Heme-Containing Oxygenases

Sono, Masanori; Roach, Mark P.; Coulter, Eric D.; Dawson, John H.

doi:10.1021/cr9500500

Cited by 2,275 publications

(2,292 citation statements)

References 350 publications

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“…Although the strong electron donating ability of thiolate favors heterolytic cleavage of the O-O bond of hydroperoxides [30], P450s are also capable of catalyzing homolytic cleavage. It appears that the nature of the substrate, active site environment and heme conformation each plays a different role in determining the fate of O-O bond cleavage.…”

Section: Discussionmentioning

confidence: 99%

Reaction mechanisms of 15-hydroperoxyeicosatetraenoic acid catalyzed by human prostacyclin and thromboxane synthases

Yeh¹,

Tsai²,

Wang³

2007

Archives of Biochemistry and Biophysics

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Prostacyclin synthase (PGIS) and thromboxane synthase (TXAS) are atypical cytochrome P450s. They do not require NADPH or dioxygen for isomerization of prostaglandin H 2 (PGH 2 ) to produce prostacyclin (PGI 2 ) and thromboxane A 2 (TXA 2 ). PGI 2 and TXA 2 have opposing actions on platelet aggregation and blood vessel tone. In this report, we use a lipid hydroperoxide, 15-hydroperoxyeicosatetraenoic acid (15-HPETE), to explore the active site characteristics of PGIS and TXAS. The two enzymes transformed 15-HPETE not only into 8,, like many microsomal P450s, but also to 15-ketoeicosatetraenoic acid (15-KETE) and 15-hydroxyeicosatetraenoic acid (15-HETE). 13-OH-14,15-EET and 15-KETE result from homolytic cleavage of the O-O bond, whereas 15-HETE results from heterolytic cleavage, a common peroxidase pathway. About 80% of 15-HPETE was homolytically cleaved by PGIS and 60% was homolytically cleaved by TXAS. The V max of homolytic cleavage is 3.5-fold faster than heterolytic cleavage for PGIS-catalyzed reactions (1100 min −1 vs. 320 min −1 ) and 1.4-fold faster for TXAS (170 min −1 vs. 120 min −1 ). Similar K M values for homolytic and heterolytic cleavages were found for PGIS (∼60 μM 15-HPETE) and TXAS (∼80 μM 15-HPETE), making PGIS a more efficient catalyst for the 15-HPETE reaction.Keywords prostacyclin synthase; thromboxane synthase; cytochrome P450; peroxide bond cleavage; homolytic; heterolytic; hydroperoxides; epoxyalcohol Prostacyclin synthase (PGIS) and thromboxane synthase (TXAS) are members of the cytochrome P450 superfamily, which uses heme as the prosthetic group and has a cysteine thiolate proximal ligand [1,2]. PGIS and TXAS convert prostaglandin H 2 (PGH 2 ) to prostacyclin (PGI 2 ) and thromboxane A 2 (TXA 2 ), respectively. PGI 2 inhibits platelet activation and aggregation and induces vasodilation, whereas TXA 2 stimulates platelet secretion, aggregation and vasoconstriction [3]. Both PGI 2 and TXA 2 are rapidly hydrolyzed To whom correspondence should be addressed: Lee-Ho Wang Division of Hematology Department of Internal Medicine 6431 Fannin Houston, TX 77030 Tel: 713-500-6794 Fax: 713-500-6810 e-mail: lee-ho.wang@uth.tmc.edu 1 The abbreviations used are: PGIS, prostacyclin synthase; PGI 2 , prostacyclin; PGHS, prostaglandin H synthase; TXAS, thromboxane synthase; TXA 2 , thromboxane A 2 ; 8,11-eicosatrienoic acid; ESI/MS, electron-spray ionization/ mass spectrometry; EPR, electron paramagnetic resonance; SVD, singular value decomposition.Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Hecker and Ullrich proposed a caged radical mechanism for TXAS ...

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Section: Discussionmentioning

confidence: 99%

Reaction mechanisms of 15-hydroperoxyeicosatetraenoic acid catalyzed by human prostacyclin and thromboxane synthases

Yeh¹,

Tsai²,

Wang³

2007

Archives of Biochemistry and Biophysics

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“…each excited state was converged fixed in the ground state geometry, and the energy difference between this electronic excited state and the ground state was calculated, ΔE = E (es) -E(gs). In addition, the geometry of the excited state with the electronic configuration d (xy) 1 d(xz/yz) 3 was optimized, the wave function converged, but fixed in this electronic excited state. Thus, the structure of the geometrically relaxed excited state was obtained.…”

Section: Electronic Structure Calculationsmentioning

confidence: 99%

Spectroscopic and Quantum Chemical Studies on Low-Spin Fe^IVO Complexes: Fe−O Bonding and Its Contributions to Reactivity

et al. 2007

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High valent Fe IV =O species are key intermediates in the catalytic cycles of many mononuclear nonheme iron enzymes and have been structurally defined in model systems. Variable temperature magnetic circular dichroism (VT-MCD) spectroscopy has been used to evaluate the electronic structures and in particular the Density Functional calculations were correlated to the data and support the experimental analysis. The strength and covalency of the Fe-O π-bond result in high oxygen character in the important frontier molecular orbitals (FMOs) for this reaction, the unoccupied β-spin d(xz/yz) orbitals, and activates these for electrophilic attack. An extension to biologically relevant Fe IV =O (S=2) enzyme intermediates shows that these can perform electrophilic attack reactions along the same mechanistic pathway (π-FMO pathway) with similar reactivity, but also have an additional reaction channel involving the unoccupied α-spin d(z 2 ) orbital (σ-FMO pathway).These studies experimentally probe the FMOs involved in the reactivity of Fe IV =O (S=1) model complexes resulting in a detailed understanding of the Fe-O bond and its contributions to reactivity.

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“…cytochromes a, b, c and f) [1][2][3] which cycle between low-spin Fe(II) and low-spin Fe(III), small molecule binding and transport, 4,5 catalysis and O 2 activation (e.g. peroxidases and cytochromes P450) [6][7][8][9][10][11] where high valent Fe centers are involved in H atom abstraction, hydroxylation and epoxide formation. Heme sites are fundamentally different from non-heme iron sites in that the porphyrin ligand allows for the delocalization of the iron d electrons into the porphyrin π system.…”

Section: Introductionmentioning

confidence: 99%

“…[12][13][14] This changes the nature of the Fe in terms of the flexibility of the central coordination site, the energetics of reactivity, and its function in electron transfer (ET). 11 Heme enzymes have been easier to study than non-heme Fe enzymes because of the intense characteristic porphyrin π → π* transitions. However, these transitions have made studying the metal center difficult because they obscure many of the spectral properties of the Fe sites.…”

Section: Introductionmentioning

confidence: 99%

Fe L-Edge X-ray Absorption Spectroscopy of Low-Spin Heme Relative to Non-heme Fe Complexes: Delocalization of Fe d-Electrons into the Porphyrin Ligand

et al. 2006

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Hemes (iron porphyrins) are involved in a range of functions in biology including electron transfer, small molecule binding and transport, and O 2 activation. The delocalization of the Fe d-electrons into the porphyrin ring and its effect on the redox chemistry and reactivity of these systems has been difficult to study by optical spectroscopies due to the dominant porphyrin π → π* transitions which obscure the metal center. Recently we have developed a methodology that allows for the interpretation of the multiplet structure of Fe L-edges in terms of differential orbital covalency (i.e. differences in mixing of the d-orbitals with ligand orbitals) using a valence bond configuration interaction (VBCI) model. Applied to low spin heme systems, this methodology allows experimental determination of the delocalization of the Fe d-electrons into the porphyrin (p) ring both in terms of P→Fe σ and π donation and Fe→P π back-bonding. We find that π donation to Fe(III) is much larger than π back-bonding from Fe(II), indicating that a hole super-exchange pathway dominates electron transfer. The implications of the results are also discussed in terms of the differences between heme and non-heme oxygen activation chemistry.

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Heme-Containing Oxygenases

Cited by 2,275 publications

References 350 publications

Reaction mechanisms of 15-hydroperoxyeicosatetraenoic acid catalyzed by human prostacyclin and thromboxane synthases

Reaction mechanisms of 15-hydroperoxyeicosatetraenoic acid catalyzed by human prostacyclin and thromboxane synthases

Spectroscopic and Quantum Chemical Studies on Low-Spin Fe^IVO Complexes: Fe−O Bonding and Its Contributions to Reactivity

Fe L-Edge X-ray Absorption Spectroscopy of Low-Spin Heme Relative to Non-heme Fe Complexes: Delocalization of Fe d-Electrons into the Porphyrin Ligand

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Heme-Containing Oxygenases

Cited by 2,275 publications

References 350 publications

Reaction mechanisms of 15-hydroperoxyeicosatetraenoic acid catalyzed by human prostacyclin and thromboxane synthases

Reaction mechanisms of 15-hydroperoxyeicosatetraenoic acid catalyzed by human prostacyclin and thromboxane synthases

Spectroscopic and Quantum Chemical Studies on Low-Spin FeIVO Complexes: Fe−O Bonding and Its Contributions to Reactivity

Fe L-Edge X-ray Absorption Spectroscopy of Low-Spin Heme Relative to Non-heme Fe Complexes: Delocalization of Fe d-Electrons into the Porphyrin Ligand

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Spectroscopic and Quantum Chemical Studies on Low-Spin Fe^IVO Complexes: Fe−O Bonding and Its Contributions to Reactivity