[Characteristics of nuclear endo-DNAase from rat liver by molecular mass and cationic dependence].

Study of the isoenzymatic spectrum of nuclear DNase from rat liver demonstrated that the extracts obtained in the presence of the protease inhibitor, PMSF, contained four polypeptides with molecular masses of 120, 54, 31 and 28 kDa possessing the endo-DNase activity. Long-term storage at -20 degrees C and autodigestion of the nuclei revealed the presence of additional polypeptides with a lower molecular mass and possessing an endo-DNase activity. Treatment of rat liver nuclear extracts with trypsin caused the appearance of an active polypeptide (M(r) 145 kDa). This finding and the multiplicity of endo-DNases of different molecular masses suggest the existence of a precursor possessing a much higher molecular mass. Chromatographic separation of endo-DNases on Sephacryl S-300 revealed three fractions of 400 and more kDa possessing a Ca2+/Mg(2+)-dependent activity, however, only after trypsin treatment.