title: Radioactive probes for adrenocorticotropic hormone receptors.
abstract: Our attempts to develop adrenocorticotropic hormone (ACTH) analogues that can be employed for ACTH receptor identification and isolation began with the synthesis of ACTH fragments containing N epsilon-(dethiobiotinyl)lysine (dethiobiocytin) amide in position 25 to be used for affinity chromatographic purification of hormone-receptor complexes on Sepharose-immobilized avidin resins. Because labeling ACTH or ACTH fragments by conventional iodination techniques destroys biological activity due to oxidation of Met4 and incorporation of iodine into Tyr2, we have prepared [Phe2,Nle4]ACTH1-24, [Phe2,Nle4,biocytin25]ACTH1-25 amide, and [Phe2,Nle4,dethiobiocytin25]ACTH1-25 amide by conventional synthetic techniques. The HPLC profiles and amino acid analyses of the final products indicate that the materials are of a high degree of purity. The amount of tertiary butylation of the Trp residue in the peptides was assessed by NMR and was found to be less than 0.5%. All three peptides are equipotent with the standard ACTH1-24 as concerns their ability to stimulate steroidogenesis and cAMP formation in bovine adrenal cortical cells. Iodination of [Phe2,Nle4]ACTH1-24, with iodogen as the oxidizing agent, has been accomplished without any detectable loss of biological activity. The mono- and diiodo derivatives of [Phe2,Nle4]ACTH1-24 have been prepared, separated by HPLC, and assayed for biological activity. Both peptides have the full capacity to stimulate steroidogenesis and cAMP production in bovine adrenal cortical cells.
mesh_terms: D000324:Adrenocorticotropic Hormone / Q000031:analogs & derivatives* / Q000138:chemical synthesis* / Q000378:metabolism; D001710:Biotin; D002250:Carbon Radioisotopes; D055598:Chemical Phenomena; D002621:Chemistry; D002851:Chromatography, High Pressure Liquid; D007202:Indicators and Reagents; D007457:Iodine Radioisotopes; D009682:Magnetic Resonance Spectroscopy; D009904:Optical Rotation; D010446:Peptide Fragments / Q000138:chemical synthesis; D011865:Radioisotope Dilution Technique; D011956:Receptors, Cell Surface / Q000378:metabolism*; D018043:Receptors, Corticotropin
chemical_list: D002250:Carbon Radioisotopes; D007202:Indicators and Reagents; D007457:Iodine Radioisotopes; D010446:Peptide Fragments; D011956:Receptors, Cell Surface; D018043:Receptors, Corticotropin; D001710:Biotin; D000324:Adrenocorticotropic Hormone