PARTIAL CHARACTERIZATION OF ALLATINHIBIN, A NEUROHORMONE OF MANDUCA-SEXTA

During the last larval stage, corpora allata (CA) of Manduca sexta are inactivated by a factor from the brain. Apparently the same factor (a llatinhibin, Al) is secreted by day 4 Vth instar brains kept overnight in Grace's medium. Al is rapidly inactivated by heat or acid but with stands exposure to alkali and can be recovered after freezing and lyop hilization. Exposure to pronase, chymotrypsin, carboxypeptidases-A and -Y, as well as leucine aminopeptidase eliminated Al activity complete ly, whereas after exposure to trypsin and protease XVII-S, some residu al activity remained. Inactivation by pyroglutamate aminopeptidase is interpreted as being due to prolinase activity of this enzyme. Incubat ion of CA with gentamicin, an aminoglycoside antibiotic, affects neith er their ability to produce JH in vitro nor their viability in implant ation assays. However, Al did not inactivate CA in the presence of low concentrations of gentamicin. This effect was used to guard against f alse positive assay results possibly produced by allatotoxic contamina tion. Al was purified by chromatography on Sephadex G-25. All activity recovered emerged from the columns in intermediate fractions with an apparent Mr of 1,000-2,000. (C) 1993 Wiley-Liss, Inc.