Distinct sequences of AKH/RPCH family members in beetle (Scarabaeus-species) corpus cardiacum contain three aromatic amino acid residues.

Two forms of AKH/RPCH family peptides have been identified from the corpus cardiacum of various dung beetle species of the genus Scarabaeus and the related genus Gareta by using RP-HPLC. The primary structures were established in two species by automated Edman degradation and mass spectral analysis as blocked octapeptides containing three aromatic amino acids (at positions 2, 4 and 8): peptide I: pGlu-Phe-Asn-Tyr-Ser-Pro-Asp-Trp-NH2; peptide II: pGlu-Phe-Asn-Tyr-Ser-Pro-Val-Trp-NH2. The peptides were not active in the heterologous adipokinetic bioassay in locusts, but increased the concentration of proline in the haemolymph of Scarabaeus beetles. Since proline is also used in these species to provide the energy for contraction of the flight muscles during flight, it is proposed that the distinct peptides characterized here are responsible for the hormonal control of proline homeostasis.