates text from the public domain Pfam and InterPro: IPR003393