SECONDARY STRUCTURE CHANGES AND PEPTIC HYDROLYSIS OF BETA-LACTOGLOBULIN INDUCED BY DIOLS

The addition of ethylene glycol, and 1,2- and 1,3-propanediol, decreas es the bulk dielectric constant of the medium, and according to CD mea surements, increases significantly the proportion of helical structure in beta-lactoglobulin. The medium-induced folding changes followed by limited peptic hydrolysis show that the cleavage of beta-lactoglobuli n by pepsin is triggered by structural transformations induced by ethy lene glycol only and not by 1,2- and 1,3-propanediol. Density measurem ents, al constant chemical potential and constant molality, demonstrat e that all diols are present in the immediate domain of the protein. T hey are engaged in hydrophobic interactions with the amino acids of be ta-lactoglobulin core inducing the formation of additional alpha-helic es. (C) 1996 John Wiley & Sons, Inc.