The position of various cleavages of rabbit immunoglobulin G.

The 5 S fragments of rabbit immunoglobulin G were prepared by digestion with pepsin or with CNBr. Cleavage of these fragments with trypsin led to the localization of the positions of these splits on the heavy chain. The COOHterminal residue released by carboxypeptidase A from the papsin-produced 5 S fragment was leucine. The pepsin-5 S fragment was reduced and aminoethylated to yield the 3.5 S fragment. Trypsin digestion of this fragment yielded two decapeptides which represent the COOH terminus of the heavy chain part of the 3.5 S fragment. The major one, obtained in 65 % yield, had the sequence