Forster energy-transfer studies between Trp residues of α1-acid glycoprotein (orosomucoid) and the glycosylation site of the protein

Energy-transfer studies between Trp residues of alpha(1)-acid glycoprotein and the fluorescent probe Calcofluor White were performed. Calcofluor White interacts with carbohydrate residues of the protein, while the three Trp residues are located at the surface (Trp-160) and in hydrophobic domains of the protein (Trp-25 and Trp-122). Binding of Calcofluor to the protein induces a decrease in the fluorescence intensity of the Trp residues accompanied by an increase of that of Calcofluor White. Efficiency (E) of Trp fluorescence quenching was determined to be equal to 45%, and the Forster distance R-o, at which the efficiency of energy transfer is 50%, was calculated to be 18.13 Angstrom. This low distance and the value of the efficiency clearly indicate that energy transfer between Trp residues and Calcofluor White is weak. (C) 2003 Elsevier Ltd. All rights reserved.