Bovine pancreatic deoxyribonuclease D.

Of the four deoxyribonucleases, DNases A, B, C, and D, observable by chromatography of preparations of the pancreatic enzyme on cellulose phosphate, DNase D, the component present in the smallest amount, has not been previously characterized. Peptide maps show that the sequence of the amino acid residues in the polypeptide chain of DNase D is indistinguishable from that of DNase C; analysis of the carbohydrate side chain shows that DNase D contains 1 galactose and 1 sialic acid residue not present in DNase C. With the knowledge that DNase C differs from DNase A by the substitution of 1 proline for 1 histidine residue in the sequence, and that DNase B differs from DNase A only in that it is a sialoglycoprotein, we now see that the bovine pancreas synthesizes each of two amino acid sequences with and without the addition of galactose and sialic acid to the carbohydrate side chain. In order to prepare small amounts of DNase D in stable form, traces of proteolytic activity in the samples were removed by taking advantage of the affinity of the enzyme for Cazf. On DEAE-celluloses at pH 8.0, the DNases are strongly adsorbed and can be eluted relatively specifically by increasing concentrations of Ca2+ in the eluting buffer (gradient from 0 to 2 mM Ca2+). This method of purification is applicable to DNases A, B, C, and D and provides further evidence of the marked effect of Ca2f on the properties of these enzymes.