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  Isotope effects and intermediates in the reduction of NO by P450NOR

Daiber, A., Nauser, T., Takaya, N., Kudo, T., Weber, P., Hultschig, C., Shoun, H., & Ullrich, V. (2001). Isotope effects and intermediates in the reduction of NO by P450NOR. Journal of Inorganic Biochemistry, 88(3 - 4), 343-352.

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アイテムのパーマリンク: https://hdl.handle.net/11858/00-001M-0000-0010-8CD5-D 版のパーマリンク: https://hdl.handle.net/11858/00-001M-0000-0010-8CD6-B
資料種別: 学術論文

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 作成者:
Daiber, A., 著者
Nauser, T., 著者
Takaya, N., 著者
Kudo, T., 著者
Weber, P., 著者
Hultschig, C.1, 著者
Shoun, H., 著者
Ullrich, V., 著者
所属:
1Max Planck Society, ou_persistent13              

内容説明

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キーワード: Nitric oxide; P450 enzymes; Hydride transfer; Fusarium oxysporum; Heme-thiolate catalysis
 要旨: The mechanism of the heme-thiolate-dependent NADH-NO reductase (P450NOR) from Fusarium oxysporum was investigated by kinetic isotope effects including protio, [4S-2H]-, [4R-2H]-, [4,42H2]-NADH and stopped-flow measurements. The respective kinetic isotope effects were measured at high NO concentrations and were found to be 1.7, 2.3 and 3.8 indicating a rate-limitation at the reduction step and a moderate stereoselectivity in binding of the cofactor NADH. In a different approach the kinetic isotope effects were determined directly for the reaction of the FeIII–NO complex with [4R-2H]- and [4S-2H]-NADH by stopped-flow spectroscopy. The resulting isotope effects were 2.7±0.4 for the R-form and 1.1±0.1 for the S-form. In addition the 444 nm intermediate could be chemically generated by addition of an ethanolic borohydride solution to the ferric–NO complex at -10°C. In pulse radiolysis experiments a similar absorbing species could be observed when hydroxylamine radicals were generated in the presence of Fe (III) P450NOR. Based on these results we postulate hydride transfer from NADH to the ferric P450–NO complex resulting in a ferric hydroxylamine-radical or ferryl hydroxylamine-complex and this step, as indicated by the kinetic isotope effects, to be rate-limiting at high concentrations of NO. However, at low concentrations of NO the decay of the 444 nm species becomes the rate-limiting step as envisaged by stopped-flow and optical kinetic measurements in a system in which NO was continuously generated. The last step in the catalytic cycle may proceed by a direct addition of the NO radical to the Fe–hydroxylamine complex or by electron transfer from the NO radical to the ferric–thiyl moiety in analogy to the postulated mechanisms of prostacyclin and thromboxane biosynthesis by the corresponding P450 enzymes. The latter process of electron transfer could then constitute a common step in all heme-thiolate catalyzed reactions.

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言語: eng - English
 日付: 2001-11-20
 出版の状態: 出版
 ページ: -
 出版情報: -
 目次: -
 査読: -
 識別子（DOI, ISBNなど）: eDoc: 27109
 学位: -

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出版物 1

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出版物名: Journal of Inorganic Biochemistry
種別: 学術雑誌
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出版社, 出版地: -
ページ: - 巻号: 88 (3 - 4) 通巻号: - 開始・終了ページ: 343 - 352 識別子（ISBN, ISSN, DOIなど）: -