Purification and characterization of a cathepsin inhibitor from catfish (Pangasius sp.) of Indonesian water

Cathepsin inhibitor has been purified to homogeneity from catfish muscle (Pangasius sp.). The purification was carried out through ammonium sulphate precipitation, followed by ion exchange chromatography using DEAE-Sephadex A-75, followed by gel filtration on Sephadex G-100. Throughout the purification procedure, cathepsin inhibitory activity was determined against hemoglobin. A single band of molecular weight 16.65 kDa was obtained after the Sephadex G-100 filtration and revealed inhibitory activity against cathepsin as estimated by SDS-PAGE. The purified inhibitor possessed a specific activity of 16.9-fold higher than the initial activity with a 1.85 % yield. The optimum pH of the inhibitor was eight at 40°C. The inhibitor was stable at 10-50°C and at pH 7-9. Ions Mn^2+ increased the inhibitory activity, while Ca^2+ and Co^2+ were slightly repressed. The enzyme inhibitor extracted from this study had similar properties to available commercial inhibitors.