CONFORMATIONAL-CHANGES OF BOVINE SERUM-ALBUMIN UPON ITS ADSORPTION IN DODECANE-IN-WATER EMULSIONS AS REVEALED BY FRONT-FACE STEADY-STATE FLUORESCENCE

Front-face fluorescence spectroscopy was used to characterise dodecane-in-buffer (0.1 M phosphate buffer, pH = 7.6) emulsions stabilised by bovine serum albumin (BSA). A 15-nm blue-shift of the emission maximum of the adsorbed protein and a significant increase of its fluorescence quantum yield were observed. The contribution of tyrosyl residues to total fluorescence was tentatilely evaluated from difference spectra and an R ratio taking into account the stray-light interference; R increased upon BSA adsorption but the Tyrosine contribution remained weak in all cases. Thus, conformational changes of the protein take place upon BSA adsorption onto the dodecane-water interface. They involve modifications in the environment of the protein aromatic amino acids especially of the tryptophanyl residues which are displaced to a more hydrophobic location. Moreover, the proportions of adsorbed and non-adsorbed BSA in emulsions can be estimated from the position of the emission maximum.