title: Conversion of leukotriene D4 to leukotriene E4 by a dipeptidase released from the specific granule of human polymorphonuclear leucocytes.
abstract: Leukotriene D4 (LTD4), the most active spasmogenic leukotriene constituent of the slow reacting substance of anaphylaxis was converted by suspended human polymorphonuclear leucocytes (PMNs) to a single, less polar metabolite which was not further catabolized. This product was identified as leukotriene E4 (LTE4) by its retention time during reverse phase-high performance liquid chromatography (RP-HPLC) and subsequent bioassay on the guinea-pig ileum. LTD4 with a retention time of 21 +/- 1.6 min (mean +/- SD) and a contractile activity of 5.0 +/- 0.4 u./pmol (mean +/- SD) was quantitatively converted extracellularly by PMNs to LTE4 with a retention time of 26 +/- 1.8 min and a contractile activity of 1.2 +/- 0.3 u./pmol. Subcellular fractionations of PMNs revealed the recovered LTD4-to-LTE4 converting activity, termed LTD4 dipeptidase, to be localized only in he granule fraction. There was a time- and calcium-dependent extracellular release of LTD4 dipeptidase in association with lysozyme (r = 0.97, n = 16, P less than 0.001), a constituent of both specific and azurophilic granules, in the absence of release of cytoplasmic lactate dehydrogenase (LDH) and of beta-glucuronidase from the azurophilic granule. Phorbol myristate acetate (PMA), which selectively induces secretion of specific granules, released lysozyme and the LTD4 dipeptidase in a constant dose-dependent manner from PMNs (r = 0.96, n = 8, P less than 0.001). Calcium ionophore A23187 at concentrations less than 10(-7) M stimulated the parallel secretion of LTD4 dipeptidase and lysozyme (r = 0.91, n = 9, P less than 0.005), dipeptidase and lysozyme (r = 0.91, n = 9, P less than 0.005), whereas higher concentrations resulted in secretion of beta-glucuronidase and additional lysozyme without further release of dipeptidase. Thus, human PMNs can convert LTD4 to LTE4, a less vasoactive and spasmogenic leukotriene, via the secretion of a dipeptidase associated with the specific granules.
mesh_terms: D002478:Cells, Cultured; D003594:Cytoplasmic Granules / Q000201:enzymology; D004150:Dipeptidases / Q000378:metabolism*; D005966:Glucuronidase / Q000378:metabolism; D006801:Humans; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D017999:Leukotriene E4; D009113:Muramidase / Q000378:metabolism; D009504:Neutrophils / Q000201:enzymology*; D013189:SRS-A / Q000031:analogs & derivatives* / Q000378:metabolism*; D013997:Time Factors
chemical_list: D013189:SRS-A; D017999:Leukotriene E4; D007770:L-Lactate Dehydrogenase; D009113:Muramidase; D005966:Glucuronidase; D004150:Dipeptidases; C036942:leukotriene D4 dipeptidase