Investigation of the Dinuclear Fe Center of Methane Monooxygenase by Advanced Paramagnetic Resonance Techniques: On the Geometry of DMSO Binding

Abstract

We report an extensive advanced paramagnetic resonance characterization of the mixed-valence dinuclear Fe center of methane monooxygenase hydroxylase (MMOHmv) from Methylococcus capsulatus (Mc) (Bath) and of binding to it by the exogenous ligand DMSO. We employ continuous wave and pulsed electron nuclear double resonance (ENDOR) spectroscopy, both at Q-band microwave frequencies, to examine 14,15N, 1,2H, 13C, and 57Fe nuclei. Preliminary 1H ENDOR results were communicated previously (DeRose, V. J.; Liu, K. E.; Hoffman, B. M.; Lippard, S. J. J. Am. Chem. Soc. 1993, 115, 6440−6441). ENDOR-derived 14,15N hyperfine tensors are interpreted in terms of the spin distribution on histidyl ligands bound to the dinuclear center. Determination of the 57Fe hyperfine tensors gives a complete picture of the spin-coupled Fe2+ and Fe3+ ions. The 1,2H ENDOR results disclose the presence of a bridging hydroxide and an aqua ligand in both native and DMSO-treated enzyme. A novel procedure for describing the 1H hyperfine tenso...