Bovine pancreatic deoxyribonuclease A. Isolation, composition, and amino acid sequences of the tryptic and chymotryptic peptides.

The first phase of the determination of the primary structure of chromatographically homogeneous bovine pancreatic deoxyribonuclease A has been the isolation of 23 principal peptides from tryptic digests of the reduced and alkylated protein and 20 peptides from a chymotryptic hydrolysate. Seven of the latter series provide information on the ordering of peptides of the tryptic series. The results provide the basis for the derivation of the structural formula of DNase A from the subsequent study of the products of cyanogen bromide cleavage reported in the accompanying paper. The determinations of the sequences of the peptides have been facilitated by a scaling down of the subtractive Edman procedure to the use of 1 to 2 nmoles of peptide per step through the use of amino acid analyzers operating in that range.