ABSTRACT Surface pressure-molecular area curves of pure and mixed monolayers of lipolytic product... more ABSTRACT Surface pressure-molecular area curves of pure and mixed monolayers of lipolytic products (a mixture of oleic acid and 1,2-dioleoyl-sn-glycerol (OA-DO) at a 1:1 molar ratio), oleic acid (OA) and purified soybean oil (TG) spread at the argon-water interface were obtained. The results reveal that OA-TG and (OA-DO)-TG mixtures behave ideally when spread over a subphase at pH 8.0.We also determined the surface pressure-molecular area curves of lipolytic products (OA-DO) at the argon-water interface in the absence or presence of an excess of triglycerides. In the presence of an excess of TG, the films of OA-DO can be compressed up to surface pressures identical to the collapse pressure of the OA-DO when present alone. Furthermore, the fact that at the collapse pressure, the area occupied by the OA-DO mixture was the same in both the absence and presence of TG showed that under the experimental conditions used, negligible amounts of lipolytic products were dissolved in the oil and aqueous phases at both pH 5 and pH 8. The fraction of the surface occupied by OA-DO molecules varied from 80 to 100% at surface pressures ranging from 18 to 30 mN m−1.
Using the oil drop technique, we studied the effects of colipase and bile salts on the rate of hy... more Using the oil drop technique, we studied the effects of colipase and bile salts on the rate of hydrolysis of soybean oil by human pancreatic lipase (HPL) as well as on the interfacial binding. Upon continuously recording the decrease in the interfacial tension with time, a 10-15-fold increase in the HPL activity was found to occur in the presence of colipase. The catalytic rate constants of hydrolysis measured at the oil drop surface were found to be of the same order of magnitude as those obtained with monomolecular films spread at the air-water interface. Biotin-labeled HPL (HPL*) was used to determine the amount of adsorbed enzyme using an ELISA test. Less than 1% of the total amount of injected HPL* molecules was found to have adsorbed to the oil-water interface, and no significant effects of colipase on HPL* binding were observed. No significant changes in the hydrolysis rates or the binding of HPL* were detected in the presence of bile salts at concentrations ranging from below their critical micellar concentration (CMC) up to 100 microM. At the oil-water interface, in the absence or presence of bile salts below their CMC, it can be concluded that the colipase is a true lipase cofactor, i.e, it increases the enzyme turnover (approximately 10-15-fold) and does not affect the interfacial lipase adsorption.
The surface behaviour of two bile salts, sodium deoxycholate (NaDC) and sodium taurodeoxycholate ... more The surface behaviour of two bile salts, sodium deoxycholate (NaDC) and sodium taurodeoxycholate (NaTDC), as well as that of tetrahydrolipstatin (THL), a potent gastrointestinal lipase inhibitor, was studied at air/water and oil/water interfaces, using interfacial tensiometry methods. The surface behaviour of NaDC and NaTDC was comparable at both oil/water and air/water interfaces. A fairly compact interfacial monolayer of bile salts is formed well below the critical micellar concentration (CMC) and can help to explain the well-known effects of bile salts on the kinetic behaviour of pancreatic lipases. Using the Wilhelmy plate technique, the surface pressure-molecular area curves recorded with THL at the air/water interface showed a collapse point at a surface pressure of 24.5 mN.m(-1), corresponding to a molecular area of 70 A(2). Surprisingly, using the oil drop method, a limiting molecular area of 160 A(2) was found to exist at the oil/water interface. On the basis of the above data, space-filling models were proposed for bile salts and THL at air/water and oil/water interfaces.
ABSTRACT Surface pressure-molecular area curves of pure and mixed monolayers of lipolytic product... more ABSTRACT Surface pressure-molecular area curves of pure and mixed monolayers of lipolytic products (a mixture of oleic acid and 1,2-dioleoyl-sn-glycerol (OA-DO) at a 1:1 molar ratio), oleic acid (OA) and purified soybean oil (TG) spread at the argon-water interface were obtained. The results reveal that OA-TG and (OA-DO)-TG mixtures behave ideally when spread over a subphase at pH 8.0.We also determined the surface pressure-molecular area curves of lipolytic products (OA-DO) at the argon-water interface in the absence or presence of an excess of triglycerides. In the presence of an excess of TG, the films of OA-DO can be compressed up to surface pressures identical to the collapse pressure of the OA-DO when present alone. Furthermore, the fact that at the collapse pressure, the area occupied by the OA-DO mixture was the same in both the absence and presence of TG showed that under the experimental conditions used, negligible amounts of lipolytic products were dissolved in the oil and aqueous phases at both pH 5 and pH 8. The fraction of the surface occupied by OA-DO molecules varied from 80 to 100% at surface pressures ranging from 18 to 30 mN m−1.
Using the oil drop technique, we studied the effects of colipase and bile salts on the rate of hy... more Using the oil drop technique, we studied the effects of colipase and bile salts on the rate of hydrolysis of soybean oil by human pancreatic lipase (HPL) as well as on the interfacial binding. Upon continuously recording the decrease in the interfacial tension with time, a 10-15-fold increase in the HPL activity was found to occur in the presence of colipase. The catalytic rate constants of hydrolysis measured at the oil drop surface were found to be of the same order of magnitude as those obtained with monomolecular films spread at the air-water interface. Biotin-labeled HPL (HPL*) was used to determine the amount of adsorbed enzyme using an ELISA test. Less than 1% of the total amount of injected HPL* molecules was found to have adsorbed to the oil-water interface, and no significant effects of colipase on HPL* binding were observed. No significant changes in the hydrolysis rates or the binding of HPL* were detected in the presence of bile salts at concentrations ranging from below their critical micellar concentration (CMC) up to 100 microM. At the oil-water interface, in the absence or presence of bile salts below their CMC, it can be concluded that the colipase is a true lipase cofactor, i.e, it increases the enzyme turnover (approximately 10-15-fold) and does not affect the interfacial lipase adsorption.
The surface behaviour of two bile salts, sodium deoxycholate (NaDC) and sodium taurodeoxycholate ... more The surface behaviour of two bile salts, sodium deoxycholate (NaDC) and sodium taurodeoxycholate (NaTDC), as well as that of tetrahydrolipstatin (THL), a potent gastrointestinal lipase inhibitor, was studied at air/water and oil/water interfaces, using interfacial tensiometry methods. The surface behaviour of NaDC and NaTDC was comparable at both oil/water and air/water interfaces. A fairly compact interfacial monolayer of bile salts is formed well below the critical micellar concentration (CMC) and can help to explain the well-known effects of bile salts on the kinetic behaviour of pancreatic lipases. Using the Wilhelmy plate technique, the surface pressure-molecular area curves recorded with THL at the air/water interface showed a collapse point at a surface pressure of 24.5 mN.m(-1), corresponding to a molecular area of 70 A(2). Surprisingly, using the oil drop method, a limiting molecular area of 160 A(2) was found to exist at the oil/water interface. On the basis of the above data, space-filling models were proposed for bile salts and THL at air/water and oil/water interfaces.
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Papers by Alain Cagna