Studies on phospholipase A and its zymogen from porcine pancreas: I. The complete amino acid sequence

Abstract

Phospholipase A from porcine pancreas was subjected to digestion with trypsin after sulfitolysis. The resulting peptides were purified by a combination of Sephadex filtration, electrophoresis and chromatography on paper. The amino acid sequence of these peptides was determined by Edman degradation and, occasionally, hydrolysis with carboxypeptidases A and B. Alignment of the tryptic peptides into a single chain containing 123 amino acids was determined from larger overlap peptides. Some of these peptides were obtained from tryptic digests of sulfitolyzed phospholipase A after amidination of the lysine residues. Additional peptides, utilized for the correct positioning of the tryptic peptides, were obtained from cyanogen bromide fragments before and after chymotryptic digestion. Finally, confirmatory evidence for the proposed arrangement was provided by digestion of the sulfitolyzed enzyme with thermolysin. These results, along with the known sequence of the activation peptide, attached at the N-terminal end of phospholipase A, also provide the amino acid sequence of the zymogen.