Phenylalanine biosynthesis (Saccharomyces cerevisiae)

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Biosynthesis of the aromatic amino acids phenylalanine, tyrosine, and tryptophan proceeds via a common pathway to chorismate, at which point the pathway branches (CITS:[Jones][1943992]). One branch proceeds to phenylalanine and tyrosine, and the other to tryptophan (CITS:[Jones]). The phenylalanine and tyrosine branch has one reaction in common, rearrangement of chorismate to prephenate, at which point, the pathway branches again to either phenylalanine or tyrosine (CITS:[1943992])). S. cerevisiae, similar to E. coli, synthesize phenylalanine and tyrosine via the intermediate 4-hydroxyphenylpyruvate and phenylpyruvate, respectively, while some other organisms synthesize them via arogenate (CITS:[1943992]). Aromatic amino acid biosynthesis in S. cerevisiae is controlled by a combination of feedback inhibition, activation of enzyme activity, and regulation of enzyme synthesis (CITS:[Jones][1943992]). The carbon flow through the pathways is regulated primarily at the initial step and the branching points by the terminal end-products. The initial step of chorismate biosynthesis can be catalyzed by two isoenzymes Aro3p or Aro4p, whereby Aro3p is inhibited by phenylalanine, and Aro4p by tyrosine (CITS:[Jones][1943992]). The first step in the phenylalanine-tyrosine branch is feedback inhibited by tyrosine and activated by tryptophan (CITS:[1943992]). The transcriptional activator GCN4 regulates most of the genes encoding for the aromatic amino acid biosynthetic enzymes; however, no GCN4 regulation was found for ARO7 of the phenylalanine and tyrosine and branch, TYR1 of the tyrosine branch, or TRP1 of the tryptophan branch (CITS:[1943992]). SOURCE: SGD pathways, http://pathway.yeastgenome.org/server.html