Catalytic properties of human platelet 12-lipoxygenase as compared with the enzymes of other origins

Abstract

Arachiidonate 12-lipoxygenase of porcine and bovine leukocytes were different in substrate specificity and immunogenicity from the enzyme of bovine platelets (Arch. Biochem. Biophys. (1988) 266, 613). In order to extend the comparative studies on the two types of 12-lipoxygenase, we purified the enzyme from the cytosol of human platelets by immunoaffinity chromatography to a specific activity of about 0.3 μmol/min per mg protein at 37°C. The purified enzyme was active with eicosapolyenoic acids and docosahexaenoic acid. Linoleic and linolenic acids were poor substrates in contrast to the high reactivity of the leukocyte enzymes with these octadecapolyenoic acids. The finding that the human platelets enzyme catalyzed 15-oxygenation of 5S-hydroxy-6,8,11,14-eicosatetraenoic acid, raised a question if lipoxins were produced by incubation of the enzyme with leukotriene A 4. Howeverm the leukogtriene A 4 was scarcely transformed to lipoxin isomers by 12-lipoxygenases of human and bvvine platelets. In sharp contrast, the porcine and bovine leukocyte enzymes converted leukotriene A 4 to various lipoxin isomers by the reaction rates of 3% and 2% of the arachidonate 12-oxygenation. Thus, 12-lipoxygenase of human and bovine platelets were catalytically distinct from the porcine and bovine leukocyte enzymes in terms of their reactivities not only with linoleic and linolenic acids, but also with leukotriene A 4 as lipoxin precursor.