The 28k and 70k dalton polypeptide components of mouse Ra-reactive factor are responsible for bactericidal activity.

Ra-reactive factor is a complement-dependent bactericidal factor that reacts specifically with Ra chemotype strains of Salmonella, and is ubiquitous in sera of a wide variety of vertebrates. Here we prepared an antiserum by immunizing rabbit with mouse Ra-reactive factor. This serum neutralized markedly the bactericidal activity of the factor. This action of the antiserum was inhibited by the factor whose bactericidal activity has been inactivated by heating for 30 min at 55 degrees C. Component polypeptides with apparent molecular weights of 28k and 70k in the factor were separated by SDS-polyacrylamide gel electrophoresis. They were also found to inhibit the antiserum activity. This indicates that these polypeptides carry the active site of the factor.