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  • Title: Photoaffinity labeling of the beta-adrenergic receptor with azide derivatives of iodoccyanopindolol.
    Author: Burgermeister W, Hekman M, Helmreich EJ.
    Journal: J Biol Chem; 1982 May 10; 257(9):5306-11. PubMed ID: 6279665.
    Abstract:
    Two photosensitive iodocyanopindolol derivatives, 1-(4-azidobenzimidyl)-3,3-dimethyl-6-hydroxy-7-(2-cyano-3-iodoindol-4-yloxy)-1,4-diazaheptane (ICYP-azide-1) and 1-(4-azidobenzoyl)-3,3-dimethyl-6-hydroxy-7-(2-cyano-3-iodoindol-4-yloxy)-1,4-diazaheptane (ICYP-azide-2) have been prepared. [125I]ICYP-azide-1 and -2 (specific radioactivity up to 2.2 Ci/mumol) bind specifically and with very high affinity (KD = 40-45 pM) to beta-adrenergic receptors of turkey erythrocyte membranes. When [125I]ICYP-azide-1 or -2 were incubated with membranes and UV-irradiated, two polypeptides (Mr = 40,000 and 50,000) were specifically photolabeled as shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These polypeptides may represent subunits of the beta-adrenergic receptor. The yield of specific covalent label incorporation into both polypeptides was up to 17.2% with [125I]ICYP-azide-2 when expressed as fraction of total beta-receptor binding sites. Since the Mr = 40,000 polypeptide was labeled predominantly and since covalent incorporation had the same concentration dependence as reversible specific binding, this polypeptide could contain a beta-adrenergic ligand binding site. Due to the low working concentration (10-100 pM) of [125I]ICYP-azide-1 and -2, nonspecific labeling of membrane proteins was extremely low. The new photoaffinity labels should therefore become valuable tools for probing beta-receptor structure.
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