Importance of Ribosome Purity in Ribosomal Serology

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Abstract
Antisera made from unwashed preparations of 50 S ribosomal subunits of Agrobacterium gave reproducible immuno-precipitation patterns when reacted with ammonium sulfate-washed ribosomes, but the patterns were not always reproducible when reacted with unwashed ribosomes. We suspected that this lack of reproducibility was due to a nonribosomal antigen associated with unwashed ribosomes. The association of this antigenic contaminant with the unwashed ribosomes was demonstrated when antiserum to heat-stable antigens of whole cells and antiserum to unwashed ribosomes reacted with both heat-stable antigens of whole cells and unwashed ribosomes to produce confluent precipitant bands. This contaminant was also associated with unwashed 50S subunits. The contaminant was removed by ammonium sulfate fractionation and the subsequent sedimentation of the ribosomes in the presence of 0.6 M ammonium sulfate. The contamination was not associated with other ammonium sulfate-washed ribosomes nor the proteins extracted from the highly purified 50 S subunits. Therefore, nonspecific binding of a somatic antigen to unwashed ribosomal particles appears to offer the most probable explanation for the additional antigenic response.