Isoleucine degradation (WP178)

Saccharomyces cerevisiae

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,


Jessica Heckman , Daniela Digles , Egon Willighagen , and Eric Weitz


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Saccharomyces cerevisiae



Pathway Ontology

isoleucine degradation pathway


Label Type Compact URI Comment
L-glutamate Metabolite cas:56-86-0
BAT1 GeneProduct sgd:S000001251
BAT2 GeneProduct sgd:S000003909
PDC1 GeneProduct sgd:S000004034
PDC5 GeneProduct sgd:S000004124
PDC6 GeneProduct sgd:S000003319
ARO10 GeneProduct sgd:S000002788
THI3 GeneProduct sgd:S000002238


  1. Two yeast homologs of ECA39, a target for c-Myc regulation, code for cytosolic and mitochondrial branched-chain amino acid aminotransferases. Eden A, Simchen G, Benvenisty N. J Biol Chem. 1996 Aug 23;271(34):20242–5. PubMed Europe PMC Scholia
  2. Mitochondrial and cytosolic branched-chain amino acid transaminases from yeast, homologs of the myc oncogene-regulated Eca39 protein. Kispal G, Steiner H, Court DA, Rolinski B, Lill R. J Biol Chem. 1996 Oct 4;271(40):24458–64. PubMed Europe PMC Scholia
  3. An investigation of the metabolism of isoleucine to active Amyl alcohol in Saccharomyces cerevisiae. Dickinson JR, Harrison SJ, Dickinson JA, Hewlins MJ. J Biol Chem. 2000 Apr 14;275(15):10937–42. PubMed Europe PMC Scholia
  4. Branched-chain-amino-acid transaminases of yeast Saccharomyces cerevisiae. Prohl C, Kispal G, Lill R. Methods Enzymol. 2000;324:365–75. PubMed Europe PMC Scholia