On the role of the axial ligand in heme-based catalysis of the peroxidase and P450 type

Rietjens, Ivonne M.C.M.; Osman, Azizah; Veeger, C.; Zakharieva, O.; Antony, Jens; Grodzicki, Michael; Trautwein, Alfred X.

doi:10.1007/s007750050068

Cited by 47 publications

(40 citation statements)

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“…In such cases, the trans influence on the intermediate can be very different from that in the reactant, resulting in an apparent mismatch between the thermodynamic and kinetic effects of the ligands. This proposal is in line with the very strong evidence for a multistep mechanism in the reactions of oxoiron(IV) porphyrin cation radicals with olefins [34][35][36][37][38][39][40][41][42]. In particular, complexes which contain both reactants in the form of either charge transfer, electron transfer, metallacycle, or radical species are frequently proposed as intermediates in these reactions.…”

Section: Scheme 5 Reaction Of the Oxoiron(iv) Tetramesitylporphyrin Cmentioning

confidence: 52%

“…Although it is generally accepted that intermediates which contain both the highvalency metalloporphyrin and the olefin must exist on the pathway to the final products (iron(III) porphyrin and the oxygenated substrate), there is no consensus about the structure of these intermediates. The most common proposals are metallacycle [35,36], charge transfer [37], electron transfer [38], or radical complexes [39] (Scheme 3). Interestingly, similar intermediates are frequently suggested to accommodate results of transition-metal-catalyzed epoxidation reactions in completely inorganic systems [40].…”

Section: Introductionmentioning

confidence: 99%

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Reaction profile of the last step in cytochrome P-450 catalysis revealed by studies of model complexes

et al. 1997

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A series of oxoiron(IV) porphyrin cation radical complexes was investigated as compound I analogs of cytochrome P-450. Both the spectroscopic features and the reactivities of the complexes in oxygen atom transfer to olefins were examined as a function of only one variable, the axial ligand trans to the oxoiron-(IV) bond. The results disclosed two important kinetic steps -electron transfer from olefin to oxoiron(IV) and intramolecular electron transfer from metal to porphyrin radical -which are affected differently by the axial ligands. The large kinetic barrier of the latter step in the reaction of olefins with the perchlorato-bound oxoiron(IV) porphyrin cation radical complex enabled the trapping of a reaction intermediate in which the metal, but not the porphyrin radical, is reduced. The first electron transfer step is probably followed by s-bond formation, which readily accounts for formation of isomerized organic products at low temperatures. It is finally postulated that part of the enhanced oxygenation activities of cytochrome P-450 monooxygenases and chloroperoxidases is due to a lowering of the energy barrier for the second electron transfer step via participation of their redox-active cysteinate ligand.

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Section: Scheme 5 Reaction Of the Oxoiron(iv) Tetramesitylporphyrin Cmentioning

confidence: 52%

Section: Introductionmentioning

confidence: 99%

Reaction profile of the last step in cytochrome P-450 catalysis revealed by studies of model complexes

et al. 1997

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“…The combined biochemical and spectroscopic evidence reported herein clearly shows that recombinant nNOS2 cannot serve as a true nitric-oxide synthase in vitro because of the abnormal heme coordination environment (e.g., see Refs. [17][18][19][20], the marked modification of the distal substrate-binding pocket, and the impairment of the formation of the active dimer. Thus, some developmental regulatory function and/or a novel physiological role (other than L-arginine-dependent NO production) should be expected for the gene product of nNOS2 in the central nervous system, and will be the subject of future investigation.…”

Section: Figmentioning

confidence: 99%

Characterization of Mouse nNOS2, a Natural Variant of Neuronal Nitric-oxide Synthase Produced in the Central Nervous System by Selective Alternative Splicing

Iwasaki¹,

Hori²,

Hayashi³

et al. 1999

Journal of Biological Chemistry

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Mouse neuronal nitric-oxide synthase 2 (nNOS2) is a unique natural variant of constitutive neuronal nitricoxide synthase (nNOS) specifically expressed in the central nervous system having a 105-amino acid deletion in the heme-binding domain as a result of in-frame mutation by specific alternative splicing. The mouse nNOS2 cDNA gene was heterologously expressed in Escherichia coli, and the resultant product was characterized spectroscopically in detail. Purified recombinant nNOS2 contained heme but showed no L-arginine-and NADPHdependent citrulline-forming activity in the presence of Ca 2؉ -promoted calmodulin, elicited a sharp electron paramagnetic resonance (EPR) signal at g ‫؍‬ 6.0 indicating the presence of a high spin ferriheme as isolated and showed a peak at around 420 nm in the CO difference spectrum, instead of a 443-nm peak detected with the recombinant wild-type nNOS1 enzyme. Thus, although the heme domain of nNOS2 is capable of binding heme, the heme coordination geometry is highly abnormal in that it probably has a proximal non-cysteine thiolate ligand both in the ferric and ferrous states. Moreover, negligible spectral perturbation of the nNOS2 ferriheme was detected upon addition of either L-arginine or imidazole. These provide a possible rational explanation for the inability of nNOS2 to catalyze the cytochrome P450-type monooxygenase reaction. Nitric-oxide synthase (NOS)1 is a complex flavo-hemoprotein that catalyzes the conversion of L-arginine to citrulline in the presence of molecular oxygen, NADPH, tetrahydrobiopterin (H 4 BP), and Ca 2ϩ -promoted calmodulin with concomitant production of nitric oxide (NO) (1-8). It is a bifunctional enzyme that is comprised of an N-terminal heme-binding domain and the C-terminal flavin-containing cytochrome P450 reductaselike domain. Ca 2ϩ -promoted calmodulin binding activates electron transfer from the flavin site to the heme site (9), where NO is produced at the heme center in the presence of oxygen, H 4 BP, and L-arginine (6,8). The heme-binding domain of NOS shows negligible structural homology to regular cytochrome P450 (6,8,10,11), although a wide range of spectroscopic evidence supports coordination of an endogenous thiolate sulfur donor ligand to the central heme iron (12-15). Recent high resolution x-ray crystal structure determinations of the monomeric and dimeric forms of the heme-binding domain fragment of inducible NOS (iNOS) have proven that the overall protein topology is very different from that of either regular cytochrome P450 or chloroperoxidase, although the proximal ligand to the central ferriheme iron is a conserved cysteine residue (10, 11). The endogenous thiolate sulfur donor ligand to the central heme iron provides a rational basis for the proposed two-step sequential catalytic mechanism of NOS, where the first step involving the formation of the intermediate N -hydroxyarginine may follow a cytochrome P450-type monooxygenase mechanism (1, 16 -20). The substrate (L-arginine) and pterin cofactor (H 4 BP) binding sites have been defin...

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“…Studies on the heme centers of the NOS isoforms by absorption, electron paramagnetic resonance (EPR), resonance Raman, and magnetic circular dichroism spectroscopy, together with mutational analysis, have strongly suggested that an endogenous thiolate sulfur donor ligand is coordinated to the central heme iron, as in the cases of cytochrome P450 and chloroperoxidase (7)(8)(9)(10)(11)(12). This was confirmed by the x-ray diffraction analysis of inducible NOS (iNOS) heme domain fragments (13,14).…”

Section: Nitric-oxide Synthase (Nos)mentioning

confidence: 65%

Modulation of the Remote Heme Site Geometry of Recombinant Mouse Neuronal Nitric-oxide Synthase by the N-terminal Hook Region

Iwasaki

Hori

Hayashi

et al. 1999

Journal of Biological Chemistry

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The role of two essential residues at the N-terminal hook region of neuronal nitric-oxide synthase (nNOS) in nitric-oxide synthase activity was investigated. Fulllength mouse nNOS proteins containing single-point mutations of Thr-315 and Asp-314 to alanine were produced in the Escherichia coli and baculovirus-insect cell expression systems. The molecular properties of the mutant proteins were analyzed in detail by biochemical, optical, and electron paramagnetic resonance spectroscopic techniques and compared with those of the wildtype enzyme. Replacement of Asp-314 by Ala altered the geometry around the heme site and the substrate-binding pocket of the heme domain and abrogated the ability of nNOS to form catalytically active dimers. Replacement of Thr-315 by Ala reduced the protein stability and altered the geometry around the heme site, especially in the absence of bound (6R)-5,6,7,8-tetrahydro-L-biopterin cofactor. These results suggest that Asp-314 and Thr-315 both play critical structural roles in stabilizing the heme domain and subunit interactions in mouse nNOS.

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On the role of the axial ligand in heme-based catalysis of the peroxidase and P450 type

Cited by 47 publications

References 0 publications

Reaction profile of the last step in cytochrome P-450 catalysis revealed by studies of model complexes

Reaction profile of the last step in cytochrome P-450 catalysis revealed by studies of model complexes

Characterization of Mouse nNOS2, a Natural Variant of Neuronal Nitric-oxide Synthase Produced in the Central Nervous System by Selective Alternative Splicing

Modulation of the Remote Heme Site Geometry of Recombinant Mouse Neuronal Nitric-oxide Synthase by the N-terminal Hook Region

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