NADH-Dependent Inhibition of Branched-Chain Fatty Acid Synthesis in<i>Bacillus subtilis</i>

  • OKU Hirosuke
    Laboratory of Applied Biochemistry, Faculty of Agriculture, University of The Ryukyus
  • FUJITA Keisuke
    Laboratory of Applied Biochemistry, Faculty of Agriculture, University of The Ryukyus
  • NOMOTO Tomoko
    Laboratory of Applied Biochemistry, Faculty of Agriculture, University of The Ryukyus
  • SUZUKI Kiyoshi
    Laboratory of Applied Biochemistry, Faculty of Agriculture, University of The Ryukyus
  • IWASAKI Hironori
    Laboratory of Applied Biochemistry, Faculty of Agriculture, University of The Ryukyus
  • CHINEN Isao
    Laboratory of Applied Biochemistry, Faculty of Agriculture, University of The Ryukyus

書誌事項

タイトル別名
  • NADH-Dependent Inhibition of Branched-Chain Fatty Acid Synthesis in Bacillus subtilis.
  • NADH-Dependent Inhibition of Branched-C

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説明

   Addition of NADH to crude but not to pure branched-chain α-keto acid decarboxylase decreased the CO2 production from α-keto-β-methylvalerate (KMV) suggesting the presence of an NADH dependent inhibitor in the crude enzyme from Bacillus subtilis. This NADH-dependent decarboxylase inhibitor was purified to homogeneity by a fast protein liquid chromatography system.<br>   The purified inhibitor was identical with leucine dehydrogenase as to N-terminal amino acid squence (35 residues) and molecular weight, and catalyzed the oxidative deamination of three branched chain amino acids (BCAAs), valine, leucine, and isoleucine. The decarboxylase inhibitor was therefore identified as leucine dehydrogenase. A decreased substrate availability caused by leucine dehydrogenase thus reasonably accounted for the NADH dependent inhibition of the decarboxylation. In turn, the observation that leucine dehydrogenase competes with the decarboxylase for branched-chain α-keto acid (BCKA) suggested an involvement of this enzyme in the branched chain fatty acid (BCFA) biosynthesis. This view was supported by the observation that addition of NAD to crude fatty acid synthetase increased the incorporation of isoleucine into BCFAs. Pyridoxal-5′-phosphate and α-ketoglutarate, cofactors for BCAA transaminase, modulated BCFA biosynthesis from isoleucine in vitro, suggesting also the involvement of transaminase reaction in BCFA biosynthesis.<br>

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