Sources of propionate for the biogenesis of ethyl-branched insect juvenile hormones: Role of isoleucine and valine

Abstract

Corpora allata from adult female Manduca sexta biosynthesize the sesquiterpenoid juvenile hormone (JH) III and the unusual ethyl-branched homologue JH U in vitro. We maintained corpora allata in medium 199 using [methyl-3ll1methionine as the source of the JH methyl ester moiety and as a mass marker. This allowed measurement of the relative contributions of '4C-labeled precursors to the biogenesis of JH II and III carbon skeletons. We showed efficient incorporation of a propionate equivalent, from isoleucine or valine catabolism, into the ethyl-branched portion of JH II, using doublelabel liquid scintillation counting of isolated JHs and gas chromatography/mass spectrometry with selected ion monitoring of JH deuteromethoxyhydrin derivatives. Methionine was a poor source of propionate for JH II biosynthesis, while glucose, succinate, threonine, and f8-alanine did not contribute propionate at all. Leucine, isoleucine, and glucose incorporated into JH III and the acetate-derived portion of JH II.Of the known insect juvenile hormones (JHs; Fig. 1 (6). Additional studies with corpora allata (the glands that produce JH) homogenates or whole glands demonstrated the biogenesis of important intermediates (7-10) and 4-Me JH I (11). However, no progress has been made in elucidating the regulatory processes that destine an insect to produce only JH III vs. ethyl-branched JH homologues or both. As propionyl-CoA is crucial for the biosynthesis of ethyl-branched JHs, the metabolic control of this precursor may govern the identity of the JH produced. Thus, it is important to determine which specific biochemical pathway contributes propionyl-CoA for ethyl-branched JH biosynthesis.We examined various amino acids, succinate, and glucose as possible sources of propionyl-CoA. An important consideration in the design of this study was the evidence from prior studies with Manduca sexta corpora allata (3) were added as appropriate to provide a fully reconstituted medium. To improve buffering capacity, the concentrations of KH2PO4 and Na2HPO4 were increased to 8.0 mM and 6.0 mM, respectively.Methods. M. sexta were reared as described (14) and the corpora cardiaca-corpora allata (CC-CA) complexes were obtained (15) from adult females 0-16 hr old.Sixteen CC-CA were used for each experiment. These were incubated with vigorous shaking for 1 hr at 28°C in minimal medium containing 100 ,uM L-[methyl-3Hlmethio-nine (1 Ci/mmol), four CC-CA per 100 ,u1. The preincubation depletes endogenous precursors of JH and equilibrates the CC-CA with labeled methionine that serves as mass marker for JH quantification (3). Each group offour CC-CA was then transferred into 100 p.l of fully reconstituted medium containing 100 ,uM L-[methyl-3H]methionine (1 Ci/mmol) and the 14C precursor for study at a concentration equivalent to the unlabeled compound in medium 199. We also studied radiolabeled succinate and f3-alanine (normally not present in medium 199) each at 1 mM. After 4 hr of incubation in the double-labeled medium, JHs were extracted (three tim...

Metabolism of propionic acid to a novel acyl-coenzyme A thioester by mammalian cell lines and platelets

“…Understanding of propionate metabolism has been driven not only by human disease but also by the critical nature of propionate for branched chain hydrocarbons and hormones in insects ( 6,30 ). In fact, 2-methyl-2-pentenoic acid is an aggregation pheromone of the grain borer, and is produced by the grain borer when feeding ( 31 ).…”

Characterization and tissue‐specific expression of two lepidopteran farnesyl diphosphate synthase homologs: Implications for the biosynthesis of ethyl‐substituted juvenile hormones

“…JH is produced by a pair of minute endocrine glands known as the corpora allata (CA). Within the lepidopteran CA, propionyl‐CoA is derived primarily from the metabolism of the branched‐chain amino acids (BCAA) isoleucine and valine 6. BCAA transaminase catalyzes the first step of this conversion 7.…”

Can Juvenile Hormone Research Help Rejuvenate Integrated Pest Management?

“…Biosynthesis of JH proceeds through the mevalonate pathway, whose end product is cholesterol in most other animals, and thus uses acetyl-CoA as the principal building block. In the case of JHs with ethyl side chains, one unit of propionyl-CoA, derived from valine and isoleucine (Brindle et al 1987), substitutes for one of the three acetyl-CoA units that make up mevalonate (Fig. 2).…”