In order to investigate properties of acid ribonuclease (RNase) in diethylnitrosamine (DEN)-induced rat hepatoma, the enzyme was isolated by DEAE-cellulose chromatography. Substrate specificities, optimal pH and heat inactivation of acid RNase in DEAE-cellulose peak
fractions were studied and compared with those of normal controls. Also studied were effects of divalent cations on acid RNase activities.
1) Acid RNase in normal rat liver and DEN-induced hepatoma were isolated by DEAE-cellulose chromatography into two peaks (peak I and II).
2) Substrate specificities of acid RNase in DEAE-cellulose peak I obtained from hepatoma were polyuridylate (poly U), RNA, polyadenylate (poly A) and polycytidylate (poly C) in order of decreasing activity, being greatly increased in its hydrolytic activity against poly A and decreased against poly C as compared with other DEAE-cellulose peak fractions obtained from normal rat liver and DEN-induced hepatoma.
3) The pH-activity profile of acid RNase in DEAE-cellulose peak I obtained from hepatoma shifted to alkaline pH showing its maximal activity at pH 5.5 while that from normal rat liver showed its maximal activity at at 5.0. Heat inactivation studies revealed that acid RNase in DEAE-cellulose peak I obtained from hepatoma was more resistant to heat inactivation than that from normal rat liver.
4) In the presence of Mgt+, Cat+ and Mnz+, acid RNase in DEAE-cellulose peak I obtained from normal rat liver was increased in its hydrolytic activity on various poluribonucleotides and RNA. Acid RNase activity in DEAE-cellulose peak I obtained from hepatoma was decreased in the presence of the same divalent cations when poly U, poly A or poly C was used as substrate but increased when RNA was used as substrate.
These results indicate that property of acid RNase in DEN-induced hepatoma was different from that in normal rat liver suggesting that the enzyme might play an important role in development and maintenance of DEN-induced hepatoma.
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