OXYGENATION OF BIOMEMBRANES BY MAMMALIAN LIPOXYGENASES - THE ROLE OF UBIQUINONE

15-Lipoxygenase is implicated in the selective breakdown of mitochondr ia during red cell maturation by virtue of its capability of directly oxygenating phospholipids. To address the reason of the selectivity fo r mitochondria, we studied the reaction of pure rabbit 15-lipoxygenase with beef heart submitochondrial particles in vitro. This reaction is characterised by a loss of polyenoic fatty acids, the formation of ph ospholipid-bound hydroperoxy- and keto-polyenoic fatty acids, and oxid ative modification of membrane proteins. The total oxygen uptake excee ds the formation of oxygenated polyenoic fatty acids several times. Th e excessive oxygen uptake was not inhibited by 3,5-di-terr-butyl-4-hyd roxytoluene or by respiratory inhibitors, but was partly suppressed by superoxide dismutase plus catalase, salicylate, or mannitol. Pentane- extraction of the submitochondrial particles abolished the excessive o xygen uptake, whereas reconstitution with ubiquinone-50 restored it. A marked excessive oxygen uptake did not occur during the analogous rea ction with erythrocyte ghosts. it is proposed that ubiquinone-50 trigg ers the formation of hydroxyl radicals from 15-lipoxygenase-derived hy droperoxy-lipids via a Fenton-type reaction driven by ubisemiquinone r adicals. A new prooxidative function of ubiquinone in the biologically programmed degradation of mitochondria in certain types of cells is p roposed.