Fluorescence spectroscopy evaluation of fibrinogen–β-estradiol binding

Fluorescence spectroscopy experiments were performed in order to study conformational changes induced by the binding of β-estradiol to fibrinogen at different ligand concentrations. The association constant (Ka) obtained for the fibrinogen–β-estradiol binding was 6.47 × 106 M−1, indicating a high affinity interaction. Fluorescence quenching experiments showed that approximately 30% of the tryptophan residues in the protein quaternary structure are accessible to ionic quenchers. The extent of quenching in the absence and presence of β-estradiol was maximum for cesium ions and minimum for iodide, suggesting the presence of negatively charged residues in the vicinity of the tryptophan residues. The quenching parameters obtained at different β-estradiol concentrations show alterations that confirm a conformational change, possibly due to a discrete reorganization of tryptophan residues during fibrinogen–β-estradiol binding. This binding may be responsible for the effects of β-estradiol on the decrease of erythrocyte aggregation and on cardiovascular risk reduction.