Studies on Prophospholipase A2 and Its Enzyme from Human Pancreatic Juice

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Abstract
Upon tryptic activation of pure human prophospholipase A2, a heptapeptide is released from the N-terminal part of the protein yielding active phospholipase A2 (EC 3.1.1.4). The kinetics of the activation process and the amino acid sequence of the activation peptide strongly resemble those of pancreatic zymogens of other mammalian sources. The kinetic properties of human phospholipase A2 and its zymogen are compared with those of the corresponding porcine enzyme using substrates present as micelles, molecular dispersed solutions or as monomolecular surface films. The most obvious difference between the human and porcine phospholipase A2 is the low enzyme activity of the former protein at pH 8.0 as compared to pH 6.0, against micellar and monomeric substrates. Neither the Ca2+ binding properties nor the inhibition kinetics of the human enzyme using haloketones can easily explain this different pH optimum. The sequence analysis of the N-terminal region of the first 40 residues is reported.