Recognition of neuropeptides FMRFamide and LPLRFamide by chicken cerebellum avian pancreatic polypeptide binding sites.

Binding isotherms were constructed for the binding of synthetic tetrapeptide and pentapeptide fragments to membranes prepared from chicken cerebellar tissue. Both the tetrapeptide (FMRFamide), which was originally isolated from ganglia of mollusks, and the pentapeptide (LPLRFamide) previously isolated from chicken brain are known to increase blood pressure and modulate brain neurons in rats. The C-terminal dipeptide sequences of the two peptides are identical and both show similarity to the dipeptide sequence established for the pancreatic polypeptide (PP) family. Specific high-affinity binding sites exist for the latter peptide, sites which are competed for (though with less affinity) by neuropeptide Y (NPY). Affinity for cerebellar membranes was virtually equivalent for the synthetic peptide LPLRFamide and FRMFamide; the binding affinities (IC50) of all fragments tested (C-terminal pentapeptides of avian PP and NPY, and FMRFamide and LPLRFamide) fell in the same approximate range. Since the N-terminal residues of FMRFamide and LPLRFamide are not homologous with equivalent residues of APP or NPY, our results indicate that only Arg-Tyr-NH2 or Arg-Phe-NH2 sequences are necessary for binding of the carboxy terminus peptides of the PP family. In this respect, these sequences are functionally equivalent.

Binding of C-terminal segments of neuropeptide Y to chicken brain.

The C-terminal pentapeptide amide segment of neuropeptide Y (NPY) binds specifically to chicken brain membrane preparations. The contribution of each residue of the C-terminus to this binding has been investigated through the synthesis and evaluation of a series of pentapeptide analogs. The binding of these molecules is strongly dependent on the presence of certain functional groups, in particular the guanidinium group of Arg-35 and the C-terminal aromatic amide function. The significance of these results for the binding to chicken brain tissue of NPY, pancreatic polypeptide and other potentially related neuropeptides is discussed.