Immunochemical studies on α-lactalbumin

Abstract

The antigenic structural features of α-lactalbumin have been investigated using a radioimmunoassay, peptide inhibition of the quantitative precipitin reaction, and by immunodiffusion analysis after chemical modification of the molecule. Antigenic activity (in rabbits) was localized to several peptic fragments and the single arginine residue of bovine α-lactalbumin. Antigenic activity was also found to be associated with the single methionine residue. A peptic fragment containing a disulfide loop was found to possess antigenic activity in both bovine and goat α-lactalbumin. Radioimmunoassay cross-reactivity between the α-lactalbumins is correlated with amino acid sequence similarities; bovine α-lactalbumin antiserum cross-reacts with goat α-lactalbumin more extensively than with human α-lactalbumin, while the more distantly homologous protein, chicken lysozyme, does not cross-react at all. Nevertheless our data indicate that the α-lactalbumins and lysozyme share a similar distribution of antigenic determinants on their surfaces.