Abstract
Antigenic structure of the browning product between β-lactoglobulin and lactose (Lacβ-Lg) was studied by chemical modification and fragmentation. On immunoelectrophoretic analysis, S-carboxymethylated β-lactoglobulin (SCM β-Lg) and S-carboxymethylated Lac-β-Lg (SCM Lac-β-Lg) formed a precipitate line with anti Lac-β-Lg serum, while the both proteins did not form any precipitate line with antiserum to native β-Lg. Both products of cyanogen bromide cleavages of SCMβ-Lg and SCM Lac-β-Lg were divided into four fractions by gel filtration on Sephadex G-100. Antigenic activity, assayed by a passive cutaneous anaphylaxis inhibition test using antiserum to Lacβ-Lg, was retained in both fragments obtained by cyanogen bromide cleavages of SCM β-Lg and SCM Lac-β-Lg, and one of the common antigenic fragments was identified in the primary structure of β-Lg to be peptide 25-107. Contrary, none of these fragments inhibited on passive cutaneous anaphy1axis test using β-Lg and antiserum to nativeβ-Lg. These results indicate that Lac-β-Lg has antigenic determinants which are not affected by the conformational changes caused by S-carboxymethylation and cyanogen bromide cleavages, and also suggest that some of the antigenic determinants in Lac-β-Lg are probably formed as a result of irreversible alterations in the shape of β-Lg molecule by the heat treatment used for the preparation of Lac-β-Lg.
