Abstract
Two types of arachidonate 12-lipoxygenase which catalyze the transformation of arachidonic acid to 12(S)-hydroperoxy-5,8,10,14-eicosatetraenoic acid have been classified into leukocyte-type and platelet-type in terms of their substrate specificities, immunogenicities, primary structures and gene organizations. The leukocyte-type enzyme has been found not only in leukocytes but also in bovine tracheal epithelium, porcine anterior pituitary, canine brain and rat pineal gland. Recently the platelet-type enzyme was also found in tissues other than platelets. Human and mouse epidermal cells as well as human epidermoid carcinoma A431 cells contain a platelet-type enzyme. The leukocyte enzyme oxygenates not only free polyenoic acids but also more complex substrates such as phospholipids and lipoproteins. The finding that 12-lipoxygenase transforms low density lipoprotein to its oxidized form suggests the possible involvement of this enzyme in the pathogenesis of atherosclerosis. The platelet enzyme reacts with leukotriene A_4 to produce bioactive compounds, lipoxin A_4 and B_4.
