Moessbauer, EPR, and ENDOR studies of the hydroxylase and reductase components of methane monooxygenase from Methylosinus trichosporium OB3b

Soluble methane monooxygenase (MMO) isolated from Methylosinus trichosporium OB3b consists of three components: hydroxylase, reductase, and component B. The active-site diiron cluster of the hydroxylase has been studied with Mossbauer, ANDOR, and APR spectroscopies. Mossbauer spectra of the oxidized cluster show that the two high-spin irons are antiferromagnetically coupled in accord with our preliminary study (Fox et al. J. Biol. Chem. 1988, 263, 10553-10556). Mossbauer studies also reveal the presence of two cluster conformations at pH 9. The excited-state S=2 multiplet of the exchange-coupled cluster (Fe 3+ -Fe 3+ ) gives rise to an integer-spin EPR signal near g=8; this is the first quantitative study of such a signal from any system