ALKYL FREE-RADICALS FROM THE BETA-SCISSION OF FATTY-ACID ALKOXYL RADICALS AS DETECTED BY SPIN TRAPPING IN A LIPOXYGENASE SYSTEM

2-Methyl-2-nitrosopropane (tNB)-radical adducts from incubation mixtures of fatty acids and soybean lipoxygenase in borate buffer (pH 9.0) were measured by electron paramagnetic resonance (EPR). In addition to the previously reported six-line signal of secondary carbon-centered radicals (RĊHR′), a weak signal submerged in the baseline was detected after the peroxidation phase was finished. We propose that this radical is a decomposition product formed via β-scission of fatty acid alkoxyl radicals. EPR spectra of tNB-radical adducts formed in mixtures of either linoleic acid, arachidonic acid, or 15-hydroperoxyeicosatetraenoic acid with lipoxygenase exhibited hyperfine structure characteristic of tNB/·CH2CH2R with hyperfine coupling constants: aN = 17.1 G; aβH = 11.2 G (2H); and aγH = 0.6 G (2H). In the case of linolenic acid, this radical adduct showed hyperfine structure characteristic of tNB/·CH2CHCHR′ with hyperfine coupling constants: aN = 17.1 G; aβH = 10.9 G (2H); aγH = 1.1 G; and aδH = 0.5 G. In accord with the decomposition scheme of hydroperoxides derived from unsaturated fatty acids, the radical adducts tNB/·CH2CH2R and tNB/·CH2 CHz.dbnd;CH z.sbnd;R′ were assigned as the pentyl and 2-pentenyl radicals, respectively. © 1990.