Fluorospectrometric analysis of heparin interaction with fibroblast growth factors

The fluorescence emission of a single tryptophan residue present in both FGF-1 and FGF-2 was used as a structural probe to directly assess the interaction of the growth factors with heparin or beta-cyclodextran tetradecasulfate. About 20-25% of the fluorescence of either FGF-1 or FGF-2 is quenchable, and is dependent on sulfation of the ligands. The quenchable fluorescence is associated with about 20% of total FGF, suggesting the presence of two fluorospectrometric forms of the protein. The equilibrium dissociation constants, determined by this method, for heparin or beta-cyclodextrin tetradecasulfate binding to FGF-1 are about 1 nM, whereas the values for FGF-2 are 1 and 23 nM, respectively. The method provides a direct tool to evaluate FGF-ligand interaction and assess the structural integrity of the proteins.