Two novel members of the adipokinetic hormone/red pigment-concentrating hormone family of peptides were identified in dung beetles of the genus Onitis using heterologous (measuring lipid and carbohydrate mobilization in locusts and cockroaches) and a homologous (measuring proline increase in the haemolymph) bioassay(s). Isolation of the peptides was achieved by single-step reverse-phase HPLC of corpora cardiaca extracts. The primary structure was elucidated by automated Edman degradation and by electrospray MS. Both peptides are blocked octapeptides containing three aromatic amino acids. Peptide 1, designated Ona-CC-I, is pGlu-Tyr-Asn-Phe-Ser-Thr-Gly-Trp-NH2, and peptide 2, designated Ona-CC-II, is pGlu-Phe-Asn-Tyr-Ser-Pro-Asp-Trp-NH2. The synthetic peptides were chromatographically indistinguishable from the natural compounds. They both had a hyperprolinaemic effect in the dung beetle. Moreover, flight experiments established that proline is an important fuel to power flight metabolism in Onitis species. Therefore, it is concluded that these novel and unique peptides are involved in regulating proline-based flight metabolism.

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