Thymopoietin32-36 (TPS) is a synthetic pentapeptide that has the biological activity of its parent molecule, the 49 amino acid thymic hormone thymopoietin.
Tritiated t h y m~p o i e t i n~~+~ (3 H-TP5) was prepared by reductive tritiation o f dibromotyrosyl-TPS. The stability o f 'H-TPS in human plasma was studied by analyzing samples by thin-layer chromatography at different time points and quantitating the radioactivity associated with TP5 (Arg-Lys-Asp-Val-Tyr) and its tyrosyl-con taining breakdown products (Lys-Asp-VaI-Tyr, Asp-Val-Tyr, Val-Tyr, Tyr). In plasma (but not in saline) the pentapeptide was rapidly degraded (apparent ttIz 30 seconds) with the corresponding appearance of radioactivityassociated with the other tyrosyl-containing reference compounds. These data imply that the pentapeptide, which is active in vivo, may rapidly trigger changes in responsive cells; sustained circulating levels may not be required for activity.
SUMMARYThymopentin (TP5, Arg-Lys-Asp-Val-Tyr), a synthetic pentapeptide corresponding to amino acids 32-36 of the thymic hormone thymopoietin, has the biological activity of the parent compound. The tyrosyl residue was iodinated using the chloramine-T method and the reaction mixture separated by HPLC into peaks corresponding to free TPS, mono-iodo TP5 and di-iodo TP5, identified by mass spectrometry. Biological activity was retained in the iodinated peptides but, surprisingly, free TP5 had lost biological activity during the separation process. The biologically active monoiodinated TP5 had a specific activity of 28 pCi/Pg and will be useful in studies of receptor binding.
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