Synthesis of adipokinetic hormone (AKH-I) in the locust brain

Abstract

Methanol extracts of vitellogenic female locust brains contain two factors that inhibit protein synthesis in fat body tissue excised from such individuals. One of these factors (BI) elicits lipid mobilization when injected into adult male locusts. The retention times of BI on an RP-18 column and on an RP-4 column are identical to those of synthetic locust adipokinetic hormone (AKH-I) on each of these columns. Half maximal inhibition of protein synthesis in excised adult locust fat bodies is exerted by 0.05 brain extract equivalents of BI, which is equivalent to activity elicited by 1.5 pmol of AKH-I, as previously determined by AKH-radioimmunoassay. Enzymatic hydrolysis of the N-terminal pyroglutamate, followed by amino acid sequence analysis, indicates that the structure of BI is similar to that of the decapeptide AKH-I synthesized in the glandular lobe of the locust corpora cardiaca (CC). Incorporation of [5-³H]tryptophan into BI of locust brains incubated in vitro indicates that the AKH-I present in the brain is synthesized in situ and is not transported from the CC. Similar incorporation of radiolabel into AKH-I is obtained when excised CC are incubated in vitro.