Isolation and properties of prophospholipase A2 from human pancreatic juice

Human prophospholipase A2 was purified from pancreatic juice. The protein has a molecular weight of 14500 and a free N-terminal residue identified as aspartic acid (or asparagine). The amino acid composition was determined. Partial immunological identity has been obtained between human and porcine prophospholipase A2. As other phospholipases, the human enzyme requires the presence of calcium for its activity. However, the activity of human phospholipase A2 on egg yolk emulsion is partially inhibited at 0.4 mM calcium concentration, which differs from the porcine homologous enzyme. Kinetics of activation of the two zymogens (human and porcine) by 4 different trypsins (bovine, porcine and human) indicate a difference between the two zymogens only when activated by human trypsins, which suggests a marked specificity of both human trypsins for human prophospholipase.