Partial purification and characterization of histone hydrolase in ratliver lysosomes

Abstract

We found histone hydrolytic activity in rat liver lysosomes at high specific activity. The enzyme having histone hydrolytic activity was purified 26 fold from rat liver homogenate and separated from the other cathepsins in rat liver lysosomes by chromatography on DEAE-cellulose and Sephadex G-200. The partially purified enzyme has hydrolytic activities to both histone and casein. We tried to separate histone hydrolytic activity from casein hydrolytic activity by column chromatography and isoelectric focusing electrophoresis. However, we failed to separate these activities. The column chromatography profiles are similar fto histone and casein hydrolytic activities. In present enzyme histone and casein hydrolytic activities show optimum activity at pH 5.0 and pH 6.0,respectively. These activities are activated by dithiothreitol and are inhibited by iodoacetic acid and L-Leupeptin at the same extent. Histone hydrolytic activity has two isoelectric points at pH 4.09 and pH 6.04 which are exactly same as those of casein hydrolytic activity. Molecular weight of the enzyme is about 37000 by gel filtration. Judging from above results we may conclude that enzyme having both activities is a new enzyme different from other cathepsins and histone hydrolases.