Structure/Activity Relationships in the Adipokinetic Hormone/Red Pigment Concentrating Hormone Family

Abstract

The structures of 3 locust adipokinetic hormones are known: the decapeptide adipokinetic hormone I is common to all species of locust investigated so far, but the octapeptide AKH-II’s of Locusta (AKH-IIL) and Schistocerca (AKH-IIS) differ by a single amino acid (see Table 1). In addition to these locust peptides, structurally related but often functionally different peptides from other insect species have been sequenced. These include the adipokinetic peptide from Heliothis zea (Jaffe et al., 1986), which is identical to that in Manduca sexta (Ziegler et al., 1985); hypertrehalosaemic peptides I and II from Periplaneta americana (sequenced independently by various groups; see Goldsworthy et al., 1986a); and hypertrehalosaemic factor II from Carausius morosus (Gäde and Rinehart, 1986). Together with a crustacean peptide, Red Pigment Concentrating Hormone, these peptides apparently represent a group of closely related molecules, the AKH/RPCH family: they possess striking sequence and structural similarities, including blocked amino and carboxy terminals. We have compared the activities of these peptides in the locust hyperlipaemic assay to give an insight into the structural features necessary for the fit of the AKH molecule to its receptor on the fat body.