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If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Synonyms: trp degradation, Ehrlich pathway, fusel alcohol biosynthesis, indole-3-ethanol biosynthesis
| Superclasses: | Degradation/Utilization/Assimilation → Amino Acid Degradation → Proteinogenic Amino Acid Degradation → L-tryptophan Degradation |
Summary:
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
[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
[Stryer88,
Large86]. 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
[Sentheshanmugan60,
Dickinson00]. 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
[Dickinson00,
Large86]. Fusel alcohols are important flavor and aroma compounds in yeast-fermented food products and beverages (as reported in
[terSchure98].
The primary aminotransferase in tryptophan degradation is postulated to be Aro9p [Kradolfer82]. In vitro studies demonstrated that Aro9p is active with phenylpyruvate, pyruvate, or p-hydroxyphenylpyruvate, but not 2-oxoglutarate as the amino acceptor [Kradolfer82]. Aro9p is induced by aromatic amino acids and is subject to nitrogen regulation [Kradolfer82, Iraqui99]. The decarboxylase encoding gene ARO10 appears to be transcriptionally regulated in a similar fashion [Iraqui99]. 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 [Iraqui99].
Citations: [Dickinson03, Urrestarazu98, Iraqui98]
Locations of Mapped Genes:
Credits:
Revised 08-May-2008 by
Krieger C,
Saccharomyces Genome Database
Large86: Large PJ (1986). "Degradation of Organic Nitrogen Compounds by Yeasts." Yeast (2) 1-34.
Stryer88: Stryer L (1988). "Biochemistry (3rd ed.)." New York: W. H. Freeman and Company.
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