Isolation and Characterization of the Cyanogen Bromide Fragments of a Mouse γG Immunoglobulin

In order to isolate fragments suitable for amino acid sequence analysis, MOPC 173, a murine γG2a clonal immunoglobulin was cleaved with cyanogen bromide. On the basis of the methionine content of the molecule (2 residues for the light chains and 9 for the heavy chains), 13 fragments were expected to be released upon CNBr action. All 13 predicted fragments were isolated, either from the whole molecule or from its polypeptide chains and papain split Fab and Fc fragments. They were characterized by means of amino acid analysis, molecular weights as determined from gel filtration on Sephadex, NH 2 ‐terminal analysis and COOH‐terminal determination. They accounted for the whole molecule. Chemical evidence allowed ordering of the light chain derived fragments. The heavy chain derived fragments were unequivocally assigned to the Fd or to the Fc portion of the chain. Three of them were positioned on the grounds of chemical evidence, the remainder beeing ordered by assuming homology with a human γG immunoglobulin of known sequence.