| Summary: | Pig pancreatic carboxylester lipase (cholesterol esterase, E.C. 3.1.1.13) was inactivated at a tributyrin/water interface. The apparent rate constant for inactivation increased with increase in the particle surface area of the tributyrin emulsion. The large energy of activation and entropy change for inactivation (33.7 Kcal.mol-1 and 35.8 cal.mol-1.deg-1, using 5 mM sonicated tributyrin at 37 degrees C, respectively) suggest that the observed inactivation reflects denaturation of the enzyme at the tributyrin/water interface. Bile salts protected the enzyme from irreversible inactivation at the tributyrin/water interface. The protection by bile salts was related both to their concentration and to the tributyrin concentration (substrate surface area). The protection by bile salts was not related to their concentration below or above their critical micellar concentration; the binding of bile salts to enzyme was probably the dominant protection factor. Similar stabilization was observed with other detergents such as Brij-35, Triton X-100, and sodium dodecyl sulfate. These results suggest that inactivation of carboxylester lipase occurs at a high-energy lipid-water interface and that an important role of bile salts in vivo is to stabilize carboxylester lipase at interfaces.
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