An Endonuclease Associated with Bovine Plasma Albumin Fraction

A nucleolytic enzyme found in aged bovine plasma albumin Fraction V has been purified approximately 400-fold. The purified preparation hydrolyzes native or denatured deoxyribonucleic acid and ribosomal ribonucleic acid. The three activities appeared to reside in a protein. Native deoxyribonucleic acid is degraded by the enzyme at a somewhat greater rate than is denatured deoxyribonucleic acid or ribosomal ribonucleic acid, and the latter two nucleic acids are hydrolyzed at approximately the same rate. The enzyme is activated by the presence of a divalent cation (Mn2+, Mg2+, or Co2+) and requires both Co2+ (6 x 10-4 m) and Ca2+ (3 x 10-4 m) for the maximal reaction velocity. Potassium phosphate is inhibitory. The optimal pH is around 7.4 with collidine-HCl buffer, and the isoelectric point is 7.3. The molecular weight of the enzyme is approximately 38,000 as determined by gel filtration on Sephadex G-100. The action of the enzyme is predominantly endonucleolytic and the mechanism of digestion seems to be of a single hit type. The reaction products are 5'-phosphate-terminated mononucleotides and oligonucleotides, and the latter are converted largely to mononucleotides after extensive degradation.