Irreversible labelling of the opioid receptors by a melphalan-substituted [Met5]enkephalin-Arg-Phe derivative.
[Met5]enkephalin-Arg-Phe (Tyr-Gly-Gly-Phe-Met-Arg-Phe) was modified with the methyl esther of melphalan (Mel; 4-bis(2-chloroethyl)amino-L-phenylalanine) and the resulting compounds were studied for their opioid binding properties in guinea pig and rat brain membranes. Three new peptides, with a substitution of a single amino acid, were synthesized (Mel-Gly-Gly-Phe-Met-Arg-Phe, Tyr-Gly-Gly-Mel-Met-Arg-Phe and Tyr-Gly-Gly-Phe-Met-Arg-Mel). In the rat brain, none of these ligands displayed any type specificity, whereas in guinea pig brain membranes the C-terminally modified peptide, Tyr-Gly-Gly-Phe-Met-Arg-Mel ([Mel7]peptide), displayed a kappa-binding profile and was a weak kappa-opioid-receptor agonist in isolated guinea pig ileum. The effect of sodium ions on [Mel7]peptide competition against [3H]naloxone binding indicated a weak agonist nature of the compound. When guinea pig brain membranes were preincubated with 1-10 microM of [Mel7]peptide, an apparently irreversible inhibition of [3H]naloxone ligand binding was observed. These results suggest that the heptapeptide containing melphalan at the C-terminus can be used as a relatively high-affinity irreversible label for the kappa-opioid receptor.
Sartania
N
N
Institute of Biochemistry, Biological Research Center, Hungarian Academy of Sciences, Szeged.
Szatmári
I
I
Orosz
G
G
Rónai
A Z
AZ
Medzihradszky
K
K
Borsodi
A
A
Benyhe
S
S
D000345:Affinity Labels; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive / Q000187:drug effects; D001921:Brain / Q000378:metabolism; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000378:metabolism; D005260:Female; D006168:Guinea Pigs; D008297:Male; D008558:Melphalan / Q000737:chemistry*; D008566:Membranes / Q000378:metabolism; D009270:Naloxone / Q000494:pharmacology; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D011869:Radioligand Assay; D051381:Rats; D011957:Receptors, Opioid / Q000737:chemistry / Q000378:metabolism*
D000345:Affinity Labels; D009292:Narcotic Antagonists; D011957:Receptors, Opioid; D009270:Naloxone; C051844:norbinaltorphimine; D004744:Enkephalin, Methionine; D009271:Naltrexone; C027511:enkephalin-Met, Arg(6)-Phe(7)-; D008558:Melphalan