Particulate methane monooxygenase (pMMO) is a membrane-bound enzyme that catalyzes the oxidation of methane to methanol in methanotropic bacteria. Understanding how this enzyme hydroxylates methane at ambient temperature and pressure is of fundamental chemical and potential commercial importance. Difficulties in solubilizing and purifying active pMMO have led to conflicting reports regarding its biochemical and biophysical properties, however. We have purified pMMO from Methylococcus capsulatus (Bath) and detected activity. The purified enzyme has a molecular mass of ~200 kDa, probably corresponding to an a2b2g2 polypeptide arrangement. Each 200 kDa pMMO complex contains 4.8 ± 0.8 copper ions and 1.5 ± 0.7 iron ions. Electron paramagnetic resonance (EPR) spectroscopic parameters corresponding to 40-60% of the total copper are consistent with the presence of a mononuclear type 2 copper site. X-ray absorption near edge (XANES) spectra indicate that purified pMMO is a mixture of Cu(I) and Cu(II) oxidation states. Finally, extended X-ray absorption fine structure (EXAFS) data are best fit with oxygen/nitrogen ligands and a 2.57 Å Cu-Cu interaction, providing the first direct evidence for a copper-containing cluster in pMMO.
Biochemistry | Molecular Biology
Lieberman, R. L., Shrestha, D. B., Doan, P. E., Hoffman, B. M., Stemmler, T. L., & Rosenzweig, A. C. (2003) PNAS 100, 3820-3825. doi:10.1073/pnas.0536703100
Feb 28 2011 (withdrawn)