Enzymic formation of 6-oxobenzo[a]pyrene radical in rat liver homogenates from carcinogenic benzo[a]pyrene

Lesko, Stephen A.; Caspary, William J.; Lorentzen, Ronald J.; Ts’o, Paul O. P.

doi:10.1021/bi00689a008

Cited by 123 publications

(30 citation statements)

References 12 publications

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“…It is tempting to speculate that cytochrome P450 catalyzes HETE formation from arachidonic acid by a mechanism similar to a lipoxygenase-catalyzed reaction (21). In the present case, the initial hydrogen abstraction may be analogous to the electron transfer shown to occur with substrates such as benzo[a]pyrene and aminopyrine (22,23). The 15-keto-5,8,11,13-icosatetraenoic acid may be derived from 15-HPETE, implying the formation of a hydroperoxide in the incubation mixture.…”

Section: Methodsmentioning

confidence: 78%

“…2) cochromatographs on both types ofHPLC columns with a sample of 15-HETE biosynthesized by incubating arachidonic acid with soybean lipoxygenase. Of interest is the observation that the metabolites associated with peak 11 can be resolved by chromatography using the lPorasil column into a metabolite that elutes close to fraction 22 (peak A ofFig. 2) and absorbs light at 285 nm and a metabolite that elutes close to fraction 110 (peak G of Fig.…”

Section: Methodsmentioning

confidence: 99%

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Cytochrome P-450-dependent oxygenation of arachidonic acid to hydroxyicosatetraenoic acids.

Capdevila¹,

Marnett²,

Chacos³

et al. 1982

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

141

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Arachidonic acid is oxidized by a NADPH-dependent oxygenase of rat liver microsomes to a number ofoxygencontaining products, which can be resolved by HPLC. Several of these products have been purified and characterized. They exhibit an absorbance in the UV region of the spectrum that has a maximum at =235 nm, indicative ofthe presence ofa conjugated diene function. Mass spectral analysis of the trimethylsilyl ether derivatives of the methyl esters of the hydrogenated and nonhydrogenated metabolites shows that they are the 9-, 11-, 12-, and 15-monohydroxy derivatives of arachidonic acid, the hydroxyicosatetraenoic acids (HETEs). Their UV absorbance and chromatographic properties suggest that these products possess cis,transdiene geometry characteristic ofHETEs isolated from other mammalian sources. The isolation of these isomeric HETEs suggests that cytochrome P-450 may play a role in the oxidative metabolism of arachidonic acid to physiologically and pharmacologically important hydroxylated unsaturated fatty acids.The oxygenation of arachidonic acid to hydroxyicosatetraenoic acids (HETEs), which contain a conjugated diene function, is catalyzed by enzyme(s) present in several mammalian tissues and has important pathophysiological consequences (1, 2). The isolation of each of the isomeric HETEs has been reported, although significant tissue variation in the composition of the products formed has been observed (3-6). HETEs and their hydroperoxy acid precursors (HPETEs) exhibit diverse biological activities and may play an important role in leukocyte chemotaxis and the inflammatory response (1).HETEs are produced by an oxygenation reaction involving either lipoxygenases (3), singlet molecular oxygen (7), or autooxidation (8). Animal lipoxygenases have not been extensively purified and the nature and properties of this class of mammalian enzymes have scarcely been characterized in most tissues that biosynthesize HETEs. We have recently reported a novel route for the oxidative metabolism ofarachidonic acid (9). The reaction is catalyzed by liver microsomes and requires NADPH and molecular oxygen. The reaction is inhibited by carbon monoxide and metyrapone, suggesting a role for microsomal cytochrome P450 (9). The metabolism ofarachidonic acid can also be demonstrated in reconstitution experiments using purified cytochromes P450 and NADPH-cytochrome P-450 reductase (10).The present paper describes studies to characterize some of the metabolites formed during the rat liver microsomal cytochrome P450-dependent oxidation of arachidonic acid. We report here that the major components of that group of products are the 9-, 11-, 12-, and 15-hydroxy derivatives of arachidonic acid-the HETEs. MATERIALS AND METHODSMicrosomal fractions were prepared from homogenates of rat livers as described (11). Male Sprague-Dawley rats (150-200 g body weight) were treated by four daily intraperitoneal injections ofphenobarbital (75 mg/kg ofbody weight) and starved overnight prior to sacrifice.The oxygenation products of arachidonic m...

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Section: Methodsmentioning

confidence: 78%

Section: Methodsmentioning

confidence: 99%

Cytochrome P-450-dependent oxygenation of arachidonic acid to hydroxyicosatetraenoic acids.

Capdevila¹,

Marnett²,

Chacos³

et al. 1982

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

141

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“…6-Hydroxy-BaP is not detected as a stable metabolite of BaP, and Nagata et al were the first to show that its presence could be detected by observation of the EPR signal of the 6-oxy-BaP radical in rat liver homogenate metabolism of BaP (3,42). Ts'o et al (8,9) showed that the EPR signal obtained with BaP is identical to that obtained from chemical and enzymatic oxidation of 6-hydroxy-BaP. It was also shown that the 6-hydroxy-BaP was the precursor of most, if not all, of the BaP-diones (1,6-, 6,12-, and 3,6-) formed during the metabolism of BaP (9).…”

Section: Oxygenated Bap Radicalsmentioning

confidence: 86%

“…The free-radical or one-electron oxidation pathway involves the enzymatic formation of 6-hydroxy-BaP via a direct oxygen insertion mediated by cytochrome-P-450, or possibly via the reaction of the enzymatically formed BaP cation radical with water. The 6-hydroxyBaP is then rapidly oxidized in several one-electron steps via an intermediate radical identified as 6-oxyBaP, (the phenoxy radical derived from 6-hydroxyBaP), to produce a mixture of 1,6-,3,6-, and 6,12-BaPdiones (3,8,9,11). 6-Hydroxy-BaP is not detected as a stable metabolite of BaP, and Nagata et al were the first to show that its presence could be detected by observation of the EPR signal of the 6-oxy-BaP radical in rat liver homogenate metabolism of BaP (3,42).…”

Section: Oxygenated Bap Radicalsmentioning

confidence: 99%

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Free Radicals of Benzo(a)pyrene and Derivatives

Sullivan¹

1985

Environmental Health Perspectives

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Oxidation of Benzo(a) Pyrene Catalyzed by Phenol Oxidases of Alga Nitella sp. and Potato Tubers

Кирсо

Belykh

Стом

1981

Acta hydrochim. hydrobiol.

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Sunzmary:The kinetics of oxidation of carcinogenic benzo(a)pyrene (0.1 nM solution in phosphate buffer) catalyzed by enzyme protein of soil and water plants (potato tubers and alga Nitetla sp.) has been studied. The benzo(a)pyrene oxidation rate is determined by the phenoloxidase activity of the enzyme protein from both sources to a n equal degree and expressed by the Michaelis-Menten equation. The values for kcat and apparent Km were (0.97k0.14) Ms-1 and 33+GyM, respectively.The presence of other compounds (including protein substances) in acetone preparations of potato tubers considerably suppresses its catalytic activity in relation to benzo(a)pyrene.Consequently, in the polluted biosphere some water plants. such as alga Nitella sp., and potato tuber can transform carcinogenic benzo(a)pyrene (BP).As oxidation products, all three BP-quinoncs, i.e. 1,6-, 3,6and 6,12-diones, were identified.

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Enzymic formation of 6-oxobenzo[a]pyrene radical in rat liver homogenates from carcinogenic benzo[a]pyrene

Cited by 123 publications

References 12 publications

Cytochrome P-450-dependent oxygenation of arachidonic acid to hydroxyicosatetraenoic acids.

Cytochrome P-450-dependent oxygenation of arachidonic acid to hydroxyicosatetraenoic acids.

Free Radicals of Benzo(a)pyrene and Derivatives

Oxidation of Benzo(a) Pyrene Catalyzed by Phenol Oxidases of Alga Nitella sp. and Potato Tubers

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