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Journal of Lipid Research, Vol. 48, 855-862, April 2007
Copyright © 2007 by American Society for Biochemistry and Molecular Biology

Intramolecular rearrangement of linolenate peroxyl radicals in lipoxygenase reactions at lower oxygen content

Tokuko Takajo^*, Kazunori Tsuchida^*, Tsuyoshi Murahashi^*, Koichi Ueno and Ichiro Koshiishi^1,*

^* Nihon Pharmaceutical University, 10281 Komuro, Ina-machi, Kita-Adachi-gun, Saitama, 362-0806 Japan
Graduate School of Pharmaceutical Sciences, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba 260-8675, Japan

Published, JLR Papers in Press, January 16, 2007.

¹ To whom correspondence should be addressed. e-mail: ikoshi{at}nichiyaku.ac.jp

Variation of tissue oxygen content is thought to be a possible factor in determining the structural diversity of hydroperoxy fatty acids. In the present study, we evaluated the structural diversity of intermediate carbon-centered radicals at lower oxygen content. When the buffered solution (pH 7.4) containing 1.0 mM -linolenic acid, 1.0 µM soybean 15-lipoxygenase, and 1.0 mM nitroxyl radical [3-carbamoyl-2,2,5,5-tetramethyl-3-pyrroline-N-oxyl (CmP)], which selectively traps carbon-centered radicals, was incubated in a sealed vial, the generation of linolenate hydroperoxide was completed within 1 min. In the subsequent reaction at lower oxygen content, the production of the [LnA–H+O₂]·-CmP adduct was ascertained by liquid chromatography tandem mass spectrometry with precursor ion scanning. Furthermore, HPLC analysis with photodiode array detection showed that the adduct exhibits an absorption maximum at 278 nm, indicating a conjugated triene moiety. On the basis of these facts, the structure of the adduct was speculated to be C₂H₅–CH(CmP)–CH = CH–CH = CH–CH = CH–CH(OOH) –C₇H₁₄–COOH. We proposed a possible reaction pathway as follows: a linolenate 9-peroxyl radical generated in the lipoxygenase reaction might be converted into C₂H₅–·CH–CH = CH–CH = CH–CH = CH–CH(OOH) –C₇H₁₄–COOH through an intramolecular rearrangement. This intermediate radical may give rise to hydroperoxy fatty acids with structural diversity.

Supplementary key words carbon-centered radical • spin-trapping • mass spectrometry • precursor ion scanning

Abbreviations: CmP, 3-carbamoyl-2,2,5,5-tetramethyl-3-pyrroline-N-oxyl; LC, liquid chromatography; MS/MS, tandem mass spectrometry; PIS, precursor ion scanning; UV, ultraviolet

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