Binding of bromosulphthalein sodium by human serum albumin using a continuous diafiltration technique.

1. The recently introduced ultrafiltration-cum-dialysis technique termed continuous diafiltration has been used to obtain detailed binding isotherms of equilibrium solution concentration of bromosulphthalein (BSP) versus the number of molecules of BSP bound per molecule of human serum albumin for pure human serum albumin solutions (albumin concentrations: 1.59-3.39 g/100 ml) and for three dilutions of pooled human serum (albumin concentrations: 1.45-2.85 g/100 ml) in 310 ideal milliosmolar phosphate buffer at pH 7.4 and 22 degrees C.2. Qualitative analysis of the isotherms seems to indicate that there is a competition between the polymerization of the albumin to dimers and high oligomers and the binding of BSP by albumin.3. The binding capacity of pure human serum albumin at total BSP (bound and free) concentrations below 2.3 mM is greater than that of the pooled serum at an equivalent albumin concentration, possibly indicating the blockage of binding sites by more strongly binding ligands.4. The binding capacity of pure albumin at total BSP concentrations greater than 2.3 mM is less than that of pooled serum at an equivalent albumin concentration, suggesting the presence of other non-ultrafilterable materials in the serum capable of binding BSP.