Abstract
γG myeloma proteins are multichain molecules cross-linked by disulphide bridges. In γG1 and γG4 proteins four interchain bridges have been described: two joining the heavy chains and the other two the heavy and light chains. The interchain bridges in γG3 are remarkably different in their number and distribution. Seven of them appear to cross-link the molecule—two joining the heavy and light chains, and the other five binding the heavy chain. Only three of them are present in a heavy chain disease protein of the same type. The unique half cystines which bind the light chains to the γ1 and γ4 heavy chains are both found in similar sequences in the γ3 heavy chains under study. However in the γ3 heavy chains only the γ4-like sequence binds the light chains. Splitting between the two half cystine residues in the hinge peptide made it possible to show that one of them belonged to a parallel bridge, suggesting that the interheavy chain bridges in the other types of γG globulins also are parallel.
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