Radiolabelling by tritium and [125I]iodine of an angiotensin II related peptide

We describe the 3H- and 125I- labelling of Glu-Gly-Val-Tyr-Val-His-Pro-Val, (hIIA), an octapeptide encoded by an RNA strand complementary to the human angiotensin II (AII) mRNA. The labelling of this peptide with 125I was performed in two ways: 1:, mono-iodination of the Tyr residue, using Na125I in the presence of Chloramine T; 2: coupling of the [125I]Bolton-Hunter reagent to the terminal amine group of the octapeptide. The synthesis of the tritiated (3,5-3H2-Tyr4)octapeptide was achieved by a two step synthesis: di-iodination of the peptide followed by its catalytic dehalogenation in the presence of tritium gas. The compounds obtained inhibited the binding of AII to its receptors or antibodies but showed no direct binding to these proteins, suggesting no competition between AII and hIIA for these protein binding sites. (author)