Physicochemical properties of maltosyl and glucosaminyl derivatives of beta-lactoglobulin.

Maltosyl and glucosaminyl derivatives of beta-lactoglobulin (b-LG) were analyzed for their physicochemical properties: reduced viscosity, ultraviolet difference spectra, intrinsic fluorescence, hydrophobicity and circular dichroism. The viscosity of these derivatives increased as the mass of the carbohydrates covalently linked to b-LG increased. The ultraviolet difference spectra and the intrinsic fluorescence of these proteins revealed that the microenvironments of aromatic amino acid residues of b-LG were increasingly exposed to the surface of the protein as the extent of modification increased; and the polarity of these residues also increased as modification increased. The hydrophobicities of M-b-LG derivatives decreased as the extent of modification increased while the hydrophobicities of G-b-LG derivatives were relatively unchanged. The circular dichroic analysis of these proteins indicated that the order secondary structures of the extensively modified derivatives of b-LG were partially unfolded. Thus, the carbohydrates covalently linked to b-LG altered many physiochemical properties. These physicochemical changes of b-LG apparently resulted from an alteration of forces stabilizing the structure of the protein.