Three neutral proteinases (EC 3.4.-.-) and cathepsin D have been identified in human epidermis utilizing a highly sensitive radioactive method. The proteinases were extracted in 1.0 M KCl and 0.1% Triton X-100 and separated by Sephadex G-75 chromatography. The neutral proteinase peaks were all inhibited by diisopropyl fluorophosphate and thus were serine proteinases. Incubation of the enzyme fractions with [3H]diisopropyl fluorophosphate followed by sodium dodecyl sulfate polyacrylamide gel electrophoresis demonstrated that the two larger molecular weight proteinases were enzyme mixtures. The small molecular weight [3H]diisopropyl fluorophosphate proteinase migrated as a single band. Injection of the small molecular weight neutral proteinase into rabbit skin produced a polymorphonuclear leukocyte infiltration and edema. The reaction was not observed with the diisopropyl fluorophosphate-inhibited enzyme fraction. The release of neutral proteinases may be one of the signal events in the epidermal inflammatory response.
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