The structural diversity (heterogeneity) problem of antibodies has become a big subject along with the development of antibody drugs and catalytic antibodies. The detailed studies on the subject have not been conducted because many difficult and complex problems are existed in the phenomena. The heterogeneity problem is observed in a whole antibody as well as a catalytic antibody. The difficulty and complexity of the heterogeneity are in the generation of many isoforms caused by different charges, different molecular sizes, and/or modifications of amino acid residues. We found that the constant region domain of the antibody light chain also plays an important role in the heterogeneity. It is desirable that the antibody and/or the subunits must have a defined structure for practical use. We found interesting phenomena that copper ion can convert the multi-molecular forms of antibodies to mono-molecular forms. The ion contributed greatly to the enrichment of the dimer-form and the homogenation of the differently charged full-length and constant region domain of the light chain. The role of copper ion must be significant for preparing a single, defined, not multiple, isoform structure. Note that the big problem could be solved by using copper ion during the purification process.
Part of the book: Antibody Engineering