Stability studies on the cathepsin L proteinase of the helminth parasite, Fasciola hepatica

Fasciola hepatica, the liver fluke, secretes a cathepsin L cysteine proteinase. The enzyme is active over the pH range 5–9 and is remarkably stable at 37°C, pH 7.0, in contrast to mammalian cathepsin Ls that are active in the acidic pH range and are inactivated within 15 min at neutral pH. The liver fluke proteinase is also very tolerant of organic solvents, particularly dimethylformamide. However, it is completely inactivated by 1 mM Hg2+ and adversely affected by other heavy metals and divalent cations. Addition of glycerol and EDTA enhanced the liver fluke enzyme’s stability at 50°C, while glucose and glycerol protected the enzyme from inactivation by repeated freeze-thawing. The high stability of liver fluke cathepsin L suggests that it may have potential for use in bioindustrial applications.