Canadian Forest Service Publications

Rate of isoleucine metabolism in lepidopteran corpora allata: regulation of the proportion of juvenile hormone homologues released. 1996. Cusson, M.; Le Page, A.; McNeil, J.N.; Tobe, S.S. Insect Biochemistry and Molecular Biology 26: 195-201.

Year: 1996

Issued by: Laurentian Forestry Centre

Catalog ID: 16674

Language: English

Availability: PDF (request by e-mail)

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We tested the hypothesis that shifts in the proportions of the various juvenile hormones (JHs) and precursor acids released by lepidopteran corpora allata (CA) are associated with changes in the activity of enzymes involved in the production of propionate from isoleucine. Measurements of enzyme activity were made on CA of adult Pseudaletia unipuncta, using the assay developed by Brindle et al. [Arch. Insect Biochem. Physiol., 19, 1 (1992)]. Female and male CA of P. unipuncta release the three principal forms of JH and JH acid (JHA), respectively, in proportions that vary according to age and total hormonal output. In addition, female CA incorporate isoleucine-derived propionate into JH I and JH II in a stoichiometric fashion. The branched-chain amino avid (BCAA) transaminase, an enzyme that catalyzes the first step in the conversion of isoleucine into propionate, was 5-25 times more active in homogenates of male CA than in those of females, and its activity increased as a function of age in males but not in females. Similar trends were observed for the accumulation of metabolites produced in later steps of this conversion. These observations support the hypothesis that the age-related increase in the biosynthesis of JHA I by male CA is associated with a rise in the production of propionate, whereas limited availability of propionate in female glands leads to an age-dependent decrease in the proportion of JH I released. These results also imply the existence of a mechanism regulating propionate production in lepidopteran CA. The regulatory factor, however, is not Manduca allatostatin as it had no detectable effect on isoleucine metabolism by either intact male or female CA. Lastly, changing the concentration of acetate and propionate in the CA incubation medium has a greater impact on the proportions of JH I and JH II released than on the proportion of JH III.