Purification, Characterization, and Amino Acid Sequencing of DNase γ from Rat Spleen

An endonuclease named DNase γ was purified to apparent homogeneity from rat splenocyte nuclei and its properties were characterized. We also determined the NH2-terminal and partial amino acid sequences of the proteolytic internal peptides. The molecular mass of γ DNase was 33,000 daltons as determined by SDS–polyacrylamide gel electrophoresis. A native molecular mass of 30,000 was estimated by gel filtration. Purified DNase γ is active in the presence of both Ca2+and Mg2+or Mn2+alone and inhibited by Co2+, Ni2+, Cu2+, and especially Zn2+. Maximal activity was achieved at pH 7.2 in Mops–NaOH buffer. The sequence data on the NH2-terminal and seven internal peptides obtained by sequential digestions withAchromobacterprotease I and endoproteinase Asp-N revealed that DNase γ is a novel endonuclease that shows sequence homology with DNase I.