Comparative studies of sheep immunoglobulins IgG1 and IgG2: Amino acid sequence of carboxy‐terminal cyanogen bromide fragments from their heavy chains

Sheep immunoglobulin IgG1 and immunoglobulin IgG2 heavy chains were treated with cyanogen bromide. The fractions from the C‐terminal end of the heavy chains were isolated and purified, and the amino acid sequences of these fractions were determined. The C‐terminal octadecapeptides from γ1 and γ2 heavy chains had the identical sequence: Met‐His‐Glx‐Ala‐Leu‐His‐Asx‐His‐Tyr‐Thr‐Glx‐Lys‐Ser‐Ile‐Ser‐Lys‐Pro‐Pro‐Gly. Comparison with the C‐terminal peptides of other species, reported in the literature, suggests that the subclasses are the results of recent evolutionary processes. Residues at position 4 from the C‐terminus may be phylogenetically related.