Surface behaviour of bile salts and tetrahydrolipstatin at air/water and oil/water interfaces

The surface behaviour of two bile salts, sodium deoxycholate (NaDC) and sod ium 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 be haviour of NaDC and NaTDC was comparable at both oil/water and air-water in terfaces. A fairly compact interfacial monolayer of bile salts is formed we ll 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-molecula r area curves recorded with THL at the air/water interface showed a collaps e point at a surface pressure of 24.5 mN.m(-1). corresponding to a molecula r area of 70 Angstrom (2). Surprisingly, using the oil drop method. a limit ing molecular area of 160 Angstrom (2) was found to exist at the oil/water interface. On the basis of the above data, space-filling models were propos ed for bile salts and THL at air/water and oil/water interfaces. (C) 2001 E lsevier Science Ireland Ltd. All rights reserved.