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 gamma1 and gamma2 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.