Deoxyribonuclease A, a Novel Deoxyribonuclease Highly Active toward Polydeoxyadenylic Acid and Polythymidylic Acid from Achatina fulica

Abstract

Two novel deoxyribonucleases, termed DNases A and A', have been purified from the hepatopancreas of Achatina fulica (agate snail). DNases A and A' were obtained in 3.6% and 7.7% yields by acetate buffer extraction and successive chromatography on hydroxyapatite, phosphocellulose and poly (A)-Sepharose. The two DNases are highly active toward poly (dA) and at a salt concentration of 0.15M and pH 5.0 exhibit 10-fold higher hydrolyzing activities toward poly (dA) than toward calf thymus denatured DNA. The enzymes also act considerably on poly (dT) at pH 4.0, but do not appreciably digest other synthetic homopolymers such as poly (dC), poly (dG) and poly (A). The limit products obtained by exhaustive digestion of poly (dA) with DNases A and A' are 98% and 99% acid-soluble and consist of oligonucleotides with an average chain length of about 5 nucleotides containing barely detectable dimers and trimers, respectively. These fragments have terminal 5'-hydroxyl and 3'-phosphate groups. The mode of action appears to be endonucleolytic. Both enzymes have the same pH optimum of 5.0 for poly(dA)hydrolyzing activity. Ionic strength is critical for the maximum activity.