Isolation and Characterization of Active Fragments Obtained by Cleavage of Immunoglobulin G with Cyanogen Bromide

From the ¹ From the Section of Chemical Immunology, The Weizmann Institute of Science, Rehovoth, Israel

Treatment of rabbit immunoglobulin G with cyanogen bromide in 0.3 M HCl under specified conditions resulted in the cleavage of about half of its methionyl peptide bonds. A 5 S fragment was isolated from the reaction mixture by gel filtration in a quantitative yield. A comparison of the molecular weight and the amino acid composition of this fragment with the pepsin-produced 5 S fragment indicates that the latter is somewhat bigger than the CNBr 5 S fragment.

The CNBr 5 S fragment reacted fully with goat antiserum against papain digest Fragment I of rabbit immunoglobulin G, but, in contrast to native immunoglobulin G, did not react with goat antiserum against papain digest Fragment III. The CNBr 5 S fragment of rabbit antibody to bovine serum albumin retained the full capacity to precipitate the antigen, but did not respond in the passive cutaneous anaphylaxis test; the ability to fix complement was very markedly reduced.

Reduction of the CNBr 5 S fragment of the antibody with cysteine or 2-mercaptoethylamine led to the formation of a 3.3 S fragment, capable of reacting with bovine serum albumin but not of precipitating it. Reoxidation of the CNBr 3.3 S fragment resulted in a partial reformation of the 5 S fragment.

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