Immunoglobulin G Antibodies from an Individual Rabbit in Which Several Heavy Chain Variants Are Paired with One Light Chain Sequence

CNBr cleavage of rabbit heavy chain leads to the formation of a fragment, C1, which consists of the NH2-terminal half of the heavy chain. Fragment C1 is cleaved at methionyl residues but held together by intrachain S—S bonds to that total reduction and alkylation liberates new fragments. In the case of the C1 fragment from an anti-p-azobenzoate antibody of restricted heterogeneity, total reduction, and alkylation liberated six fragments which were isolated in good yield. Small amounts of other fragments were apparent. The six fragments were identified on the basis of molecular weights, amino acid compositions, and NH2-terminal sequences and represent residues 1 to 253, 1 to 34, 1 to 55, 56 to 140, 141 to 253, and 85 to 253. There was no evidence of acid splits, incomplete CNBr cleavage, or incomplete reduction. From the known positions of half-cystine residues and the fact that some of these fragments represent overlapping regions, it appears that heavy chains having different distributions of methionine are present. Therefore this heavy chain is not homogeneous. In contrast, the light chain from this antibody preparation appears to be homogeneous. This indicates that a limited set of different heavy chains may be paired with a single light chain to generate related antibody molecules.