Studies on the Neutral Deoxyribonuclease Activity in Highly Purified Acid Deoxyribonuclease

Abstract The presence of neutral deoxyribonuclease activity in highly purified preparation of acid deoxyribonuclease from sheep spleen (deoxyribonuclease II, EC 3.1.4.6) is described. The activity at pH 7.0 differs from the activity at pH 4.5 in its optimal ionic strength, its inhibition by tRNA, inhibition by EDTA, and activation by divalent cations. The deoxyribonuclease activity at neutral pH is not due to contamination by deoxyribonuclease I (EC 3.1.4.5) as judged from the differences between the various divalent cations activation curves, the inhibition by tRNA, and the inhibition of deoxyribonuclease I and II by purified deoxyribonuclease I inhibitor. While deoxyribonuclease I was completely inhibited by the inhibitor, deoxyribonuclease II was not inhibited at all either when assayed at pH 4.5 or at pH 7.0. Furthermore, we have shown that pH, ionic strength, and requirements for divalent cations are interdependent variables. The higher the pH at which deoxyribonuclease II is assayed, the lower its requirements for ionic strength, while its requirements for divalent cations are increased. It is highly probable that the neutral and acid deoxyribonuclease activities in our highly purified preparation of splenic deoxyribonuclease II are due to the same protein molecule.