Photoaffinity labeling of the. cap alpha. /sub 1/-adrenergic receptor using an /sup 125/I-labeled aryl azide analogue of prazosin. [Rats]

Journal Article · Tue Jul 31 04:00:00 EDT 1984 · Biochemistry; (United States)

OSTI ID:6355383

Seidman, C E; Hess, H J; Homcy, C J; Graham, R M

..cap alpha../sub 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-dimethoxyquinazoline (CP63,155), an arylamine analogue of the selective ..cap alpha../sub 1/-adrenergic antagonist prazosin, and its iodinated derivative, 2-(4-(4-amino-3-(/sup 125/I)iodobenzoyl)piperazin-1-yl)-4-amino-6,7-dimethoxyquinazoline ((/sup 125/I)CP63,789), bind reversibly and with high affinity (K/sub D/ = 1 nM and 0.6 nM, respectively) to rat hepatic membrane ..cap alpha../sub 1/-adrenergic receptors. Conversion of (/sup 125/I)CP63,789 to the aryl azide yields a photolabile derivative, 2-(4-(4-azido-3-(/sup 125/I)iodobenzoyl)piperazin-1-yl)-4-amino-6,7-dimethoxyquinazoline ((/sup 125/I)CP65,526), which prior to photolysis binds competitively and with high affinity (K/sub D/ = 0.3 nM). Binding of (/sup 125/I)CP63,789 and (/sup 125/I)CP65,526 (prior to photolysis) is rapid and saturable. Both ligands identify similar ..cap alpha../sub 1/-adrenergic receptor binding site concentrations as the parent probe, (/sup 3/H)prazosin. Specific binding by these iodinated ligands is stereoselective and inhibited by a variety of adrenergic agents with a specificity typical of the ..cap alpha../sub 1/-adrenergic receptor. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and autoradiography of (/sup 125/I)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 ..cap alpha../sub 1/-adrenergic receptor. Smaller peptides with molecular weights of 42K and 31K display prazosin-inhibitable (/sup 125/I)CP65,526 binding. Labeling of these protein species with (/sup 125/I)CP65,526 is not inhibitable by other adrenergic agonists or antagonists. They are thus unlikely to represent subunits of the receptor.

• Research Organization: Massachusetts General Hospital, Boston
• OSTI ID: 6355383
• Journal Information: Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 23:16; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ANIMAL CELLS
ANIMALS
AUTONOMIC NERVOUS SYSTEM AGENTS
AUTORADIOGRAPHY
AZIDES
BETA DECAY RADIOISOTOPES
BIOCHEMICAL REACTION KINETICS
CELL CONSTITUENTS
CELL MEMBRANES
DAYS LIVING RADIOISOTOPES
DRUGS
ELECTRON CAPTURE RADIOISOTOPES
HALOGEN COMPOUNDS
INTERMEDIATE MASS NUCLEI
IODINE 125
IODINE COMPOUNDS
IODINE ISOTOPES
ISOTOPES
KINETICS
LABELLED COMPOUNDS
LABELLING
MAMMALS
MEMBRANES
MOLECULAR BIOLOGY
NITROGEN COMPOUNDS
NUCLEI
ODD-EVEN NUCLEI
RADIOISOTOPES
RATS
REACTION KINETICS
RECEPTORS
RODENTS
SYMPATHOLYTICS
SYMPATHOMIMETICS
TRITIUM COMPOUNDS
VERTEBRATES