A photoactivatable naltrexone derivative labels glycoproteins of different molecular weight corresponding to the mu- and kappa-opioid receptors.
The synthesis and characterization of a novel opioid receptor photoaffinity probe [3H]naltrexyl urea phenylazido derivative ([3H]NUPA) is described. In the absence of light, [3H]NUPA binds with high affinity in a reversible and saturable manner to rat brain and guinea pig cerebellum membranes. Dissociation constants and binding capacities (Scatchard plots) are 0.11 nM and 250 fmol/mg of protein for rat brain and 0.24 nM and 135 fmol/mg of protein for guinea pig cerebellum. Competition experiments indicate that this ligand interacts with high affinity at both mu- and kappa-opioid binding sites while exhibiting low affinity at delta sites (Ki = 21 nM). On irradiation, [3H]NUPA incorporates irreversibly into rat brain and guinea pig cerebellum membranes. SDS gel electrophoresis of rat brain membranes reveals specific photolabeling of a 67-kDa molecular mass band. Conversely, a major component of 58 kDa and a minor component of 36 kDa are obtained from [3H]NUPA-labeled guinea pig cerebellum membranes. Different photolabeling patterns are obtained in rat brain (mu/delta/kappa, 4/5/1) and guinea pig cerebellum (mu+delta/kappa, 1,5/8,5) membranes in the presence of selective opioid ligands indicating labeling of mu and kappa sites, respectively. Thus, [3H]NUPA behaves as an efficient photoaffinity probe of mu- and kappa-opioid receptors, which are probably represented by distinct glycoproteins of 67 and 58 kDa, respectively.
Mejean
A
A
Laboratoire de Chimie Bio-Organique associé au CNRS (U.R.A. 1386), Faculté de Pharmacie, Université Louis Pasteur, Strasbourg, Illkirch, France.
Hawkinson
J
J
Guthapfel
R
R
Goeldner
M
M
Hirth
C
C
D000345:Affinity Labels; D000818:Animals; D001667:Binding, Competitive; D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry; D002531:Cerebellum / Q000737:chemistry; D006023:Glycoproteins / Q000032:analysis*; D006168:Guinea Pigs; D008970:Molecular Weight; D009271:Naltrexone / Q000737:chemistry; D010777:Photochemistry; D051381:Rats; D017473:Receptors, Opioid, kappa / Q000032:analysis*; D017450:Receptors, Opioid, mu / Q000032:analysis*
D000345:Affinity Labels; D006023:Glycoproteins; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D009271:Naltrexone