Metabolism of Isoleucine to Insect Juvenile Hormone II via Propionyl-Coenzyme A

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It has been shown that isoleucine and valine supply propionate units used specifically for the biosynthesis of the ethyl-branched juvenile hormones (JHs). Insect corpora allata (CA) which do not metabolize them readily (the CA of Lepidoptera) secrete propionate and ethyl-branched JHs. This research will extend these studies and determine what allows the CA to violate the rules of sesquiterpenoid biosynthesis and to incorporate propionyl-CoA into this pathway. The metabolism of ıU-14c! isoleucine will be examined in several tissues of insects which make the ethyl-branched JHs vs. those that produce only JH III. These data are important for interpreting metabolic differences between species. In addition, the metabolism of ıU-14c! isoleucine in isolated mitochondria will also be studied. This work will determine whether or not there is an efficient transport system for exporting propionyl-CoA from the mitochondria. Carnitine propionyl transferase and methyl citrate formation will be examined as likely possibilities for propionyl CoA transport. If this phenomenon cannot be explained by a unique system for propionate transport, the possibility will be investigated that certain enzymes might be located in different subcellular organelles than those in which they are generally held to exist. Juvenile hormones are a group of structurally related compounds secreted by members of the class Insecta and which possess morphogenetic and gonadotropic activity. It is important to have a basic knowledge of the metabolic pathways involved to understand why and how insects are able to synthesize these hormones. Knowledge of the biochemical details of this pathway could point the way towards synthesis of chemicals which specifically inhibit it. These chemicals would be antihormones (and probably, therefore, specific insecticides) to the order of insects that includes moths, which are some of the most damaging of crop pests.