Mu heavy-chain disease--a defect in immunoglobulin assembly. Structural studies of the kappa chain.

Mu-chain protein GLI is a pentameric molecule with an amino-terminal deletion comprising 130 residues. The half-cysteine residue (position 140) which forms the H-L disulfide bridge in normal IgM is present. Instead of being joined to the L chain, it presumably exists as an additional inter-H-H disulfide bridge. The kappa Bence Jones protein is of normal size and present in two forms: as monomers and dimers. The carboxy-terminal half-cysteine of the monomer is bound to cysteine. Possible reasons for failure of assembly between mu and L chains are briefly discussed.