[Hyp3]Met-callatostatin. Identification and biological properties of a novel neuropeptide from the blowfly Calliphora vomitoria.

A novel, hydroxyproline-containing neuropeptide, Gly-Pro-Hyp-Tyr-Asp-Phe-Gly-Met-NH2, designated [HYP3]Met-callatostatin, has been identified from extracts of heads of the blowfly Calliphora vomitoria. The peptide is a naturally occurring hydroxylate analogue of Met-callatostatin, a previously identified allatostatin-like peptide, and is present to the extent of 20% of the nonhydroxylated form. In bioassays, both forms of the peptide show allatostatic activity by inhibiting juvenile hormone synthesis and release in the cockroaches Periplaneta americana, Diploptera punctata, and Blattella germanica (IC50 = 100 pM-10 nM). They do not, however, influence juvenile hormone bisepoxide synthesis and release in the blowfly. In flies, [Hyp3]Met-callatostatin inhibits the peristaltic movements of the hindgut, showing a biphasic response (IC50 = 0.5 pM and 0.5 microM) compared with the monophasic response of Met-callatostatin (IC50 = 100 nM). Immunocytochemical studies with Met-callatostatin antisera provide the cytological basis for a myoinhibitory role in the gut since the axons of immunoreactive neurons in the abdominal ganglion project to the ileum. There are also endocrine cells in the midgut that, by releasing the peptides into the hemolymph, would allow the Met-callatostatins to fulfill a neurohormonal role on muscles of the gut and heart. In contrast, there are no Met-callatostatin neural pathways from the brain to the corpus allatum, the gland that produces juvenile hormone. NH2-terminal degradation of Met-callatostatins incubated with the hemolymph of P. americana results in cleavage of the Pro-Tyr bond giving the pentapeptide Tyr-Asp-Phe-Gly-Met-NH2 as a degradation product. In contrast, the Hyp-Tyr bond resists cleavage. With hemolymph from C. vomitoria, no immunoassayable degradation product has been observed with either peptide.