Use of retinoic acid as a fluorescent probe to study conformational change of the albumin molecule.

The binding of retinoic acid to serum albumin induces quenching of the protein fluorescence when it is excited at 280 nm, on the other hand the bound ligand acquires intrinsic fluorescence. Albumin has two kinds of binding sites for retinoic acid with an affinity constant of 10(5) M-1 and 10(4) M-1 respectively. The binding is entropically driven and produces a conformational change at the environment of the albumin tryptophan residues. This change was described by an equilibrium constant assuming two conformational states of the albumin tryptophan residues. Retinoic acid binds to the albumin fatty acid binding sites, producing a perturbation in the warfarin and benzodiazepine binding sites of this protein.