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Peptide Radioiodination
Service Center
The rationale for this Service center is to make large quantities of 125I-labeled radioligands available to academic researchers for studies in which large amounts of radioligand are needed.
One such situation is saturation isotherm analyses of receptor binding. Ideally, one should use a full range of the radioligand, from very low subsaturating concentrations to near saturating concentrations of radioligand. Frequently, because of the high cost of radioiodinated ligands, investigators must use low, subsaturating concentrations of radioligand for receptor binding assays. As a result, only small proportions of the receptors are occupied with radioligand. Under such conditions it is difficult to determine the binding affinity (dissociation constant, Kd) of the radioligand and the amount of receptor (maximal binding capacity, Bmax) in the tissue preparation.
Another situation is in vitro receptor autoradiography in which a large number of tissue sections must be incubated with radioligand. Such incubations are best done in Coplin jars in which the slides containing the tissue sections can be completely and consistently bathed in the radioligand containing incubation solution. If large numbers of slides must be incubated, or if the investigator wishes to use a concentration of radioligand exceeding the Kd concentration to ensure good receptor occupancy, this requires large amounts of radioligand.
Since commercial vendors do not market millicurie quantities of 125I-labeled peptides, it would be cost prohibitive to attempt to purchase multiple microcurie-sized lots of 125I-labeled peptides from a commercial supplier to carry out the above noted types of experiments. Thus, this Service Center provides 125I-labeled peptides at amounts not generally available to researchers.
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