Phenylalanine degradation (WP573)

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 (phenylalanine, tyrosine, and tryptophan) 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]). Aro10p appears to be the primary decarboxylase catalyzing the second step in phenylalanine degradation (CITS:[12902239][15933030]). Although Vulrahan et. al. (2003) (CITS:[12902239]) found that THI3 does not encode an active phenylpyruvate decarboxylase, they found Thi3p was required in conjunction with one of the pyruvate decarboxylases Pdc1p, Pdc5p or Pdc6p for the ARO10-independent decarboxylase activity. The main uptake systems for utilizing aromatic amino acids appear to be Gap1p, a general amino acid permease, and Wap1p, an inducible amino acid permease with wide substrate specificity (CITS:[10207060]) SOURCE: SGD pathways, http://pathway.yeastgenome.org/server.html

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