Motions studies of the human alpha 1-acid glycoprotein (orosomucoid) followed by red-edge excitation spectra and polarization of 2-p-toluidinylnaphthalene-6-sulfonate (TNS) and of tryptophan residues.

Dynamics studies on tryptophan residues of human alpha 1-acid glycoprotein (orosomucoid) and of 2-p-toluidinylnaphthalene-6-sulfonate bound to the protein are performed. Excitation at the red edge of the absorption spectrum of the tryptophan does not lead to a shift of the fluorescence emission maximum of the fluorophore. This reveals that Trp residues present motions with respect to their microenvironment. This is confirmed by polarization studies as a function of temperature. Excitation at the red edge of the absorption spectrum of TNS leads to an important shift (15 nm) of the fluorescence emission maximum of the probe. This reveals that emission of TNS occurs before relaxation of the amino-acids dipole occurs. Emission from a non-relaxed state means that TNS molecules are bound tightly to the protein, a result confirmed by polarization studies.