Bivalent cation and ATP requirements of endonucleases from rat liver nuclei

The distribution of different types of DNase in rat liver nuclei was determined after a purification procedure involving ion exchange chromatography and gel filtration. As major enzymes Ca2+, Mg2+-dependent endonuclease, Mn2+-dependent endonuclease and an acid endonuclease were identified, sharing 60, 20 and 10% of the total activity, respectively. Mn2+-dependent endonuclease is a novel enzyme with a molecular mass of 30 +/- 5 kilodaltons. The synergistic effect of Ca2+ and Mg2+ ions for the Mn2+-dependent enzyme was lower by an order of magnitude than that of the Ca2+ and Mg2+-dependent endonuclease. The Ca2+ and Mg2+-dependent nuclease activity represents a heterogeneous population of enzymes. One of the cation dependent enzymes (Mr 25 +/- 5 kD) is stimulated by ATP the ATP optimum being 0.1 mM and the Mg2+ requirement 1 mM. The ATP-dependent endonuclease belongs to the minor endonucleases separable from the major ones.