Antigenic Reactivities of Fragments Obtained by Cyanogen Bromide Cleavage of Bovine α_s1-Casein toward Antiserum to Intact α_s1-Casein

Abstract

To study the preliminary localization of the antigenic sites of bovine α_s1-casein, we separated fragments 1-54, 55-60, 61-123, 124-135, 136-196 and 197-199 from α_s1-casein cleaved with cyanogen bromide, and examined the antigenic reactivities of the fragments with antiserum to intact α_s1-casein.
On quantitative precipitation between a_sl-casein and its antiserum, a mixture of fragments 1-54, 55-60, 61-123, 124-135, 136-196 and 197-199 inhibited the formation of immune precipitates by 84.2%. Four of these six fragments, i.e. fragments 1-54, 61-123, 124-135 and 136-196, still showed high antibody-binding activities in the quantitative immunoprecipitin inhibition test and an enzyme-linked immunosorbent assay. Furthermore, on immunodiffusion analysis, only fragment 61-123 formed a single and sharp precipitin arc.
These results indicate that at least one antigenic site of α_s1-casein is associated with each of regions 1-54, 124-135 and 136-196, and more than two with region 61-123.