Abstract
Methods for the extraction and purification of the immobilization antigens of Paramecium aurelia have been developed. The immobilization antigen was shown to be a protein of molecular weight 250,000. The amino acid content of 2 allelic antigens and 1 controlled by a separate genetic locus was determined and many differences were observed. The properties of antigen denatured by reduction and alkylation were examined. The molecular weight fell to 80,000 or perhaps less. Peptide maps of allelic types were more similar than those of types controled by different genetic loci. It is suggested that the antigen consists of 2 identical half-molecules held together by disulphide bonds. These half-molecules may contain further sub-units.