Tryptophan degradation (WP301)

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, http://pathway.yeastgenome.org/server.html

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