Release and Functional Characterization of the Leukotriene D4-Metabolizing Enzyme (Dipeptidase) from Human Polymorphonuclear Leucocytes

1365-3083

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Polymorphonuclear leucocytes released LTD4-dipeptidase activity in a time-, calcium-, and cell number-dependent fashion. The LTD4-dipeptidase released from polymorphonuclear leucocytes (PMN) by incubation with calcium (0.91 mm) was detectable up to a cell concentration of 1 × 106/ml and increased with higher concentrations. Maximal LTD4-dipeptidase activity within the extracellular environment was detected after 15 min of incubation (2x107/ml) in the presence of 2–4.5 mm calcium or after 30 min, when stimulation was carried out with 0.91 mm calcium. The activity of the released LTD4-dipeptidase was modulated by various metal ions and other compounds. The addition of Mn2+ Co2+, and Zn2+ (final concentration 1 mm) enhanced the LTD4-dipeptidase activity, while Cu2+ led to a complete inhibition. In the absence of exogenoas calcium EDTA inhibited LTD4-dipeptidase. Calcium up to a concentration of 5 and 10mm decreased the dipeptidase activity. The LTD4-dipeptidase is not affected by bestatin, leupeptin. or N-ethyl-maleinimide (NEM). The Km of LTD4-dipeptidase for LTD4 was 0.95±0.2μm and vmax was 737.5±112.5 pmol/min × mg protein (n = 3±SEM). The highest LTD4dipeptidase activity was obtained at physiological pH values. LTD4-dipeptidase activity can also be released from other cell types, but the enzyme activity from human PMN exceeded that of other cells (e.g. human lymphocytes/monocytes and basophils (LMB) and human lung cell suspension).

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