The role of calcium ions and bile salts on the pancreatic lipase-catalyzed hydrolysis of triglyceride emulsions stabilized with lecithin.
Lecithin-stabilized triglyceride emulsions are subject to hydrolysis by pancreatic lipase. The time profiles of these reactions are characterized by a lag-phase and a zero-order phase. Lag phases are more pronounced with long-chain triglycerides. Ca2+ is effective in reducing the lag-phase and activating lipase. Kinetic analysis of the reactions suggests that, like previous findings by others, taurodeoxycholate (TDC) micellar solutions combine with the lipase-colipase complex to form another catalytically active enzyme form. This enzyme form exhibits reduced activity in the absence of Ca2+. In the presence of Ca2+ the mixed micelle-lipase complex becomes more active and opens a new pathway for lipolysis. It is suggested that this enzyme form can bind more easily to interfaces with different physicochemical properties. Under these conditions, Ca2+ activates the lipolysis of short-, medium-, and long-chain triglycerides by a similar mechanism. Maximum activities were measured in the presence of approximately 6 mM TDC and 30 mM Ca2+. The experimental conditions approximate the physiological conditions in the gastrointestinal tract since all of the factors studied here have been reported to be necessary for in vivo lipolysis and/or absorption of triglycerides. A mechanistic model for lipolysis in the presence of Ca2+ and the bile salt TDC is proposed which accounts for most of the experimental observations in a quantitative manner.
Department of Pharmaceutical Chemistry, University of Kansas, Lawrence 66045.
F J
FJ
Alvarez
V J
VJ
Stella
D001647:Bile Acids and Salts / Q000032:analysis*; D002118:Calcium / Q000032:analysis*; D002384:Catalysis; D055598:Chemical Phenomena; D002621:Chemistry; D004655:Emulsions; D005227:Fatty Acids / Q000032:analysis; D006868:Hydrolysis; D008049:Lipase / Q000378:metabolism*; D008823:Micelles; D008939:Mitotane / Q000032:analysis; D010179:Pancreas / Q000201:enzymology*; D010713:Phosphatidylcholines / Q000032:analysis*; D013657:Taurodeoxycholic Acid / Q000032:analysis; D013997:Time Factors; D014280:Triglycerides / Q000378:metabolism*
D001647:Bile Acids and Salts; D004655:Emulsions; D005227:Fatty Acids; D008823:Micelles; D010713:Phosphatidylcholines; D014280:Triglycerides; D013657:Taurodeoxycholic Acid; D008939:Mitotane; D008049:Lipase; D002118:Calcium