Purification and some properties of a latent form cathepsin L from mackerel white muscle

A latent form cysteine protease was purified from the white muscle of common mackerel Scomber japonicus by ammonium sulfate fractionation and successive column chromatography. The final preparation appeared to be homogeneous on polyacrylamide gel electrophoresis. The molecular mass of the latent form was estimated to be 65 kDa by gel filtration and 69 kDa by SDS-PAGE. The latent form enzyme was activated by acid treatment or pepsin treatment, and hydrolyzed Z-Phe-Arg-MCA, hemoglobin and azocasein. The active form enzyme after acid treatment was enhanced by sulfhydryl compounds, such as dithiothreitol and cysteine, strongly inactivated by leupeptin and E-64. Consequently, we concluded that the active form cysteine protease corresponded to cathepsin L.