Covalent linkage of ruthenium polypyridyl compounds to poly(L-lysine), albumins, and immunoglobulin G

Usually, labeling of proteins involves the modification of amino acid side chains. These include tyrosines, the e-amino groups of lysines, carboxyl groups of glutamic and aspartic acids, and sulfhydryl groups generated by mild reduction of cysteines (14). The site at which modification takes place has special significance when labeling of immunoglobulins is involved. The polypeptide moieties of immunoglobulins impart their specific antigen binding ability, and modification of the amino acid side chains may result in partial or complete loss of immunological activity. In contrast, the carbohydrate moieties of immunoglobulins are not involved in the antigen binding properties of these molecules, and modification should not directly affect antigen binding (15). The albumins and IgG have therefore been conjugated to the reporter molecule through both the e-amino group of the lysine residues and also through modification of the carbohydrate moieties on these proteins.