Separation and partial characterization of four cysteine proteinases from a human epidermal cell line

Four different cysteine proteinases from a cultured human epidermal cell line (NCTC 2544) were partially purified and characterized. The biggest hydrolase was an endoaminopeptidase with the molecular weight of several hundred kilodaltons. It was a glycoprotein and had an almost neutral pH optimum. The three other hydrolases resembled lysosomal cathepsins B, H, and L in various respects except for somewhat higher molecular weight for cathepsin B (29 kDa) and the cathepsin H-like (70 kDa) hydrolase than those reported from most other tissues. Low molecular weight cysteine proteinase inhibitors ACPI (cystatin A) and NCPI (cystatin B) inhibited the cathepsins, but not the high molecular weight proteinase.