The Primary Structure of Bovine Pancreatic Phospholipase A[sub2].

The complete amino acid sequence of bovine phospholipase A₂ (EC 3.1.1.4) was determined. This enzyme has a molecular weight of 13 782 and consists of a single polypeptide chain of 123 amino acids cross-linked by seven disulfide bridges. The main fragmentation of the polypeptide chain was accomplished by digesting the reduced and thialaminated derivative of the protein with trypsin, staphylococcal protease and cyanogen bromide. A number of chymotryptic peptides were used for alignment and to obtain overlaps of at least two residues. The sequence of the peptides was determined by Edman degradation by means of direct phenylthiohydantoin identification in combination with identification as dansyl amino acids. Although 71% of all residues of phospholipase A₂ from bovine, porcine and equine sources are conserved, bovine phospholipase A₂ differs from the others by the total number of residues and by substitutions at 20 (porcine) and 33 (equine) positions. [ABSTRACT FROM AUTHOR]