Dye covalently attached to lysine/cysteine side chain ... ?

Is the dye covalently attached to lysine or cysteine side chain in the antibody?
FAQ from Biotium
The dye is covalently attached to the side chains of amino acids located far away from the antigen-binding sites so that the affinity of the antibody is not affected. However, the exact attachment sites and the nature of chemical linkages are proprietary information.
FAQ from Biotium
The dye is covalently attached to the side chains of amino acids located far away from the antigen-binding sites so that the affinity of the antibody is not affected. However, the exact attachment sites and the nature of chemical linkages are proprietary information.