The adipokinetic neuropeptide of Mantodea. Sequence elucidation and evolutionary relationships

A neuropeptide with adipokinetic activity in Locusta migratoria and the mantid Empusa pennata, and hypertrehalosaemic activity in Periplaneta americana, was isolated by reversed-phase high performance liquid chromatography from corpora cardiaca of the mantids E. pennata and Sphodromantis sp. After brief enzymatic digestion by 5-oxoprolylpeptidase the primary structure of the peptide of each species was determined by pulsed-liquid phase sequencing employing Edman degradation. The C-terminus of both peptides was blocked, as indicated by the lack of digestion with carboxypeptidase A. The peptides of both species were identical: a blocked, uncharged octapeptide with the sequence L-Glu-Val-Asn-Phe-Thr-Pro-Asn-Trp-NH2. The peptide is now called mantid adipokinetic hormone (Emp-AKH). The synthetic peptide was chromatographically indistinguishable from the natural compound and increased blood lipids in locusts and blood carbohydrates in cockroaches when administered in low doses. The structural features clearly define the peptide as a novel member of the large AKH/RPCH-family of peptides. Seven amino-acid residues are at identical positions in Emp-AKH when compared with the adipokinetic hormone of a dragonfly (Lia-AKH) and the hypertrehalosaemic hormone I from the American cockroach (Pea-CAH-I). Evolutionary relationships to other insect orders are discussed.