title: Investigation of receptor binding and functional characteristics of hemopressin(1-7).
abstract: The orally active, α-hemoglobin derived hemopressin (PVNFKFLSH, Hp(1-9)) and its truncated (PVNFKFL, Hp(1-7) and PVNFKF, Hp(1-6)) and extended ((R)VDPVNFKFLSH, VD-Hp(1-9) and RVD-Hp(1-9)) derivatives have been postulated to be the endogenous peptide ligands of the cannabinoid receptor type 1 (CB1). In an attempt to create a versatile peptidic research tool for the direct study of the CB1 receptor-peptide ligand interactions, Hp(1-7) was radiolabeled and in vitro characterized in rat and CB1 knockout mouse brain membrane homogenates. In saturation and competition radioligand binding studies, [(3)H]Hp(1-7) labeled membrane receptors with high densities and displayed specific binding to a receptor protein, but seemingly not to the cannabinoid type 1, in comparison the results with the prototypic JWH-018, AM251, rimonabant, Hp(1-9) and RVD-Hp(1-9) (pepcan 12) ligands in both rat brain and CB1 knockout mouse brain homogenates. Furthermore, functional [(35)S]GTP γS binding studies revealed that Hp(1-7) and Hp(1-9) only weakly activated G-proteins in both brain membrane homogenates. Based on our findings and the latest literature data, we assume that the Hp(1-7) peptide fragment may be an allosteric ligand or indirect regulator of the endocannabinoid system rather than an endogenous ligand of the CB1 receptor.
authors.affiliation: Laboratory of Chemical Biology, Institute of Biochemistry, Biological Research Centre of the Hungarian Academy of Sciences, Szeged, Hungary.
authors.forename: Szabolcs
authors.initials: S
authors.lastname: Dvorácskó
authors.affiliation: Laboratory of Chemical Biology, Institute of Biochemistry, Biological Research Centre of the Hungarian Academy of Sciences, Szeged, Hungary.
authors.forename: Csaba
authors.initials: C
authors.lastname: Tömböly
authors.affiliation: Department of Medical Chemistry, University of Szeged, Szeged, Hungary.
authors.forename: Róbert
authors.initials: R
authors.lastname: Berkecz
authors.affiliation: Laboratory of Chemical Biology, Institute of Biochemistry, Biological Research Centre of the Hungarian Academy of Sciences, Szeged, Hungary. Electronic address: keratti@brc.hu.
authors.forename: Attila
authors.initials: A
authors.lastname: Keresztes
mesh_terms: D000494:Allosteric Regulation; D000818:Animals; D001921:Brain / Q000000981:diagnostic imaging / Q000378:metabolism*; D006454:Hemoglobins / Q000138:chemical synthesis / Q000493:pharmacokinetics*; D008024:Ligands; D051379:Mice; D018345:Mice, Knockout; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000493:pharmacokinetics*; D011485:Protein Binding; D011869:Radioligand Assay; D051381:Rats; D043884:Receptor, Cannabinoid, CB1 / Q000235:genetics / Q000378:metabolism*; D014316:Tritium / Q000493:pharmacokinetics
chemical_list: D006454:Hemoglobins; D008024:Ligands; D010446:Peptide Fragments; D043884:Receptor, Cannabinoid, CB1; C473218:hemopressin; D014316:Tritium
keywords: Cannabinoid receptor; Hemopressin; Ligand stimulated [(35)S]GTPγS binding assay; Radioligand binding assay; Tritium labeling