The status of high-valent metal oxo complexes in the P450 cytochromes

Makris, Thomas M.; Köenig, Konstanze von; Schlichting, Ilme; Sligar, Stephen G.

doi:10.1016/j.jinorgbio.2006.01.025

Cited by 110 publications

(91 citation statements)

References 99 publications

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“…It seems that the features of P450 intermediates depend on a great number of small differences in structure from one protein to another. Recently, a Cpd I of Fe (IV)=O complexed with an amino acid radical was identified in P450cam and P450BM3 upon reaction with peracetic acid or m-chloroperbenzoic acid [36,37]. We also observed that the reaction of PGIS with peracetic acid produced a metastable intermediate with spectral features similar to Cpd I (Yeh and Wang, unpublished results), indicating that both Cpd I and Cpd II can be major intermediates for PGIS.…”

Section: Discussionmentioning

confidence: 57%

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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: 57%

mentioning

confidence: 58%

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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“…The calculations show that in both hIDO and xcTDO, the dioxygen gains superoxide character upon binding to the heme iron, as evident by the negative charges on O 2 addition, as illustrated in Fig. 5, in both enzymes the ferric hemebound superoxide in the active ternary complex can be readily inserted into the C 2 ϭC 3 bond of the indole ring, without the deprotonation of the indoleamine, giving rise to the 2-alkylperoxo transition state, in which the C 2 atom assumes a sp 3 configuration, while the C 3 atom retains the sp 2 configuration with a radical associated with it.…”

Section: Resultsmentioning

confidence: 97%

“…Despite decades of effort, the mechanism by which dioxygen is activated and inserted into the substrate in the dioxygenase reactions is not known, presenting a major knowledge gap in heme oxygen chemistry. Nonetheless, it is generally believed that the 2 atoms of the dioxygen are simultaneously incorporated into the substrate, setting it apart from monooxygenase reactions (1)(2)(3).…”

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confidence: 99%

Evidence for a ferryl intermediate in a heme-based dioxygenase

Lewis-Ballester

Batabyal

Egawa

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

118

217

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In contrast to the wide spectrum of cytochrome P450 monooxygenases, there are only 2 heme-based dioxygenases in humans: tryptophan dioxygenase (hTDO) and indoleamine 2,3-dioxygenase (hIDO). hTDO and hIDO catalyze the same oxidative ring cleavage reaction of L-tryptophan to N-formyl kynurenine, the initial and rate-limiting step of the kynurenine pathway. Despite immense interest, the mechanism by which the 2 enzymes execute the dioxygenase reaction remains elusive. Here, we report experimental evidence for a key ferryl intermediate of hIDO that supports a mechanism in which the 2 atoms of dioxygen are inserted into the substrate via a consecutive 2-step reaction. This finding introduces a paradigm shift in our understanding of the heme-based dioxygenase chemistry, which was previously believed to proceed via simultaneous incorporation of both atoms of dioxygen into the substrate. The ferryl intermediate is not observable during the hTDO reaction, highlighting the structural differences between the 2 dioxygenases, as well as the importance of stereoelectronic factors in modulating the reactions. indoleamine 2,3-dioxygenase ͉ reasonance Raman spectroscopy ͉ tryptophan dioxygenase

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“…This analysis resulted in an apparent k cat1 of 1.3 ± 0.2 s −1 , K m1 of 9 ± 4 μM, and k cat2 /K m2 of 0.96 min −1 μM −1 at 500 μM H 2 O 2 ( (27), chloroperoxidases (28), P450s (29)(30)(31)] is well known; however, the mechanisms and products of these reactions differ. Nevertheless, catalysis by both oxygenases and peroxidases involves conversion of the ferric enzyme to the principal reactive intermediate compound I (32)(33)(34)(35).…”

mentioning

confidence: 99%

Indole peroxygenase activity of indoleamine 2,3-dioxygenase

Kuo

Mauk

2012

Proc. Natl. Acad. Sci. U.S.A.

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The heme enzyme indoleamine 2,3-dioxygenase (IDO) was found to catalyze the oxidation of indole by H 2 O 2 , with generation of 2-and 3-oxoindole as the major products. This reaction occurred in the absence of O 2 and reducing agents and was not inhibited by superoxide dismutase or hydroxyl radical scavengers, although it was strongly inhibited by L-Trp. The stoichiometry of the reaction indicated a one-to-one correspondence for the consumption of indole and H 2 O 2 . The 18 O-labeling experiments indicated that the oxygen incorporated into the monooxygenated products was derived almost exclusively from H 2 18 O 2 , suggesting that electron transfer was coupled to the transfer of oxygen from a ferryl intermediate of IDO. These results demonstrate that IDO oxidizes indole by means of a previously unrecognized peroxygenase activity. We conclude that IDO inserts oxygen into indole in a reaction that is mechanistically analogous to the "peroxide shunt" pathway of cytochrome P450.monooxygenase | oxygen isotopic labeling T he heme enzyme indoleamine 2,3-dioxygenase (IDO) catalyzes the first and rate-determining step of L-tryptophan metabolism in nonhepatic mammalian tissues by inserting both atoms of O 2 into the indole ring to form N-formylkynurenine (N-FK) (1). This dioxygenase activity of IDO requires O 2 and the reduced (Fe 2+ ) enzyme or O 2•− and the oxidized (Fe 3+ ) enzyme. In recent years, an increasing number of physiological consequences of IDO activity have been identified, including links to neural, ocular, and immunological disorders (2). Of these roles, the ability of IDO expressed by tumors to suppress the normal response of T lymphocytes and enable tumor survival and growth has attracted the most intense interest, owing to its implications for the development of new therapeutic approaches in cancer treatment (3).Aside from tryptophan (Trp), the dioxygenase activity of IDO extends to oxidation of other indoleamines, such as 5-hydroxy-LTrp, serotonin, and tryptamine, whereas indole, 3-methylindole, and indoleacetic acid are not substrates (4-6). Although indole can apparently bind to the oxygenated enzyme (IDOFe 3+ -O 2•− ) or to the IDOFe 2+ -CO complex (7), autoxidation to IDOFe 3+ is unaffected by the presence of indole, and oxidation of indole does not occur (5). Notably, IDO does not catalyze oxidation of L-Trp by H 2 O 2 (4, 8, 9). Consequently, the reactivity of IDO with H 2 O 2 received little attention for more than 30 years. During that time, IDO was noted to have peroxidase activity (6) and to catalyze the H 2 O 2 -supported N-demethylation of benzphetamine and hydroxylation of aniline (10), but these activities were not studied further.Recently, reactivity of the enzyme with H 2 O 2 has received considerable attention in light of spectroscopic detection of a compound II-like ferryl species (11, 12) and quantum mechanics/ molecular mechanics simulations implicating a role for this intermediate in the catalytic cycle (13). Subsequently, the peroxidase activity of IDO has received renewed atten...

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The status of high-valent metal oxo complexes in the P450 cytochromes

Cited by 110 publications

References 99 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

Evidence for a ferryl intermediate in a heme-based dioxygenase

Indole peroxygenase activity of indoleamine 2,3-dioxygenase

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