Receptor binding profile of neuropeptide gamma and its fragments: comparison with the nonmammalian peptides carassin and ranakinin at three mammalian tachykinin receptors

The tachykinin binding site preferences of neuropeptide gamma (NP gamma), its C-terminal fragments AcNP gamma(3-21), AcNP gamma(5-21), AcNP gamma(7-21), and AcNP gamma(9-21), other mammalian tachykinins, and the nonmammalian tachykinins ranakinin and carassin were examined in membrane binding competition studies. [125I]-Bolton-Hunter [Sar9,Met(O2)11]SP (BHSarSP), [125I]-neurokinin A (INKA) and [125I]-Bolton-Hunter scyliorhinin II (BHScyII) were used to investigate NK-1, NK-2, and NK-3 sites, in rat submandibular gland, gastric fundus, and brain, respectively. Elongation of the neurokinin A molecule does not appear to influence binding to rat tachykinin NK-1 and NK-2 binding sites. Ranakinin has affinity for the NK-1 and NK-2 site similar to that of substance P and neurokinin A, respectively, but has low affinity for the NK-3 site. Despite its structural similarities to neuropeptide gamma, carassin has only moderate affinity for rat tachykinin binding sites. Possession of an acidic residue at position 4 appears critical for binding to rat NK-2 sites.