Prince R C, George G N, Savas J C, Cramer S P, Patel R N
Exxon Research and Engineering Co., Annandale, NJ 08801.
Biochim Biophys Acta. 1988 Jan 29;952(2):220-9. doi: 10.1016/0167-4838(88)90119-7.
The hydroxylase component of methane monooxygenase (EC 1.14.13.25), which catalyzes the oxidation of methane to methanol, has been studied by visible, electron spin resonance and X-ray spectroscopies. The enzyme appears to possess a mu-oxo- or mu-hydroxo-bridged binuclear iron site, with no sulfur ligands to the cluster. Each Fe has 4-6 oxygen (or nitrogen) ligands, at an average distance of 1.92 +/- 0.03 A. The Fe-Fe distance is 3.05 +/- 0.05 A. Essentially all of the irons are in the Fe3+ state as the enzyme is prepared, but reduction with N-methylphenazonium methosulfate generates ESR-detectable states that appear to emanate from mixed-valence binuclear sites. One of these, with gav near 1.85, displays typical Curie law microwave saturation behavior, but the other, gav near 1.73, has a very potent method of spin-relaxation. Together they account for approximately 0.6 spins per molecule.
