Tryptophan degradation (WP301)

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 aromatic amino acids (tryptophan, phenylalanine, and tyrosine) and the branched-chain amino acids (valine, leucine, and iso-leucine) 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]). The primary aminotransferase in tryptophan degradation is postulated to be Aro9p (CITS:[6763508]). In vitro studies demonstrated that Aro9p is active with phenylpyruvate, pyruvate, or p-hydroxyphenylpyruvate, but not 2-oxoglutarate as the amino acceptor (CITS:[6763508]). Aro9p is induced by aromatic amino acids and is subject to nitrogen regulation (CITS:[6763508][10207060]). The decarboxylase encoding gene ARO10 appears to be transcriptionally regulated in a similar fashion(CITS:[10207060]). Gap1p, a general amino acid permease, and Wap1p, an inducible amino acid permease with wide substrate specificity, appear to be the main uptake systems for utilizing aromatic amino acids (CITS:[10207060]). SOURCE: SGD pathways,


Meredith Braymer , Thomas Kelder , Egon Willighagen , Alex Pico , Daniela Digles , Friederike Ehrhart , and Eric Weitz


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Saccharomyces cerevisiae



Pathway Ontology

tryptophan degradation pathway


Label Type Compact URI Comment
CO2 Metabolite chebi:16526
2-oxoglutarate Metabolite chebi:16810
Phenylpyruvate Metabolite chebi:30851
Indolepyruvate Metabolite hmdb:HMDB0060484
L-tryptophan Metabolite cas:73-22-3
L-glutamate Metabolite cas:56-86-0
Indole-3-ethanol Metabolite chebi:17890
Indoleacetaldehyde Metabolite chebi:18086
NAD Metabolite hmdb:HMDB0000902
L-phenylalanine Metabolite cas:63-91-2
NADH Metabolite cas:53-84-9
ADH1 GeneProduct sgd:S000005446
ADH5 GeneProduct sgd:S000000349
PDC1 GeneProduct sgd:S000004034
ARO8 GeneProduct ensembl:YGL202W
PDC5 GeneProduct sgd:S000004124
ARO9 GeneProduct ensembl:YHR137W
PDC6 GeneProduct sgd:S000003319
SFA1 GeneProduct sgd:S000002327
ADH2 GeneProduct sgd:S000004918
ADH4 GeneProduct sgd:S000003225
ADH3 GeneProduct sgd:S000004688
ARO10 GeneProduct sgd:S000002788


  1. Tryptophan degradation in Saccharomyces cerevisiae: characterization of two aromatic aminotransferases. Kradolfer P, Niederberger P, Hütter R. Arch Microbiol. 1982 Dec 11;133(3):242–8. PubMed Europe PMC Scholia
  2. Phenylalanine- and tyrosine-auxotrophic mutants of Saccharomyces cerevisiae impaired in transamination. Urrestarazu A, Vissers S, Iraqui I, Grenson M. Mol Gen Genet. 1998 Jan;257(2):230–7. PubMed Europe PMC Scholia
  3. Characterisation of Saccharomyces cerevisiae ARO8 and ARO9 genes encoding aromatic aminotransferases I and II reveals a new aminotransferase subfamily. Iraqui I, Vissers S, Cartiaux M, Urrestarazu A. Mol Gen Genet. 1998 Jan;257(2):238–48. PubMed Europe PMC Scholia
  4. The catabolism of amino acids to long chain and complex alcohols in Saccharomyces cerevisiae. Dickinson JR, Salgado LEJ, Hewlins MJE. J Biol Chem. 2003 Mar 7;278(10):8028–34. PubMed Europe PMC Scholia