Iron center mixed-valent form

Structure of the Iron Center Formation of the Iron Center and Tyrosyl Radical Spectroscopy of the Diferric Iron Center Spectroscopy of the Tyrosyl Radical Redox Properties of the Iron Center Mixed-Valent Form of the Iron Center Diferrous Form of the Iron Center Inhibitors to Iron-Containing Ribonucleotide Reductase Methane Monooxygenase A. Spectroscopy of the MMOH Cluster X-Ray Structure of MMOH... 

Recombinant MIOX from Mus musculus kidney was recently subjected to a detailed spectroscopic and kinetic characterization. The nature of the iron active site in the presence and absence of substrate wyo-inositol was examined using both EPR and Mfissbauer methodologies [387]. The outcome of this study has not only confirmed that MIOX contains a binuclear non-heme iron center, but also that its diiron cluster is stable in its mixed-valent form and the fully oxidized state. Specifically, the low-temperature X-band EPR spectrum of fully reduced, diferrous MIOX reveals a geff 16 resonance that disappears upon sample exposure to O2, consistent with a conversion of the diferrous center to its mixed-valent form. The... 

The use of a mixed-valent, dinuclear iron site, similar to those in hemerythrin and ribonucleotide reductase,to catalyze a nonredox reaction such as phosphate ester hydrolysis is novel and unexpected for a variant of the familiar oxo(hydroxo)-bridged diiron center. In contrast to the general agreement that exists regarding the spectroscopic and physical properties of the PAPs, their kinetics properties and especially their mechanism of action remain controversial. Much of the disagreement stems from the different pH dependences of the catalytic activity of BSPAP and Uf, which is due to the fact that the former is isolated in a proteolytically activated form while the latter is not. Proteolysis results in a substantial increase in optimal pH in addition to an increase in catalytic activity at the optimal pH. "" Current data suggest that many of the spectroscopic studies described in the literature were performed on a catalytically inactive form of the enzyme. As a result, the roles of the trivalent and divalent metal ions in catalysis and in particular the identity of the nucleophilic hydroxide that directly attacks the phosphate ester remain unresolved. 

Spectroscopic studies have demonstrated that the MMOHs have the stable diiron centers of diferric Fe(III)Fe(III), mixed-valent Fe(II)Fe(III), and diferrous Fe(II)Fe(II) redox states [33]. Although the electronic absorption spectrum of the MMOH from M. capsulatus (Bath) shows an absorption peak at 280 nm due to the protein, there is no significant optical features that can be attributed to the iron prosthetic group. The Mdssbauer Fe enriched spectrum of the isolated MMOH from M. trichosporium OB3b shows two quadrupole doublets of equal area. Their parameters at 4.2 K are AEq =1.16 mm/s and the isomer shift 5 = 0.51 mm/s for site 1 and AEq = 0.87 mm/s and the isomer shift 6 = 0.50 mm/s for site 2 [34]. The Mdssbauer spectrum of the isolated MMOH from Af. capsulatus (Bath) at 80 K shows a quadrupole doublet having AEq = 1.05 mm/s and the isomer shift 6 of 0.50 mm/s [35]. These spectra show that the isolated MMOH is diferric form. 

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