| Abstract: | Guinea pigs were injected with 35S-amino acids and their sera were subsequently used as a source of labelled complement. The adsorption of radioactivity from such sera by specific immune precipitates and by insoluble, suspended, denatured proteins was studied under various experimental conditions. It was found that heat-inactivation of the serum sharply reduced the radioactivity carried down as did the addition of ethylene diamine tetraacetic acid to fresh serum. The latter effect could be overcome by the addition of calcium and magnesium ions. The addition of fresh unlabelled guinea-pig serum to heat-inactivated labelled guinea-pig serum increased the radioactivity adsorbed by the immune precipitates. This indicated that, when the heat-labile components of complement are thus supplied, the labelled heat-stable components can again be adsorbed. This effect of unlabelled complement could not be obtained with labelled serum that had been treated with hydrazine. It was also shown that the heat-stable, hydrazine-sensitive component was present in midpiece and absent from endpiece, indicating that it was not C′4, but probably a component of C′3. The adsorption of active C′1 by some heat-denatured suspended serum protein preparations was demonstrated. |
