Comparison of the biological activities of an insect and a crustacean neurohormone that are structurally similar

Abstract

THE molecular structure of locust adipokinetic hormone (AKH) (ref. 1), closely resembles that of the only other arthropod neurohormone to be fully characterised, prawn red-pigment-concentrating hormone (RPCH) (ref. 2). The first eight residues of the decapeptide, AKH, are homologous with the octapeptide, RPCH, except for threonine instead of serine as residue 5, and asparagine instead of glycine as residue 7, as shown below. Although both hormones are the products of neuroendocrine organs, such close similarities in structure were somewhat unexpected, as the two hormones have completely different physiological actions. AKH in the locust controls lipid utilisation for energy during prolonged flights, by stimulating the release of diglycerides from the fat body³, and regulating their utilisation by the flight muscle⁴. RCPH in the prawn stimulates the concentration of pigment within the red chromatophores⁵. We present here evidence that the two hormones can reproduce each other's effects when cross tested on members of the two arthropod groups.