Apurinic DNA endonucleases from Drosophila melanogaster embryos

Apurinic DNA endonuclease activity from Drosophila melanogaster embryos was resolved into two separable forms by phosphocellulose chromatography, one which flowed through the column (Fraction I) and the other which was retained and eluted at approximately 200 mM potassium phosphate (Fraction II). Both fractions, purified further by glycerol gradient sedimentation, were found to introduce nicks into DNA that were specific for and equal in number to the alkali-labile sites in depurinated DNA. They had similar apparent Km values for apurinic sites (0.7 nM apurinic sites for Fraction I and 0.8 nM for Fraction II), but differed with respect to optimal pH, Mg++ requirement and sensitivity to EDTA.