Purification and characterization of a deoxy-ribonuclease acting on native and UV irradiated DNA from young and aging rat brain.

A deoxyribonuclease has been purified to electrophoretic homogeneity from young and old rat brain. The enzyme is an endonuclease, with an optimum pH 5.0. Divalent cations are not needed for the activity. The DNase showed highest activity towards Native DNA either as such or UV irradiated with little activity on denatured DNA, apurinic DNA or DNA pretreated with mitomycin C or actinomycin D. The enzyme hydrolyzes double stranded poly (dA-dT).(dA-dT) but not other homologous or heterologous synthetic polynucleotides. The enzyme does not excise pyrimidine dimers preferentially but acts at a site away from the dimer. The DNase was partially purified from nuclei also and both the nuclear and extra nuclear enzymes showed similar properties. The specific activity of brain DNase decreases markedly with age. DNase preparations from both young and old rats showed similar apparent molecular weight (62KD) and many other properties like elution profiles and the N-terminal amino acid. However the old enzyme was more susceptible to temperature and proteolytic digestion. These results are taken to indicate a possible role for this enzyme in recognizing conformational distortions in DNA and that altered molecules of this enzyme accumulate in aging brain.