Identification of calcium-dependent proteolytic activity in human polymorphonuclear leukocytes.

Calcium-dependent proteolytic activity has been identified in extracts of human polymorphonuclear leukocytes. The activity is most pronounced in the neutral pH range with a pH optimum of 7.3. Maximal activation of the protease occurs at a free calcium concentration of 190 microM; it is half maximal at 91 microM. This protease activity is strongly inhibited by aprotinin and phenylmethylsulfonyl fluoride (PMSF) and more weakly inhibited by antipain, leupeptin, and o-phenanthroline. The protease is not activated by calmodulin nor is it inhibited by the calmodulin antagonist trifluoperazine. Gel filtration suggests a molecular weight of 74,100 daltons.