Further characterization of cysteine proteinase inhibitors purified from rat and human epidermis.

Cysteine proteinase inhibitors isolated from rat and human epidermis were purified to homogeneity and had isoelectric points of pH 4.31 and pH 5.10, respectively, Both inhibitors caused noncompetitive inhibition to the same degree against papain (EC 3.4.22.2), but the activity of human inhibitor against rat liver cathepsins B (EC 3.4.22.1), H (EC 3.4.22.16), and L (EC 3.422.-) was more effective than that of rat inhibitor. Dependency on pH was observed with rat inhibitor for cathepsins B and H, and with human inhibitor for cathepsin L. The reaction of the inhibitors with papain and cathepsins H and L occurred immediately, while the inhibition reaction of cathepsin B increased progressively during a preincubation time up to 40 min. Incubation at pH 7.0 maximized the progressive inhibitory activity. These findings demonstrate that cysteine proteinase inhibitors from rat and human epidermis inhibited a variety of cysteine proteinases. However, the inhibitor and enzyme interaction depends upon the enzyme, inhibitor source, and experimental conditions such as pH and preincubation time.