Thermodynamic properties of the bovine serum albumin-sodium taurodeoxycholate system

The interaction between bovine serum albumin, BSA, and sodium taurodeoxycholate, NaTDC, a component of the bile in mammals, has been investigated for several protein to surfactant ratios. The solution region was investigated by surface tension, sigma, freezing point depression, DeltaT, emf measurements, as well as by integral heat of dilution data, DeltaH(i,dil). The corresponding properties of NaTDC in aqueous solutions were investigated too. Surfactant binding onto the protein is controlled by a delicate balance of hydrophobic and electrostatic contributions, responsible for the adduct stability, but does not give rise to precipitation or coacervate formation, at least at pH around 6.0. The observed behaviour is in line with current knowledge on the solution behaviour of BSA-TDC complexes occurring in hepatic and gallbladder bile. (C) 2004 Elsevier B.V. All rights reserved.