Cleavage of bacterial flagellin with cyanogen bromide. Antigenic properties of the protein fragments.

1. Four polypeptide fragments, obtained by cyanogen bromide treatment of the protein flagellin from Salmonella adelaide, were tested for their antigenic activity by using them as inhibitors in three different assays: bacterial immobilization, haemagglutination of sensitized erythrocytes and quantitative micro precipitation. Immunodiffusion studies were also performed on the protein fragments. 2. Cleavage of the flagellin molecule in this way gave no detectable loss of antigenic determinants. Fragment A (mol.wt. 18000), the largest of the polypeptides, contained all the antigenic specificities present on flagellin that were recognized by the antisera used. In one test, fragment B (mol.wt. 12000) also contained antigenic activity to an extent not easily explainable by contamination with fragment A. Fragments C (mol.wt. 5500) and D (mol.wt. 4500) appeared to be antigenically inactive.