3H-Leu5-enkephalin specific binding to synaptic membrane-comparison with 3H-dihydromorphine and 3H-naloxone
Law, P.Y.; Loh, H.H.
Research Communications in Chemical Pathology and Pharmacology 21(3): 409-434
1978
ISSN/ISBN: 0034-5164 PMID: 705021 Document Number: 138106
Specific binding of 3H-Leu5. The association and disassociation rates and the dissociation constants of the enkephalin were affected to a larger degree than those of the opiates when the incubation temperature was altered from 0.degree.-37.degree. C. Although 100 mM Na+ inhibited 3H-Leu5-enkephalin binding, the magnitude of the Na+ inhibition was increased when the incubation temperature was raised from 25.degree.-37.degree. C. When the membrane was treated with N-ethylmaleimide or 3,5-diiodo-4-diazosulfanilic acid, selective inhibition of enkephalin, dihydromorphine and naloxone binding was observed. The affinities of various opioid peptides for 3H-Leu5-enkephalin were different than those for 3H-dihydromorphine. All alkaloids generally had a higher affinity for 3H-dihydromorphine binding sites than 3H-Leu5-enkephalin binding sites. The converse was the case with opioid peptides with the exception of .beta.-endorphin. 3H-Leu5-Enkephalin's interaction with the opiate receptor is distinctly different from those of the narcotic analgesics. This is an explanation for the low in vivo analgesic potency displayed by the enkephalins.