Interaction of ceruloplasmin and 5-lipoxygenase.

The interaction between ceruloplasmin (CP), the multicopper oxidase of human plasma, and 5-lipoxygenase (5-LO), the key enzyme of leukotriene synthesis, is shown for the first time. By Western-blotting and mass spectrometry of tryptic fragments, it is shown that 5-LO from protein extract of human leukocytes binds with immobilized CP. Dose-dependent influence of intact CP on leukotrienes synthesis is found: CP reduced leukotrienes synthesis in leukocytes in a dose above 50 µg/ml (normal CP concentration in plasma is about 300-400 µg/ml). Proteolyzed CP and apo-form of CP is unable to inhibit activity of 5-LO. CP increased activity of 5-LO at low doses (5-10 µg/ml). On the whole, the influence of CP on phagocytosis index of leukocytes coordinates with influence on activity of 5-LO: the index increased in the range of 2-10 µg/ml CP and decreased at doses of CP above 40 µg/ml. The dual role of CP in regulation of cellular response of leukocytes is discussed.