RECEPTOR-BINDING PROFILE OF NEUROPEPTIDE-GAMMA AND ITS FRAGMENTS - COMPARISON WITH THE NONMAMMALIAN PEPTIDES CARASSIN AND RANAKININ AT 3 MAMMALIAN TACHYKININ RECEPTORS

The tachykinin binding site preferences of neuropeptide gamma (NP-gamm a), its C-terminal fragments AcNPgamma(3-2 1), AcNPgamma(5-2 1), AcNPg amma(7-2 1), and AcNPgamma(9-2 1), other mammalian tachykinins, and th e nonmammalian tachykinins ranakinin and carassin were examined in mem brane binding competition studies. [I-125]-Bolton-Hunter [Sar9,Met(O2) 11]SP (BHSarSP), [I-125]-neurokinin A (INKA) and [I-125]-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, respe ctively. Elongation of the neurokinin A molecule does not appear to in fluence binding to rat tachykinin NK-1 and NK-2 binding sites. Ranakin in has affinity for the NK-1 and NK-2 site similar to that of substanc e P and neurokinin A, respectively, but has low affinity for the NK-3 site. Despite its structural similarities to neuropeptide gamma, caras sin has only moderate affinity for rat tachykinin binding sites. Posse ssion of an acidic residue at position 4 appears critical for binding to rat NK-2 sites.