INHIBITION OF ECDYSONE BIOSYNTHESIS IN FLIES BY A HEXAPEPTIDE ISOLATED FROM VITELLOGENIC OVARIES

The only identified insect peptides known to be involved in controllin g the biosynthesis of ecdysone, the steroid moulting hormone of arthro pods, are the prothoracicotropic hormones (PTTH). These neuropeptides stimulate ecdysone biosynthesis. Recently, a hexapeptide (NPTNLH) with folliculostatic and trypsin modulating activity was isolated from vit ellogenic ovaries of the fleshfly Neobellieria bullata. Here we report that the hexapeptide, when tested in vitro on the isolated ring gland of flies, inhibited ecdysone biosynthesis immediately and completely (EC(50) = 5 nM). The hexapeptide is the first known factor with 'proth oracicostatic activity' and may form part of the endocrine system that controls ecdysone biosynthesis in vivo.