Metabolism of leukotrienes by L-gamma-glutamyl-transpeptidase and dipeptidase from human polymorphonuclear granulocytes.

Stimulation of human polymorphonuclear granulocytes with the calcium-ionophore A23187 and opsonized zymosan leads to the release of leukotrienes. The cell-free supernatants of the stimulated cells revealed gamma-glutamyl-transpeptidase and dipeptidase activity which induced the metabolism of exogeneously added LTC4 and LTD4 respectively. No glutathione-S-transferase activity was present in the supernatant. In the absence of calcium, no leukotrienes were generated; dipeptidase activity was slowly released and gamma-glutamyl-transpeptidase activity was not detected. By subcellular fractionation, glutathione-S-transferase activity was present in the microsomal and cytosol fractions, and gamma-glutamyl-transpeptidase and dipeptidase were recovered from the granular and microsomal fractions. By equilibrium density-gradient centrifugation, highest dipeptidase activity eluted in the range between 1.18 and 1.22 g/ml; gamma-glutamyl-transpeptidase was present in the range from 1.13 to 1.18 g/ml and 1.20 to 1.22 g/ml; glutathione-S-transferase did not enter the gradient under these conditions. Solubilization of the 100,000 g pellet of homogenized cells with Triton X-100 led to the release of soluble gamma-glutamyl-transpeptidase and dipeptidase enzymes into the supernatant.