Binding of human pancreatic carboxylic ester hydrolase to lipid interfaces

Human pancreatic carboxylic ester hydrolase (EC 3.1.1.1), usually characterized by its activity on water-soluble substrates, is shown to catalyze reactions taking place at a lipid/water interface. The inhibition of tributyrin hydrolysis by 1-alcohols follows the pattern of a Langmuir adsorption isotherm. Experiments performed with siliconized glass beads show that human pancreatic carboxylic ester hydrolase is adsorbed on this artificial (or substitute) interface with a dissociation constant for the enzyme-glass beads complex equal to 1.5 . 10(-8) M. The average molecular area at saturation is 4375 A2. Tripropionin hydrolysis is increased by the presence of glass beads. These results are strong arguments in favor of the interfacial activity of pancreatic carboxylic ester hydrolase. The activation of the enzyme bound to the interface is very weak. Bile salts do not prevent the adsorption of carboxylic ester hydrolase on siliconized glass beads and increase strongly the hydrolysis rate of emulsified tributyrin.