Hydrolysis of human milk fat globules by pancreatic lipase: role of colipase, phospholipase A2, and bile salts.

Human milk fat globules were used to explore how dietary triglycerides are hydrolyzed by pancreatic lipase. These triglycerides were hydrolyzed very slowly by lipase alone as if the surface layer of proteins and phospholipids impeded the action of the enzyme. The inhibition of lipase activity could be overcome by addition either of colipase or of pancreatic phospholipase A2. Colipase enhanced triglyceride hydrolysis in a dose-dependent manner whether bile salts were present or not. Bile salts had no effect on the activity of pancreatic lipase alone but further enhanced the activity at all concentrations of colipase tested. Bile salts were a prerequisite to relieve inhibition of lipase activity by phospholipase A2. Human milk fat globules exposed to phospholipase A2 should be representative of a physiological substrate for pancreatic lipase. A major new observation was that bile salts, even at high concentrations, stimulated triglyceride hydrolysis of such phospholipase-treated globules by pancreatic lipase also in the absence of colipase.