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.