| Abstract
| - 1. Two main DNases were found in the dried liver extract of a snail, Achatina fulica. They were purified by the phosphocellulose batch method and by phosphocellulose column chro-matography. The enzyme eluted earlier from the phosphocellulose column was designated as Achatina DNase-1 and the other as Achatina DNase-2. DNase-1 was purified further by QAE-Sephadex A-25 column chromatography (twice) just before use because of the instability of the purified enzyme. By these procedures, DNase-1 and 2 were purified 200- and 130-fold, respectively. 2. Divalent or monovalent cations had no marked effect on either enzyme. They showed pH optima of 4.8 (DNase-1) and 5.2 (DNase-2). Ionic strength was found to be critical for the maximal activity. The isoelectric points of DNase-1 and 2 were both 6.9. On heating at 70-75°C for 5 min, each enzymic activity fell to half of the initial value. 3. The enzyme preparations degraded native DNA 1.5-2.5 times faster than heat-denatured DNA. They both degraded heat-denatured DNA endonucleolytically, to give oligonucleotides with 3′-phosphates. 4. The 3′-phosphoryl and 5′-hydroxy termini of the resulting oligonucleotides were analyzed. DNase-1 possessed marked specificity for dThd at 3′-termini and dAdo at 5′-termini in the early stages of degradation, but only for dAdo at 5′-termini in the later stages. DNase-2 showed some preference for purine nucleotides at both 3′- and 5′-termini in the later stages of degradation.
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