Spectroscopic studies of the non-heme ferric active site in soybean lipoxygenase: magnetic circular dichroism as a probe of electronic and geometric structure. Ligand-field origin of zero-field splitting

Abstract

a preconditioned all-glass ampoule equipped with a break-seal, in accordance with the sort of procedures that were adopted for the synthesis and isolation of the gallane (q.v.); subsequent manipulation and analysis of the reaction mixture could usually be accomplished using a more conventional vacuum line having a distillation train and greased ground-glass or, if necessary, greaseless stopcocks as well as ground-glass joints lubricated typically with Apiezon L grease. In none of the experiments was there any evidence that unchanged gallane survived the encounter with an excess of the reagent (HC1, NMe3, NH3, PH3, or C2H4) under the conditions outlined in the preceding section.All noncondensable gases-Ar, Kr, and N2 (research grade)-were used as received from the British Oxygen Co. (B.O.C.). The following reagents, from the commercial sources indicated, were purified before use by fractionation in vacuo: HC1 (Air Products), NH3 (B.O.C.), and C2H4 (B.O.C.). Toluene-</8 and benzent-d6, both supplied by Aldrich, were dried and fractionated in vacuo prior to use as NMR solvents. Phosphine was prepared by the action of aqueous hydrochloric acid on calcium phosphide (Ventrón), trimethylamine by the action of alkali on trimethylammonium chloride (Aldrich); fractional condensation of each of these reagents in vacuo gave a sample judged to be pure by the criteria of tensimetric and IR measurements.Acknowledgment. This work was supported by the S.E.R.C. through a research grant, through the award of research studentships (to M.J.G. and C.R.P.), through funding of the Edinburgh Electron-Diffraction Service (including H.E.R.'s research assistantship), and through provision of the microdensitometer facilities at Daresbury. We thank Professor I. M. Mills for much practical assistance and advice concerning the IR spectrum and vibrational analysis of Ga2H6, and also acknowledge with gratitude the contributions of Dr. P. L. Baxter (who carried out the early experiments with gallium(III) chloride and metal tetrahydridogallates) and Mr. P. T. Brain (for assistance with the NMR measurements).

Magnetic Parameters and Magnetic Functions in Mononuclear Complexes Beyond the Spin-Hamiltonian Formalism

“…The derivation is consistent with the result of Solomon et al [86]. A detailed inspection to the lowest CFMs, calculated in the complete d 5 space spanned by 252 functions, shows a small splitting of δ 78 = Γ 8 -Γ 7 = 0.0011 cm -1 (Table 74, Fig.…”

Simulation of the EMR Spectra of High-Spin Iron in Proteins

“…(1981) were approximately equal, although two near-axial components were included. D values on the order of 2 em-I for lipoxygenase samples with both symmetries have been confirmed in recent EPR and MCD studies (Zhang et al, 1991;Whittaker and Solomon, 1988). In our laboratory, we have sought to understand the role of oxygen in preparing ferric lipoxygenase samples and to establish biochemical conditions that favor a preponderance of the more rhombic species (Mavrophilipos, 1986;Gaffney, 1990;Gaffney et al, 1993).…”

Construction of a catalytically active iron superoxide dismutase by rational protein design

“…The electronic absorption spectra of high-spin d 5 (Fe 3ϩ ) centers are typically dominated by the spin-allowed ( M Ͼ 1000) LMCT transitions originating from relatively easily oxidized ligands such as histidine (28,29). Electronic transitions arising from within the d-orbital manifold (ligand field) are all spin-forbidden and are therefore much less intense ( M Ͻ 500).…”