Arachidonic acid 15-lipoxygenase and airway epithelium. Biologic effects and enzyme purification

Pulmonary epithelial cells may be primarily responsible for initiating or regulating inflammatory responses in the airways, in part by releasing chemical mediators. Among the most potent mediators of inflammation are the lipoxygenase metabolites of arachidonic acid, including the leukotrienes and the other mono- and dihydroxyeicosatetraenoic acids (HETEs). The human airway epithelium contains significant 15-lipoxygenase activity. Although some biologic functions of 15-lipoxygenase metabolites are known, further understanding of the role of this enzyme in the airway requires localization in tissue and studies of expression, regulation, and biologic activity. Towards these aims, we purified and characterized 15-lipoxygenase from eosinophil-enriched leukocytes. First, we studied cofactors that may be involved in regulating enzymatic activity. We discovered that calcium and phosphatidylcholine both enhanced, but ATP inhibited, the 15-lipoxygenase activity of highly enriched enzyme. Second, we isolated to homeogeneity, for the first time, human 15-lipoxygenase. This led to the determination of the N-terminal amino acid sequence and the discovery of homology among various mammalian lipoxygenases. Further research using purified lipoxygenase is expected to increase our understanding of the biologic roles and biochemical features of 15-lipoxygenation of arachidonic acid.