Tyrosylation and purification of peptides for radioiodination

A simple method for tyrosylation, purification and subsequent radioiodination of peptides which lack suitable acceptor groups for iodine substitution is presented. The reagent, tert.-butyloxycarbonyl-L-tyrosine N-hydroxysuccinimide ester, was used for conjugation to the amino groups of peptides. The derivatization was performed with relatively large amounts of reagents to ensure quantitative reactions. The derivatized peptides were purified by reversed-phase high-performance liquid chromatography or by gel filtration. Subsequent radioiodination was performed with sodium [125I]iodide and the sparingly soluble tetrachlorodiphenylglycouril as the oxidative agent to minimize possible oxidative damage to the peptides. The radiolabelled peptides were subsequently purified by isocratic high-performance liquid chromatography.