Studies on the leukotriene D4-metabolizing enzyme of rat leukocytes, which catalyzes the conversion of leukotriene D4 to leukotriene E4.
Leukotriene D4-metabolizing enzyme was studied using rat neutrophils, lymphocytes and macrophages. These leukocyte sonicates converted leukotriene D4 to leukotriene E4. However, the leukotriene D4-metabolizing activity varied with cell type, and macrophages showed the highest activity among these leukocytes. The subcellular localization of the leukotriene D4-metabolizing enzyme of macrophages was examined, and the leukotriene D4-metabolizing activity was found to be present in the membrane fraction, but not in the nuclear, granular and cytosol fractions. When macrophages were modified chemically with diazotized sulfanilic acid, a poorly permeant reagent which inactivates cell-surface enzymes selectively, the leukotriene D4-metabolizing activity of macrophages decreased significantly (about 95%) without any inhibition of marker enzymes of microsome, cytosol, lysosome and mitochondria. When neutrophils and lymphocytes were modified with diazotized sulfanilic acid, the leukotriene D4-metabolizing activity was also inhibited about 90% by the modification. Among various enzyme inhibitors used, o-phenanthroline, a metal chelator, remarkably inhibited the leukotriene D4-metabolizing activity of leukocytes, and the o-phenanthroline-inactivated enzyme activity was fully reactivated by Co2+ and Zn2+. These findings seem to indicate that rat neutrophils, lymphocytes and macrophages possess the leukotriene D4-metabolizing metalloenzyme which converts leukotriene D4 to leukotriene E4, on the cell surface, although macrophages have a higher enzyme activity than the other two.
Nagaoka
I
I
Department of Physiological Chemistry, School of Medicine, Juntendo University, Tokyo, Japan.
Yamashita
T
T
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D004150:Dipeptidases / Q000378:metabolism*; D006168:Guinea Pigs; D007962:Leukocytes / Q000201:enzymology*; D017999:Leukotriene E4; D008264:Macrophages / Q000201:enzymology; D051381:Rats; D011919:Rats, Inbred Strains; D013189:SRS-A / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000378:metabolism*; D013347:Subcellular Fractions / Q000201:enzymology
D013189:SRS-A; D017999:Leukotriene E4; D004150:Dipeptidases; C036942:leukotriene D4 dipeptidase