Purification and properties of a gelatin-specific neutral protease from human skin

A neutral protease with a marked specificity for gelatin as a protein substrate has been purified to homogeneity from medium of human skin in serum-free explant culture. The pH optimum of this gelatinase is between 7.0 and 7.5 with little or no activity displayed below pH 5. Inhibition by EDTA, ethylene glycol bis(β-amino-ethyl ether)N,N,N',N'-tetraacetic acid (EGTA), and 1,10-phenanthroline suggests that the enzyme is a metalloendopeptidase. Calcium concentration-dependent inhibition of the enzyme by EGTA and EDTA suggests further that there is a requirement for extrinsic calcium. Indeed, removal of calcium reduces enzyme activity, and subsequent addition of calcium restores full activity. The gelatinase is not inhibited by serine protease inhibitors but is inhibited by cysteine, dithiothreitol, and β-mercaptoethanol. It is also inhibited by a macromolecular inhibitor of collagenase which has been purified from human skin fibroblasts. The apparent molecular weight of this enzyme, as determined by gel filtration is 120,000-150,000. The enzyme is a glycoprotein, as indicated by staining with periodic acid-Schiff reagent and by its affinity for lectins. Human skin gelatinase shows little or no reactivity toward common protein substrates, such as hemoglobin or casein, and does not cleave helical collagen. Two sites of cleavage in the sequence of gelatin, Gly-Ile and Gly-Leu, have been positively identified using synthetic substrates and tryptic peptides of collagen.