Isomer distribution of hydroxyoctadecadienoates (HODE) and hydroxyeicosatetraenoates (HETE) produced in the plasma oxidation mediated by peroxyl radical, peroxynitrite, hypochlorite, 15-lipoxygenase, and singlet oxygen

3-Methylenecholest-5-ene reacts with singlet oxygen to give 5α-hydroperoxy-3-methylenecholest-6-ene which, in turn, rearranges rapidly to 3β-hydroperoxy-5α,3α-( epidioxymethano )cholest-6-ene by free-radical cyclization , and 7α-hydroperoxy-3-methylenecholest-5-ene by allylic rearrangement.

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Formation of α-tocopherol hydroperoxide and α-tocopheroxyl radical: relevance for photooxidative stress in Arabidopsis

Scientific Reports ◽

10.1038/s41598-020-75634-0 ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Aditya Kumar ◽

Ankush Prasad ◽

Pavel Pospíšil

Keyword(s):

Singlet Oxygen ◽

Peroxyl Radical ◽

Higher Plants ◽

Xylenol Orange ◽

Hydrogen Abstraction ◽

Lipid Hydroperoxide ◽

Antioxidant Defense System ◽

High Light ◽

Oxidation Products ◽

Tocopheroxyl Radical

AbstractTocopherols, lipid-soluble antioxidants play a crucial role in the antioxidant defense system in higher plants. The antioxidant function of α-tocopherol has been widely studied; however, experimental data on the formation of its oxidation products is missing. In this study, we attempt to provide spectroscopic evidence on the detection of oxidation products of α-tocopherol formed by its interaction with singlet oxygen and lipid peroxyl radical. Singlet oxygen was formed using photosensitizer rose bengal and thylakoid membranes isolated from Arabidopsis thaliana. Singlet oxygen reacts with polyunsaturated fatty acid forming lipid hydroperoxide which is oxidized by ferric iron to lipid peroxyl radical. The addition of singlet oxygen to double bond carbon on the chromanol head of α-tocopherol forms α-tocopherol hydroperoxide detected using fluorescent probe swallow-tailed perylene derivative. The decomposition of α-tocopherol hydroperoxide forms α-tocopherol quinone. The hydrogen abstraction from α-tocopherol by lipid peroxyl radical forms α-tocopheroxyl radical detected by electron paramagnetic resonance. Quantification of lipid and protein hydroperoxide from the wild type and tocopherol deficient (vte1) mutant Arabidopsis leaves using a colorimetric ferrous oxidation-xylenol orange assay reveals that α-tocopherol prevents formation of both lipid and protein hydroperoxides at high light. Identification of oxidation products of α-tocopherol might contribute to a better understanding of the protective role of α-tocopherol in the prevention of oxidative damage in higher plants at high light.

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