Comparative metabolism of branched-chain amino acids to precursors of juvenile hormone biogenesis in corpora allata of lepidopterous versus nonlepidopterous insects.
Comparative studies were performed on the role of branched-chain amino acids (BCAA) in juvenile hormone (JH) biosynthesis using several lepidopterous and nonlepidopterous insects. Corpora cardiaca-corpora allata complexes (CC-CA, the corpora allata being the organ of JH biogenesis) were maintained in culture medium containing a uniformly 14C-labeled BCAA, together with [methyl-3H]methionine as mass marker for JH quantification. BCAA catabolism was quantified by directly analyzing the medium for the presence of 14C-labeled propionate and/or acetate, while JHs were extracted, purified by liquid chromatography, and subjected to double-label liquid scintillation counting. Our results indicate that active BCAA catabolism occurs within the CC-CA of lepidopterans, and this efficiently provides propionyl-CoA (from isoleucine or valine) for the biosynthesis of the ethyl branches of JH I and II. Acetyl-CoA, formed from isoleucine or leucine catabolism, is also utilized by lepidopteran CC-CA for biosynthesizing JH III and the acetate-derived portions of the ethyl-branched JHs. In contrast, CC-CA of nonlepidopterans fail to catabolize BCAA. Consequently, exogenous isoleucine or leucine does not serve as a carbon source for the biosynthesis of JH III by these glands, and no propionyl-CoA is produced for genesis of ethyl-branched JHs. This is the first observation of a tissue-specific metabolic difference which in part explains why these novel homosesquiterpenoids exist in lepidopterans, but not in nonlepidopterans.
Brindle
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Zoecon Research Institute, Sandoz Crop Protection, Palo Alto, California 94304.
Schooley
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Tsai
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Baker
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D000597:Amino Acids, Branched-Chain / Q000378:metabolism*; D000818:Animals; D002250:Carbon Radioisotopes; D007313:Insecta / Q000378:metabolism*; D007532:Isoleucine / Q000378:metabolism; D007605:Juvenile Hormones / Q000096:biosynthesis*; D007915:Lepidoptera / Q000378:metabolism*; D007930:Leucine / Q000378:metabolism; D008715:Methionine / Q000378:metabolism; D013045:Species Specificity; D014316:Tritium
D000597:Amino Acids, Branched-Chain; D002250:Carbon Radioisotopes; D007605:Juvenile Hormones; D007532:Isoleucine; D014316:Tritium; D008715:Methionine; D007930:Leucine