Rat pancreatic phospholipase A2: purification, characterization, and N-terminal amino acid sequence

Phospholipase A2 was purified from rat pancreas by heat treatment of the homogenate and the sequential use of DEAE-Sepharose chromatography, CM-Sepharose chromatography, and reverse-phase high-performance liquid chromatography (HPLC). Prophospholipase A2 was not separated from the phospholipase A2 by CM-Sepharose chromatography under the conditions used, but it was well resolved by the reverse-phase HPLC. The enzyme was homogeneous on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and on analytical HPLC, and its molecular weight was estimated to be 14,000. The enzyme specifically hydrolyzed an acylester bond at the sn-2-position of the phospholipid examined. The purified enzyme has a pH optimum in the range of pH 9.5 to 10.5 and requires the presence of Ca2+ (3 mM) and sodium deoxycholate (0.1%) for optimum activity. The amino acid sequence of the first 32 residues in the N-terminal region of the enzyme was determined. The sequence revealed a marked homology with those of pancreatic phospholipases A2 of man, pig, ox, and horse, and porcine intestinal phospholipase A2 reported previously.