Identification of dipeptidyl peptidase III in human neutrophils

We have found activity of dipeptidyl peptidase (DPP) III, one of the most i mportant enkephalin-degrading enzymes in the central nervous system, in hum an neutrophils. HPLC analysis of the peptide fragments produced by treatmen t of leucine-enkephalin with isolated neutrophils in the presence of inhibi tors of other enkephalin-degrading enzymes revealed that the enzyme in huma n neutrophils cleaved dipeptides from the NH2 terminus of leucine-enkephali n, suggesting the presence of DPPIII activity in human neutrophils. Using a specific synthesized substrate and proteinase inhibitors, it was found tha t the neutrophils have 19.2 +/- 3.6 mu M/h/5 x 10(6) cells of beta-naphthyl amine for the enzyme. It was also confirmed that spinorphin and tynorphin, both reported to inhibit the activities of enkephalin-degrading enzymes, ha d potent inhibitory activities (IC50: 4.0 and 0.029 mu g/ml, respectively) against the enzyme. The presence of DPPIII activity in human neutrophils su ggests that the biologically active peptides which are associated with enke phalin play a physiological role in regulating enkephalin or inflammatory m echanisms in peripheral tissues. (C) 2000 Academic Press.