Peptide analyses have been carried out for chymotryptic digests of transferrin C and transferrin D(1). There is a difference in one peptide, and amino acid analyses indicate that an aspartic acid residue in transferrin C is replaced probably by a glycine residue in transferrin D(1).
The existence of disulfide-bonded immunoglobulin (Ig) complexes of IgM-IgA, IgM-IgG, and IgM-IgG, in addition to a monoclonal IgM (kappa) paraprotein, free kappa chains and fragments of IgG (FIgG), were found in the plasma of a multiple gammopathy patient. This is the first report on the interclass disulfide-bonded Ig complexes. Upon exposure to a dissociating buffer containing 6 M urea, 0.1 M Tris-HCl, pH 8.0, a small portion of the IgM-IgA complexes and most of the IgM-IgG as well as the IgM-FIgG complexes dissociated, but the majority of the IgM-IgA and small amounts of other complexes remained intact. These intact complexes were not the result of antigen-antibody reactions and were apparently held together by disulfide bonds which could be broken into monomeric Ig basic units (H-L)2 and smaller components by mild reduction and alkylation.
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