Isoleucine Degradation (Saccharomyces cerevisiae)

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While Saccharomyces cerevisiae can use most amino acids as their sole nitrogen source, they can only use a few amino acids as a carbon source to support growth (CITS:[Large86][Cooper82]). This is in contrast to most eukaryotes and some fungi, which can metabolize amino acids completely, utilizing them as sole sources of carbon and nitrogen (CITS:[Stryer88][Large 86]). S. cerevisiae degrade the branched-chain amino acids (iso-leucine, leucine, and valine) and the aromatic amino acids (tryptophan, phenylalanine, and tyrosine) via the Ehrlich pathway (CITS:[Sentheshanmuganathan60][10989420]). This pathway is comprised of the following steps: 1) deamination of the amino acid to the corresponding alpha-keto acid; 2) decarboxylation of the resulting alpha-keto acid to the respective aldehyde; and, 3) reduction of the aldehyde to form the corresponding long chain or complex alcohol, known as a fusel alcohol or fusel oil (CITS:[10989420][Large 86]). Fusel alcohols are important flavor and aroma compounds in yeast-fermented food products and beverages (as reported in (CITS:[9546164]) Each of the three steps in branched-chain amino acid degradation can be catalyzed by more than one isozyme; which enzyme is used appears to depend on the amino acid, the carbon source and the stage of growth of the culture (CITS:[12499363]). The initial transamination step in iso-leucine degradation can be catalyzed by either of the branched-chain amino acid transaminases BAT1 (mitochondrial) or BAT2 (cytosolic) (CITS:[10989445][8798704][8702755]). The subsequent decarboxylation step can be catalyzed by any one of the five decarboxylases (Pdc1p, Pdc5p, Pdc6p, Thi3p, and Aro10p) (CITS:[9546164][10753893]) and the final step can be catalyzed by any one of six alcohol dehydrogenases (Adh1p, Adh2p, Adh3p, Adh4p, Adh5p, and Sfa1p) (CITS:[12499363]). SOURCE: SGD pathways,


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  1. Prohl C, Kispal G, Lill R; ''Branched-chain-amino-acid transaminases of yeast Saccharomyces cerevisiae.''; Methods Enzymol, 2000 PubMed Europe PMC Scholia
  2. Eden A, Simchen G, Benvenisty N; ''Two yeast homologs of ECA39, a target for c-Myc regulation, code for cytosolic and mitochondrial branched-chain amino acid aminotransferases.''; J Biol Chem, 1996 PubMed Europe PMC Scholia
  3. Kispal G, Steiner H, Court DA, Rolinski B, Lill R; ''Mitochondrial and cytosolic branched-chain amino acid transaminases from yeast, homologs of the myc oncogene-regulated Eca39 protein.''; J Biol Chem, 1996 PubMed Europe PMC Scholia
  4. Dickinson JR, Harrison SJ, Dickinson JA, Hewlins MJ; ''An investigation of the metabolism of isoleucine to active Amyl alcohol in Saccharomyces cerevisiae.''; J Biol Chem, 2000 PubMed Europe PMC Scholia


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69780view12:40, 11 July 2013Egonw
69646view20:37, 8 July 2013MaintBotUpdated to 2013 gpml schema
67417view10:58, 26 June 2013DdiglesOntology Term : 'isoleucine degradation pathway ' added !
41884view04:52, 2 March 2011MaintBotRemoved redundant pathway information and comments
36611view22:30, 9 April 2010MaintBotDescription and bibliography added from SGD
21053view11:30, 14 November 2008MaintBot[[Pathway:Saccharomyces cerevisiae:Isoleucine Degradation]] moved to [[Pathway:WP178]]: Moved to stable identifier
12754view08:01, 17 May 2008MaintBotautomated metabolite conversion
8792view14:09, 7 January 2008MaintBotAdded to category $category
8790view14:09, 7 January 2008J.HeckmanUploaded new pathway

External references


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NameTypeDatabase referenceComment
ARO10GeneProductS000002788 (SGD)
BAT1GeneProductS000001251 (SGD)
BAT2GeneProductS000003909 (SGD)
L-glutamateMetabolite56-86-0 (CAS)
PDC1GeneProductS000004034 (SGD)
PDC5GeneProductS000004124 (SGD)
PDC6GeneProductS000003319 (SGD)
THI3GeneProductS000002238 (SGD)

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