Proteinase inhibitors confine the activity of proteolytic enzymes of inflammatory cells, but fail to protect substrates in the immediate pericellular zone. We report quantitative imaging that demonstrates discrete, evanescent, quantized proteolytic events attributable to the release of single azurophil granules from neutrophils. The images provide information about the dynamics of this nonequilibrium system, which is characterized by overwhelmingly high local concentrations of enzymes that rapidly dissipate. With physiologic concentrations of extracellular human leukocyte elastase inhibitors (32.8 microM), the radii of the unit proteolytic events are 1.32 microm (approximately 8 times the radius of the azurophil granule) and are inversely and nonlinearly related to the concentration of proteinase inhibitor that is present in the bathing medium. We have obtained identical results with alpha1-antitrypsin, alpha2m, recombinant secretory leukocyte proteinase inhibitor, and ICI 200,355, and we have found that phagocyte-derived oxidants are not required for the genesis of this catalytic activity. Our results reveal that the enzyme:inhibitor ratio is the primary delimiter of quantized proteolysis in the local microenvironment.

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