Purification and characterization of the Ca2+ plus Mg2+-dependent endodeoxyribonuclease from calf thymus chromatin.

Ca2+ plus Mg2+-dependent endodeoxyribonuclease was extracted from calf thymus chromatin and purified to a state free from contamination by other DNases. This DNase required both Ca2+ and Mg2+, or Mn2+ alone for its activity and the optimum pH for activity was at 6.5-7.5. No specificity for the 5'-base was observed. The molecular weight of the DNase was estimated to be about 25,000-30,000 by glycerol gradient centrifugation. Actin and antibody for pancreatic DNase (DNase I) did not inhibit the enzyme, whereas both strongly inhibited DNase I, suggesting that these two DNases are different enzymes.