Regulation of carboxylester lipase adsorption to surfaces. 1. Chemical specificity

The chemical specificity of the adsorption of porcine pancreatic carboxyl ester lipase to pure lipid surfaces was examined. Adsorption of native and catalytically inactivated enzyme was measured at the argon-buffer interface by using lipid films near the point of collapse. Protein adsorbed readily to films of triolein, 1,3-diolein, methyl oleate, oleonitrile, oleyl alcohol, and 13,16-docosadienoic acid. However, recovery of enzyme activity was variable. These differences and the changes in surface pressure accompanying adsorption indicated the occurrence of enzyme denaturation at the interface. Denaturation was controlled largely by surface free energy but showed some chemical specificity at high surface pressures. Adsorption of protein to the lipids was comparable when measured under either equilibrium or initial rate conditions. Together with surface pressure changes that accompany adsorption, the data indicate a relative lack of specificity for the enzyme-surface interaction. Adsorption to 13,16-docosadienoic acid and 1,3-diolein obeyed the Langmuir adsorption isotherm. Dissociation constants ranged from 10 to 50 nM, depending on enzyme form, ionic strength, and pH. With both lipids, a monolayer of enzyme was adsorbed at saturation. In contrast to these results, adsorption of enzyme activity and protein to films of 1-palmitoyl-2-oleoyl-phosphatidylcholine was less than or equal to 5% of that observed with the other lipids under all conditions. Comparison of rate constants for adsorption to 13,16-docosadienoic and 1,3-diolein as a function of subphase pH indicated a marked dependence on the ionization state of the fatty acid. Overall, the data suggest that the presence of zwitterionic and anionic lipids may regulate the interaction of the enzyme with substrate-containing surfaces in vivo.