Some aspects of beta-lactoglobulin structural properties in solution studied by fluorescence quenching

The technique of protein fluorescence quenching by acrylamide and sodium nitrite (NO2-) was used to study some structural aspects of beta-lactoglobulin in solution. The degree of exposure and the micro-environments of the two tryptophanyl residues (Trp-19 and Trp-61) present in this ruminant milk protein were sensed, and the influence of the pH and the binding of palmitic acid in their accessibilities were analyzed. The results obtained showed that Trp-19 has an accessibility to the quenchers higher than could be supposed from its structural location. The binding of palmitic acid, on the other hand, increases the accessibility of both tryptophanyl residues, a fact that could be associated with a slight conformational change of the protein.