Interactions between bovine serum albumin and sodium taurodeoxycholate: thermodynamic properties

The solution properties of a commercial saponin obtained from Quillaja Bark (QBS), have been investigated in a wide range of experimental conditions in water and in the presence of moderate amounts of porcine skin gelatine, GEL. Saponins are surface active and form micelles at very low concentration. Significant changes in the solution dielectric properties are concomitant to micelle formation. The combination of thermodynamic, spectroscopic, transport and dielectric methods characterises the micelle formation, giving information on interactions between the components. NMR relaxation times, NMR self-diffusion and dielectric measurements were used. Micelle aggregation numbers, inferred from light scattering, indicate the formation of relatively large aggregates. No evidence for interactions between protein and surfactant was obtained. This is presumably due to the limited ionisation of acidic groups on the surfactant, which does not allow significant electrostatic binding with the protein.