MAMMALIAN collagenase is a proteolytic enzyme which specifically cleaves native triple helical collagen at physiological pH and temperature. As with other extracellular proteases, there is increasing evidence that this enzyme can be found in an inactive, latent form which may represent a proenzyme or an enzyme-inhibitor complex1-8. It has been known for some time that, like the zymogen forms of the pancreatic proteases, latent collagenase could be activated with low concentrations of trypsin2-5. The existence of inactive mammalian collagenase has been perplexing because this is often the major state in which the enzyme is found: it has not been known whether trypsin activation of latent collagenase has any physiological significance. Drawing parallels to the physiological activation of pancreatic chymotrypsinogen, procarboxypeptidase and proelastase by pancreatic trypsin, several investigators have suggested the existence of protease(s) that can activate latent collagenase in the physiological conditions in which collagenase functions 1-3. The study reported here validates this concept by demonstrating that a single cell type, the alveolar macrophage, secretes an inactive form of collagenase that can be activated in physiological conditions by a protease secreted at the same time by the same cell type.
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