Cathepsin L

Cathepsin L is a lysosomal cysteine protease expressed in most eukaryotic cells. Cathepsin L is known to hydrolyze a number of proteins, including the proform of urokinasetype plasminogen activator, which is activated by Cathepsin L cleavage. Cathepsin L has also been shown to proteolytically inactivate α1 anti trypsin and secretory leucoprotease inhibitor, two major protease inhibitors of the respiratory tract. These observations, combined with the demonstration of increased Cathepsin L activity in the epithelial lining fluid of the lungs of emphysema patients, have led to the suggestion that the enzyme may be involved in the progression of this disease. Cathepsin L has also been identified as a major excreted protein of transformed fibroblasts, indicating the enzyme could be involved in malignant tumor growth. Human Cathepsin L activity is greatest under mildly acidic conditions, from pH 4.5 to 6.5. The stability of the enzyme decreases at higher pH values.