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Manganese lipoxygenase oxidizes bis-allylic hydroperoxides and octadecenoic acids by different mechanisms
Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
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2011 (English)In: Biochimica et Biophysica Acta - Molecular and Cell Biology of Lipids, ISSN 1388-1981, E-ISSN 1388-1918, Vol. 1811, no 3, 138-147 p.Article in journal (Refereed) Published
Abstract [en]

Manganese lipoxygenase (MnLOX) oxidizes (11R)-hydroperoxylinolenic acid (11R-HpOTrE) to a peroxyl radical. Our aim was to compare the enzymatic oxidation of 11R-HpOTrE and octadecenoic acids with LOO-H and allylic C-H bond dissociation enthalpies of similar to 88 and similar to 87 kcal/mol. Mn(III)LOX oxidized (11Z)-, (12Z)-, and (13Z)-18:1 to hydroperoxides with R configuration, but this occurred at insignificant rates (<1%) compared to 11R-HpOTrE. We next examined whether transitional metals could mimic this oxidation. Ce(4+) and Mn(3+) transformed 11R-HpOTrE to hydroperoxides at C-9 and C-13 via oxidation to a peroxyl radical at C-11, whereas Fe(3+) was a poor catalyst. Our results suggest that MnLOX oxidizes bis-allylic hydroperoxides to peroxyl radicals in analogy with Ce(4+) and Mn(3+). The enzymatic oxidation likely occurs by proton-coupled electron transfer of the electron from the hydroperoxide anion to Mn(III) and H(+) to the catalytic base, Mn(III) OH(-). Hydroperoxides abolish the kinetic lag times of MnLOX and FeLOX by oxidation of their metal centers, but 11R-HpOTrE was isomerized by MnLOX to (13R)-hydroperoxy-(9Z,11E,15Z)-octadecatrienoic acid (13R-HpOTrE) with a kinetic lag time. This lag time could be explained by two competing transformations, dehydration of 11R-HpOTrE to 11-ketolinolenic acid and oxidation of 11R-HpOTrE to peroxyl radical; the reaction rate then increases as 13R-HpOTrE oxidizes MnLOX with subsequent formation of two epoxyalcohols. We conclude that oxidation of octadecenoic acids and bis-allylic hydroperoxides occurs by different mechanisms, which likely reflect the nature of the hydrogen bonds, steric factors, and the redox potential of the Mn(III) center.

Place, publisher, year, edition, pages
2011. Vol. 1811, no 3, 138-147 p.
Keyword [en]
Proton coupled electron transfer, Fatty acid oxidation, PGH synthase, Mass spectrometry, Redox chemistry
National Category
Biological Sciences
URN: urn:nbn:se:su:diva-69452DOI: 10.1016/j.bbalip.2010.12.002ISI: 000289270200003OAI: diva2:477556
authorCount :5Available from: 2012-01-13 Created: 2012-01-12 Last updated: 2012-01-13Bibliographically approved

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Sahlin, Margareta
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Department of Molecular Biology and Functional Genomics
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