Hydrolysis of mixed monomolecular films of phosphatidylcholine/triacylglycerol by pancreatic phospholipase A2.

We studied the effect of glycerides on pancreatic phospholipase A2 hydrolysis of mixed monomolecular films of trioctanoylglycerol/1,2-didodecanoyl-sn-glycero-3-phosphocholine with the technique of Piéroni and Verger [(1979) J. Biol. Chem. 254, 10090-10094]. The quantity of enzyme adsorbed to the interface was concomitantly determined with [3H]amidinated phospholipase. At phospholipid packing above the critical penetration pressure, triacylglycerol stimulates phosphatidylcholine hydrolysis to a great extent. On the other hand, the activity of pancreatic phospholipase A2 on a mixed film is inhibited by the action of pancreatic lipase. Interface binding of phospholipase A2 to the lipid substrate does not imply activity.