Interactions of serum albumin and other proteins with porcine pancreatic lipase

Abstract

Pancreatic lipase is an interfacial enzyme that binds to the oil-water interface of its emulsified triglyceride substrate. Its catalytic activity is inhibited by “hydrophobic” proteins, such as serum albumin and β-lactoglobulin. The inhibition is an effect of a competition for the interface, and lipase is shown to have a −50- to 100-fold higher affinity for the interface than these proteins, although lipase does not show hydrophobic interactions by other criteria. This indicates that the binding of lipase to its substrate may not only be based on hydrophobic interactions, but also on polar interactions which give specificity and additional strength to the binding. Bile salts compete with proteins including lipase for the substrate interface and in concentrations above the critical micellar concentration clear the interface of proteins. A specific reunion of lipase with the substrate and a restoration of catalytic activity in the presence of bile salts is affected by colipase even in the presence of high concentrations of serum albumin and β-lactoglobulin. It is postulated that an important function of bile salts in the intestinal lumen is to clear the interface of the dietary fat from proteins of exo- and endogeneous sources thus making it available for pancreatic lipolysis.