Non-heme iron enzymes

Oxygen activation is a central theme in biochemistry and is performed by a wide range of different iron and copper enzymes. In addition to our studies of the dinuclear non-heme iron enzymes MMO and RNR, we also studied oxygen activation in the mononuclear non-heme iron enzyme isopenicillin N synthase (IPNS). This enzyme uses O2 to transform its substrate ACV to the penicillin precursor isopenicillin N [53], a key step in the synthesis of the important P-lactam antibiotics penicillins and cephalosporins [54, 55],... 

The active-site model (and the ONIOM model system) includes Fe, one aspartate and two histidine ligands, a water ligand and selected parts of the substrate (see Figure 2-6). The 2-histidine-1-carboxylate ligand theme is shared by several other non-heme iron enzymes [59], For the protein system, we used two different... 

Emerson, J.P., Farquhar, E.R. and Que, L. Jr. (2007) Structural snapshots along reaction pathways of non-heme iron enzymes. Angewandte Chemie, International Edition, 46, 8553-8556. 

The A, AT, 0-binding motif is found in many non-heme iron enzymes as well as in some zinc enzymes as metal-binding motif Thus, to mimic this motif is the purpose of small organic 0-ligands such as... 

D. Other Dioxygen Activating Mononuclear Non-Heme Iron Enzymes... 

Solomon El, Brunold TC, Davis MI, et al. Geometric and electronic structure/function correlations in non-heme iron enzymes. Chern Rev 100 235-349,2000. 

Various alkane oxidations are catalyzed by iron complexes. Such reactions are important in view of the action of non-heme iron enzymes, such as methane monooxygenase, in hydrocarbon oxidations in biological systems. For example, the oxo-bridged complex [Fe2(TPA)2(ju,-0)(ju.-0Ac)]3+ [TPA = tris(2-pyridylmethyl)-amine] catalyzes the oxidation of cyclohexane with Bu OOH. Related complexes with an Fein2(/i-0)(/i-0Ac)2 core oxidize cyclohexane or adamantane to give a mixture of alcohols and ketones.159 Less well defined systems, e.g., FeCl3-6H20/ aldehyde/AcOH/02 are similarly active.160... 

D. S. Marlin and P. K. Mascharak, Biomimetic Catalysis by Models of Non-Heme Iron Enzymes in Encyclopedia of Catalysis , ed. I. T. Horvath, John Wiley and Sons, Inc., New York, 2004. 

Zhou J, Kelly WL, Bachmmann BO, Gunsior M, Townsend CA, Solomon EL Spectroscopic studies of substrate interactions with clavaminate synthase 2, a multifunctional alpha-KG-dependent non-heme iron enzyme correlation with mechanisms and reactivities. J. Am. Chem. Soc. 2001 123 7388-7398. 

Figure 3 Illustration of possible partial reaction cycles of some oxygenase enzymes. Water molecules and protein ligands have sometimes been omitted for clarity, (a) P450 (18) (b) intradiol dioxygenase (7) (c) lipoxygenase (7) (d) a-KG-dependent non-heme Iron enzymes (14) (e) soluble methane monooxygenase (15) (f) uncoupled blnuclear copper (16) (g) coupled blnuclear copper (h) flavin monooxygenases (17).

As mentioned, many non-heme iron enzymes also catalyze oxidase-type reactions, such as desaturation, in biological systems (7). Similar to the non-heme iron oxygenases, the reactions are thought to proceed through an Fe =0 intermediate. Two examples of enzymes that catalyze biologically interesting oxidase reactions are isopenicillin N-synthase (IPNS) and 1-aminocyclopropane-l-carboxylate oxidase (ACCO). 

Solomon El, Decker A, Lehnert N. Non-heme iron enzymes contrasts to heme catalysis. Proc. Natl. Acad. Sci. 2003 100 3589-3594. 

Isopenicillin N synthase (IPNS) is a mononuclear non-heme iron enzyme that plays an important role for biosynthesis of antibiotics [85]. Using one O2 molecule, the enzyme catalyzes the bicyclic ring closure of the substrate (5-(L-Q -aminoadipoyl)-L-cysteinyl-D-valine (ACV) to form two water molecules eind isopenicilUn N (IPN), a precursor of the cintibiotics peni-... 

LeCloux, D. D. Barrios, A. M. Mizoguchi, T. J. Lippard, S. J. Modeling the diiron centers of non-heme iron enzymes. Preparation of sterically hindered diiron(II)... 

High-valent iron-oxo intermediates are commonly invoked in catalytic cycles of mononuclear iron enzymes that activate O2 to effect metabolically important oxidative transformations. Catalytic pathways of many mononuclear non-heme iron enzymes are proposed to involve high-valent iron-oxo intermediates as the active oxidizing species. Two isomeric pentadentate bispidine Fe(II) complexes (bispi-dine = 3,7 - diazabicyclo l,3,3,nonane) in the presence of H2O2 are catalytically active for the epoxidation and 1,2-dihydroxylation of cyclooctene [78, 79]. Spectral and mechanistic studies indicate that in all these cases a Fe(IV) = O intermediate is responsible for the catalytic process [80]. 

Metalloenzymes containing non-heme iron centers are widespread in nature. Several members of this family isolated from mammals, plants, or bacteria, have now been structurally characterized (4). In addition to the crystal structures for the isolated resting states, an increasing amount of spectroscopic information has become available concerning the active sites of these iron enzymes (25-27). The non-heme iron enzymes perform a broad range of functions, but most important is their role in the activation of dioxygen for... 

A. Masschelein, A. L. Feig, and S. J. Lippard. Oxidation mechanisms of diiron(II) model compounds of non-heme iron enzymes by oxygen, submitted for publication. 

IRON COMPLEXES OF CYCLAM AND CYCLAM-LIKE LIGANDS AS MODELS FOR NON-HEME IRON ENZYMES... 

Further study of the iron complexes of cyclam and cyclam like ligands may provide new insight into the mechanism of non-heme iron enzymes. 

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