Abstract
Arachidonate 12-lipoxygenase is a dioxygenase which incorporates one molecule of oxygen into arachidonic acid and produces 12S-hydroperoxy-5, 8, 10, 14-eicosate-traenoic acid. The enzyme has been found in various tissues of many animal species. Two types of 12-lipoxygenase are distinguishable in terms of substrate specificity. The leukocyte-type enzyme is active not only with arachidonic acid and other C_<20> acids but also with C_<18> acids such as linoleic and linolenic acids. In contrast, the platelet-type enzyme is almost inactive with C_<18> acids. The two enzymes are also distinct in terms of immunogenicity, heat stability and reaction time course. Furthermore, the cDNAs for porcine leukocyte and human platelet 12-lipoxygenases do not cross-hybridize each other. The substrate specificity, immunogenicity, primary structure and genomic organization of porcine leukocyte 12-lipoxygenase are closer to those of rabbit reticulocyte 15-lipoxygenase than those of human platelet 12-lipoxygenase. The leukocyte-type enzyme has also been found in porcine pituitary, bovine trachea, canine brain, and human adrenal glomerulosa cells, but the platelet type enzyme has so far been found only in platelets of several animal species.
