Comparative studies on the leukotriene D4-metabolizing enzyme of different types of leukocytes.

1. The leukotriene (LT) D4-metabolizing enzyme which catalyzes the conversion of LTD4 to LTE4, was investigated in various types of leukocytes from guinea pigs and humans. 2. In guinea pigs, the enzyme activity was present in macrophages but was hardly present in neutrophils, lymphocytes and eosinophils. 3. In humans, neutrophils, lymphocytes and macrophages all possessed the enzyme activity. However, enzyme activity varied with cell types and macrophages showed the highest enzyme activity among the leukocytes. 4. The subcellular localization of the LTD4-metabolizing enzyme was studied and leukocytes were divided into two groups: one which has the enzyme activity exclusively on the cell surface and the other which has the activity both on the cell surface and in the granules of leukocytes. 5. The enzyme activity was remarkably inhibited by o-phenanthroline and dithiothreitol and the inactivated enzyme was considerably reactivated by Co2+ and Zn2+, suggesting that the LTD4-metabolizing enzyme of leukocytes is a metalloenzyme.