Photoaffinity labeling of opiate receptors using intrinsically photoactive /sup 3/H-opiates
Opiate receptors in rat and cow brain membranes have been labeled irreversibly using the intrinsic photolability of 3H-opiates. Membranes were incubated with 3H-ligand and then irradiated with UV light of 254 nm. Nonspecific binding was determined in the presence of 10 microM unlabeled levallorphan. Irreversible binding was defined as binding which survived heat or acid denaturation of membranes. Specific incorporation of label into denatured samples was observed only when unbound or loosely bound 3H-ligand was washed free from the membranes prior to irradiation. There was a general correlation between photosensitivity of the 3H-ligand and its ability to photolabel receptors. Hence, photolabeling presumably results by covalent attachment of highly reactive species generated during photochemical decomposition of ligand. With 3H-etorphine, optimal irradiation time was 5 min. In addition to 3H-etorphine, receptors could be labeled irreversibly with 3H-oxymorphone, 3H-dihydromorphine, and 3H-ethylketocyclazocine. Of the specific binding present in irradiated, nondenatured samples, 45-60% remained attached to receptors upon denaturation. 3H-Ethylketocyclazocine exhibited an 86% yield of incorporation. Signal-to-noise levels of 50-80% could be achieved in denatured samples. Therefore, this method provides a means of covalently labeling opiate receptors in high yield and with high signal-to-noise ratios. The opioid peptides, 3H-D-Ala2,D-Leu5-enkephalin, 3H-D-Ser2,Leu5,Thr6-enkephalin, 3H-D-Ala2,Met5-enkephalin amide, and 3H-D-Ala2,N-MePhe4,Gly-ol5-enkephalin, as well as the benzomorphan, 3H-bremazocine, apparently lack the structural characteristics which allow photolabeling.
- Research Organization:
- Brown Univ., Providence, RI (USA)
- OSTI ID:
- 7154804
- Journal Information:
- Mol. Pharmacol.; (United States), Journal Name: Mol. Pharmacol.; (United States) Vol. 33:3; ISSN MOPMA
- Country of Publication:
- United States
- Language:
- English
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59 BASIC BIOLOGICAL SCIENCES
ANIMALS
AUTONOMIC NERVOUS SYSTEM AGENTS
BIOCHEMICAL REACTION KINETICS
BODY
BRAIN
CATTLE
CELL CONSTITUENTS
CELL MEMBRANES
CENTRAL NERVOUS SYSTEM
CENTRAL NERVOUS SYSTEM DEPRESSANTS
DOMESTIC ANIMALS
DRUGS
ELECTROMAGNETIC RADIATION
ENDORPHINS
IN VITRO
IRRADIATION
ISOTOPE APPLICATIONS
KINETICS
LABELLED COMPOUNDS
LABELLING
LIGANDS
MAMMALS
MEMBRANE PROTEINS
MEMBRANES
NARCOTICS
NERVOUS SYSTEM
NEUROREGULATORS
ORGANIC COMPOUNDS
ORGANS
PROTEINS
RADIATIONS
RATS
REACTION KINETICS
RECEPTORS
RODENTS
RUMINANTS
SIGNAL-TO-NOISE RATIO
TRACER TECHNIQUES
TRITIUM COMPOUNDS
ULTRAVIOLET RADIATION
VERTEBRATES