Förster energy-transfer studies between Trp residues of α 1-acid glycoprotein (orosomucoid) and the glycosylation site of the protein

Abstract

Energy-transfer studies between Trp residues of α 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 Förster distance R o, at which the efficiency of energy transfer is 50%, was calculated to be 18.13 Å. This low distance and the value of the efficiency clearly indicate that energy transfer between Trp residues and Calcofluor White is weak.