Iodination of monoclonal IgG antibodies at a sub-stoichiometric level: immunoreactivity changes related to the site of iodine incorporation

Int J Rad Appl Instrum B. 1987;14(5):451-7. doi: 10.1016/0883-2897(87)90109-7.


Thirteen monoclonal antibodies (MAbs) were labeled with 125I to a different degree such as to cover the range from 0.5-20 microCi/micrograms. By SDS polyacrylamide gel electrophoresis, the amount of iodine incorporated into heavy (h) and light (l) chains was determined. Comparing different MAbs, h:1 ratios varied from 0.6-34.6, but virtually no variation was observed with individual MAbs labeled at different levels. Immunoreactivity of labeled MAbs was analyzed with antigen-positive tumor cells according to the Lineweaver Burk method. Immunoreactive fractions were found to decrease with increasing iodine incorporation in 9/12 MAbs, while binding affinities decreased in 5/12 MAbs; only 1 MAb was stable in both respects. Immunoreactivity changes were not linked to preferential h or 1 chain labeling, nor to the isotype. This result indicated incorporation of the first iodine atom to take place at individually distinct residues, with a minimum estimate of two or four sites, depending on whether preferential chain labeling or random incorporation took place. In cases where increasing labeling led to a gradual decrease of binding affinity, a shift in the spectrum of acceptor residues has to be assumed.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibodies, Monoclonal* / isolation & purification
  • Humans
  • Immunoglobulin G* / isolation & purification
  • Immunoglobulin Heavy Chains
  • Immunoglobulin Light Chains
  • Iodine Radioisotopes*
  • Kinetics
  • Melanoma / diagnostic imaging
  • Mice
  • Radioisotope Dilution Technique
  • Radionuclide Imaging
  • Rats


  • Antibodies, Monoclonal
  • Immunoglobulin G
  • Immunoglobulin Heavy Chains
  • Immunoglobulin Light Chains
  • Iodine Radioisotopes