Photoaffinity labeling of the alpha 1-adrenergic receptor using an 125I-labeled aryl azide analogue of prazosin

Biochemistry. 1984 Jul 31;23(16):3765-70. doi: 10.1021/bi00311a031.

Abstract

alpha 1-Adrenergic receptor probes, which can be radioiodinated to yield high specific activity radioligands, have been synthesized and characterized. 2-[4-(4-Amino-benzoyl)piperazin-1-yl]-4-amino-6,7-dimethoxyquin azoline (CP63,155), an arylamine analogue of the selective alpha 1-adrenergic antagonist prazosin, and its iodinated derivative, 2-[4-(4-amino-3-[125I]iodobenzoyl)piperazin-1-yl]-4-amino-6, 7-dimethoxyquinazoline [( 125I]CP63,789), bind reversibly and with high affinity (KD = 1 nM and 0.6 nM, respectively) to rat hepatic membrane alpha 1-adrenergic receptors. Conversion of [125I]CP63,789 to the aryl azide yields a photolabile derivative, 2-[4-(4-azido-3-[125I]iodobenzoyl)piperazin-1-yl]-4-amino-6, 7-dimethoxyquinazoline [( 125I]CP65,526), which prior to photolysis binds competitively and with high affinity (KD = 0.3 nM). Binding of [125I]CP63,789 and [125I]CP65,526 (prior to photolysis) is rapid and saturable. Both ligands identify similar alpha 1-adrenergic receptor binding site concentrations as the parent probe, [3H]prazosin. Specific binding by these iodinated ligands is stereoselective and inhibited by a variety of adrenergic agents with a specificity typical of the alpha 1-adrenergic receptor. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and autoradiography of [125I]CP65,526-labeled rat hepatic membranes reveal major protein species with molecular weights of 77K, 68K and 59K. Each protein binds adrenergic ligands with stereoselectivity and with a specificity typical of the alpha 1-adrenergic receptor. Inclusion of multiple protease inhibitors during membrane preparation prior to SDS-PAGE does not alter the labeling of these peptides.(ABSTRACT TRUNCATED AT 250 WORDS)

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Affinity Labels / chemical synthesis*
  • Animals
  • Azides / chemical synthesis*
  • Azides / metabolism
  • Binding, Competitive
  • Cell Membrane / metabolism
  • Female
  • Indicators and Reagents
  • Kinetics
  • Liver / metabolism
  • Molecular Weight
  • Prazosin / analogs & derivatives
  • Prazosin / metabolism
  • Quinazolines / chemical synthesis*
  • Quinazolines / metabolism
  • Rats
  • Rats, Inbred Strains
  • Receptors, Adrenergic, alpha / isolation & purification
  • Receptors, Adrenergic, alpha / metabolism*

Substances

  • Affinity Labels
  • Azides
  • Indicators and Reagents
  • Quinazolines
  • Receptors, Adrenergic, alpha
  • azidoprazosin
  • Prazosin