/sup 3/H)-(H-D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2) ((/sup 3/H)CTOP), a potent and highly selective peptide for mu opioid receptors in rat brain
The cyclic, conformationally restricted octapeptide (3H)-(H-D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2) ((3H)CTOP) was synthesized and its binding to mu opioid receptors was characterized in rat brain membrane preparations. Association rates (k+1) of 1.25 x 10(8) M-1 min-1 and 2.49 x 10(8) M-1 min-1 at 25 and 37 degrees C, respectively, were obtained, whereas dissociation rates (k-1) at the same temperatures were 1.93 x 10(-2) min-1 and 1.03 x 10(-1) min-1 at 25 and 37 degrees C, respectively. Saturation isotherms of (3H)CTOP binding to rat brain membranes gave apparent Kd values of 0.16 and 0.41 nM at 25 and 37 degrees C, respectively. Maximal number of binding sites in rat brain membranes were found to be 94 and 81 fmol/mg of protein at 25 and 37 degrees C, respectively. (3H)CTOP binding over a concentration range of 0.1 to 10 nM was best fit by a one site model consistent with binding to a single site. The general effect of different metal ions and guanyl-5'-yl-imidodiphosphate on (3H)CTOP binding was to reduce its affinity. High concentrations (100 mM) of sodium also produced a reduction of the apparent mu receptor density. Utilizing the delta opioid receptor specific peptide (3H)-(D-Pen2,D-Pen5)enkephalin, CTOP appeared to be about 2000-fold more specific for mu vs. delta opioid receptor than naloxone. Specific (3H)CTOP binding was inhibited by a large number of opioid or opiate ligands.
- Research Organization:
- Univ. of Arizona Health Sciences Center, Tucson (USA)
- OSTI ID:
- 6470418
- Journal Information:
- J. Pharmacol. Exp. Ther.; (United States), Vol. 248:1
- Country of Publication:
- United States
- Language:
- English
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ENDORPHINS
RECEPTORS
PEPTIDES
BIOCHEMICAL REACTION KINETICS
BRAIN
CELL MEMBRANES
ENKEPHALINS
IN VITRO
RATS
SODIUM
SOMATOSTATIN
TRACER TECHNIQUES
TRITIUM COMPOUNDS
ALKALI METALS
ANIMALS
AUTONOMIC NERVOUS SYSTEM AGENTS
BODY
CELL CONSTITUENTS
CENTRAL NERVOUS SYSTEM
DRUGS
ELEMENTS
ISOTOPE APPLICATIONS
KINETICS
LABELLED COMPOUNDS
MAMMALS
MEMBRANE PROTEINS
MEMBRANES
METALS
NERVOUS SYSTEM
NEUROREGULATORS
ORGANIC COMPOUNDS
ORGANS
POLYPEPTIDES
PROTEINS
REACTION KINETICS
RODENTS
VERTEBRATES
550201* - Biochemistry- Tracer Techniques