IDENTIFICATION OF RADICAL ADDUCTS FORMED IN THE REACTIONS OF UNSATURATED FATTY-ACIDS WITH SOYBEAN LIPOXYGENASE USING CONTINUOUS-FLOW FAST-ATOM-BOMBARDMENT WITH TANDEM MASS-SPECTROMETRY

Structures of alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN) r adical adducts formed in the reactions of soybean lipoxygenase with li noleic acid, linolenic acid, and arachidonic acid were determined usin g continuous flow fast atom bombardment (CF-FAB) combined with tandem mass spectrometry. The radical adducts of these lipoxygenase-dependent reactions were: n-octanoic acid radical, 12,13-dihydroxylinoleic acid radical, 12,13-epoxylinoleic acid radical, and n-pentyl radical from linoleic acid; n-octanoic acid radical, ethyl radical, and cis/trans a nd/or positional isomers (1- and S-pentenyl) of pentenyl radical from linolenic acid; and 14,15-epoxyarachidonic acid radical and n-pentyl r adical from arachidonic acid. Of these radical adducts, the n-octanoic acid radical from linoleic and linolenic acid, the ethyl radical from linolenic acid, and the 12,13-dihydroxylinoleic acid radical are iden tified for the first time in the reactions of soybean lipoxygenase. Th us the CF-FAB combined with tandem mass spectrometry employed here, by which both radical adducts and their fragment ions can be detected, i s shown to be a powerful tool in the structural identification of free radicals.