Action of phospholipase A at interfaces.

The heterogeneous catalysis of pancreatic phospholipase A (EC 3.1.1.4) is studied by kinetics on monomolecular layers of short chain phospholipids. Under certain conditions long induction times are observed experimentally which can be related with a slow reversible penetration of the enzyme into the monolayer. The influence of surface pressure, pH, sodium chloride, and Ca2f ions on this penetration step is reported. Based on a proposed two-dimensional Michaelis model, steady state and presteady state equations are derived and together with computer analysis show a good fit with the experimental results. A quantitative comparison between enzyme kinetics obtained by monolayer and bulk techniques is attempted using a common definition of the “quality” of the lipid-water interface. Possible implications of the concept of a penetration site on the enzyme are discussed.