Iron enzymes, binuclear non-heme

Binuclear non-heme iron enzymes are a large group of enzymes that catalyze a variety of chemical reactions and are involved in numerous metabolic functions. In this review, the structural and biochemical properties of representatives of every class of this group of enzymes are described. The contributions of electron paramagnetic resonance-related techniques to our understanding of structure and reactivity of binuclear non-heme iron enzymes are discussed, and, where appropriate, supported by data obtained from complementary spectroscopic methods. This chapter is intended as a guide to illustrate the usefulness of electron paramagnetic resonance-related techniques in the study of these enzymes. Consequently, technical details were kept to a minimum. 

Tabic 1. Representative Binuclear Non-Heme Iron Enzymes (the chemical reactions catalyzed by these enzymes and their metabolic functions are also listed)... 

EPR spectroscopy in combination with stopped-flow absorption and rapid freeze-quench techniques has been employed (i) to probe flie catalytically relevant oxidation state(s) of MIOX and (ii) to investigate the reaction between MIOX, substrate, and O2. While most other oxygen-activating binuclear non-heme iron enzymes are catalytically active in their fully reduced form, MIOX exhibits a raflier different behavior. In single-turnover reactions of the diferrous recombinant Mus... 

The reaction mechanism of ROO has not yet been studied in detail, but based on analogy with related binuclear non-heme iron enzymes, a mechanistic scheme has been proposed whereby binding of O2 to the reduced enzyme leads to the formation of a bridging peroxo intermediate, followed by the transfer of electrons from the FMN cofactor [578]. 

Wallar, BJ., and Lipscomb, J.D. Dioxygen activation by enzymes containing binuclear non-heme iron clusters, (1996) Chem. Rev. 96, 2625-2657. 

Soluble methane monooxygenase (sMMO) is the best studied binuclear non-heme iron oxygenase enzyme, largely due... 

Wallar, B. and Lipscomb, J. (1996). Dioxygen Activation by Enzymes Containing Binuclear Non-Heme Iron Clusters, Chem. Rev., 96, pp. 2625-2658. 

Iron-containing proteins are classified as heme, mononuclear non-heme, and binuclear non-heme enzymes. The Fe center... 

The active sites of binuclear non-heme enzymes consist of two Fe atoms, separated by 3 A and bridged by O-atoms derived from hydroxide or carboxylate residues (Fig. Id) (8). The iron centers can adopt 4-, 5-, or 6-coordinate geometries, with the bridging ligands bound via one or two O-atoms. The remaining coordination sites are occupied by His and Asp/Glu residues. 

The reactions of iron-containing enzymes with O2 often involve high oxidation states of the metal. Generally, the initial reaction of dioxygen with both heme and mononuclear non-heme ferrous enzymes results in the formation of Fe -superoxide intermediates. Highly reactive Fe =0 intermediates often are employed often for C-H activation. The mechanism of substrate oxidation by binuclear non-heme enzymes involves high valent, oxo-bridged species, with Fe in the -i-3 or +4 oxidation state. 

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