Colicine K. III. The immunological properties of a substance having colicine K activity.

By immunological means it has been shown that colicine K is associated with the O antigen of the colicinogenic bacillus E. coli K(235) L(+)OC(+). The colicine K-O antigen complex elicits the formation of at least two types of antibodies, one a precipitin, the other a colicine-neutralizing antibody. The first precipitates colicine K without neutralizing it, the second neutralizes the colicine without precipitating it. Unlike the purified colicine K complex, the colicine protein component of the O antigen is precipitable by the neutralizing antibody. There is no demonstrable serological relationship between colicine K and phage T(6). These two agents must be considered to be separate and distinct entities.