J. Biol. Chem., Vol. 269, Issue 23, 15993-15998, Jun, 1994
Nuclear hyperfine coupling of nitrogen in the coordination sphere of the diiron center of methane monooxygenase hydroxylase
CJ Bender, AC Rosenzweig, SJ Lippard and J Peisach
Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461.
Electron spin echo envelope modulation spectroscopy identified two ligand
14N interactions with the mixed-valence, Fe(II/III) diiron center of
methane monooxygenase hydroxylase from Methylococcus capsulatus (Bath).
Characteristic features of the spectra obtained at 9 and 10 GHz were
analyzed and fit by simulation. One of the nitrogens possessed
superhyperfine parameters (Aiso = 0.8 MHz, reff = 3.2 A, e2Qq = 1.8 MHz,
eta = 0.35) consistent with a non-coordinating amino nitrogen of a
histidine imidazole ligand to a Fe(III). The second, more strongly
interacting nitrogen (Aiso = 5.0 MHz, reff = 2.2 A, e2Qq = 3.0 MHz, eta =
0.3) corresponds to the N delta directly bound to the effective Fe(II).
These findings extend the previous electron nuclear double resonance
results on the Methylosinus trichosporium hydroxylase (Hendrich, M.P., Fox,
B.G., Andersson, K.K., Debrunner, P.G., and Lipscomb, J.D. (1992) J. Biol.
Chem. 267, 261-269), which identified the N delta-Fe(II) interaction but
failed to quantify its magnitude. Measurement of the linear electric field
g shift of this mixed-valence species indicated that the site is
charge-polarized on to one of the iron atoms, and its symmetry suggests
that either charge is shifted away from the Fe-Fe axis (if gmax is defined
by the Fe-Fe axis) or that gmid and gmax are perpendicular to the Fe-Fe
axis (charge strongly localized at Fe(III) and axis taken as gmin).
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