Rapid and Efficient Radiolabeling of Short Peptides.

The use of peptides labeled with radioactive iodine isotopes enables rapid and highly sensitive assessment of their dynamic distribution in the body, as well as effective visualization and quantification of their metabolites in biological fluids and tissues down to femtomolar concentrations. In this work, we present the laboratory protocol for radioiodination of peptides containing oxidation-labile amino acids. Products of iodination of the histidine- and tyrosine-containing peptides were analyzed by NMR and high-performance liquid chromatography-high-resolution mass spectrometry (HPLC-HRMS) spectra. The proposed protocol describes a simple laboratory method for monitoring the extent of iodine isotope incorporation and a technique for isolating labeled peptides (3-10 amino acids) of high chemical and radiochemical purity without using HPLC. Using HPLC with fluorescence detection, we demonstrate the absence of significant oxidation of labile amino acids (Met, Trp, Tyr) during the radiolabeling process. The peptides labeled according to the protocol are obtained as lyophilizates with minimal inorganic salt content, allowing their direct use in cellular and animal model studies.