Product activation of pancreatic lipase. Lipolytic enzymes as probes for lipid/water interfaces

During the action of pancreatic lipase and colipase on racemic 1,2-didodecanoylglycerol monolayers in the absence of bile salts, biphasic kinetics was observed under conditions of high lipid packing. Similar kinetics has earlier been reported using phospholipid-emulsified triolein droplets. These kinetics are characterized by a lag time τ(d), dependent on products accumulation at the substrate/water interface. This lag time is differentiated from the previously described enzyme concentration independent lag time τ(i) in systems of low lipid packing. Both τ(i) and τ(d) reflect a rate-limiting step due to the slow enzyme penetration into the substrate interface. The variation of τ(d) under different conditions (change in pH and concentration of Ca²⁺, enzyme, bovine serum albumin, and lipolytic products) lead us to propose a model for the product activation during lipolysis. We will discuss the use of the pancreatic lipase-colipase system to probe the lipid packing of emulsified triglyceride particles and lipoproteins using τ(d) as a reference value.