The Importance of Defined Tracers in RIA

Abstract

The radio-iodination of a peptide often leads to the production of heterogeneous mixtures due to monoiodination at different residues, iodination at more than one residue, diiodination at single residues, peptide damage (e.g. methionine oxidation), and the presence of underivatized peptide. Such mixtures often show chemical and radiochemical variations between preparations, and sub-optimal sensitivity in RIA. Regulatory peptides are often present in body tissues and fluids at very low concentrations and in different forms, such that very sensitive and specific assays are needed. These assays can be improved by the use of defined tracers, the use of which is now described for a range of iodinated peptides purified by RP-HPLC. These include human α-ANP®, insulin, VIP, glucagon, ß-endorphin, neurotensin, GRF, ACTE and IGF-1. RP-HPLC can produce carrier-free labelled peptides which are mono-iodinated at specific residues, leading to improved and consistent performance in RIA’s and RRA’s.