If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Locations of Mapped Genes:
|Superclasses:||Biosynthesis → Amino Acids Biosynthesis → Proteinogenic Amino Acids Biosynthesis → L-tyrosine Biosynthesis|
The pathways of biosynthesis of phenylalanine and tyrosine are intimately connected. The first step of both pathways is the conversion of chorismate to prephenate; the third step of both is the conversion of a ketoacid to the aminoacid through transamination. The two pathways differ only in the second step of their three-step reaction sequences: In the case of phenylalanine biosynthesis a dehydratase converts prephenate to phenylpyruvate (a reaction that occurs slowly in the absence of enzymic acitivity); in the case of tyrosine biosynthesis, a dehydrogenase converts prephenate to p-hydroxyphenylpyruvate. Also in both pathways the first two steps are catalyzed by two distinct active sites on a single protein. Thus the first step of each pathway can be catalyzed by two enzymes: those associated with both the phenylalanine-specific dehydratase and the tyrosine-specific dehydrogenase. Three enzymes, those encoded by tyrB, aspC, and ilvE, are involved in catalyzing the third step of these pathways: all three can contribute to the synthesis of phenylalanine; only TyrB and AspC contribute to the biosynthesis of tyrosine.
Under normal physiological conditions, TyrB is the primary enzyme contributing to the synthesis of tyrosine and phenylalanine. AspC contributes to their synthesis when substrate pools are large. The contribution of the ilvE-encoded enzyme to phenylalanine biosynthesis was demonstrated in triple mutants of Escherichia coli K-12 that lacked all three aminotransferases and required both phenylalanine and tyrosine for growth. However, tyrB and aspC double mutants required only tyrosine for growth [Gelfand77]. This suggested a role for IlvE in phenylalanine biosynthesis in the tyrB, aspC double mutants, although its role in strains with functional TyrB and AspC is unknown.
Review: Pittard, J. and J. Yang (2008) "Biosynthesis of the Aromatic Amino Acids." EcoSal 22.214.171.124 [ECOSAL]
Almo94: Almo SC, Smith DL, Danishefsky AT, Ringe D (1994). "The structural basis for the altered substrate specificity of the R292D active site mutant of aspartate aminotransferase from E. coli." Protein Eng 7(3);405-12. PMID: 7909946
BaezViveros04: Baez-Viveros JL, Osuna J, Hernandez-Chavez G, Soberon X, Bolivar F, Gosset G (2004). "Metabolic engineering and protein directed evolution increase the yield of L-phenylalanine synthesized from glucose in Escherichia coli." Biotechnol Bioeng 87(4);516-24. PMID: 15286989
Baldwin81: Baldwin GS, Davidson BE (1981). "A kinetic and structural comparison of chorismate mutase/prephenate dehydratase from mutant strains of Escherichia coli K 12 defective in the PheA gene." Arch Biochem Biophys 1981;211(1);66-75. PMID: 7030214
Baldwin83: Baldwin GS, Davidson BE (1983). "Kinetic studies on the mechanism of chorismate mutase/prephenate dehydratase from Escherichia coli K12." Biochim Biophys Acta 1983;742(2);374-83. PMID: 6337635
Birolo95: Birolo L, Sandmeier E, Christen P, John RA (1995). "The roles of Tyr70 and Tyr225 in aspartate aminotransferase assessed by analysing the effects of mutations on the multiple reactions of the substrate analogue serine o-sulphate." Eur J Biochem 232(3);859-64. PMID: 7588727
Birolo99: Birolo L, Malashkevich VN, Capitani G, De Luca F, Moretta A, Jansonius JN, Marino G (1999). "Functional and structural analysis of cis-proline mutants of Escherichia coli aspartate aminotransferase." Biochemistry 38(3);905-13. PMID: 9893985
Bonner90a: Bonner CA, Fischer RS, Ahmad S, Jensen RA (1990). "Remnants of an ancient pathway to L-phenylalanine and L-tyrosine in enteric bacteria: evolutionary implications and biotechnological impact." Appl Environ Microbiol 56(12);3741-7. PMID: 2082822
Chao99: Chao YP, Lai ZJ, Chen P, Chern JT (1999). "Enhanced conversion rate of L-phenylalanine by coupling reactions of aminotransferases and phosphoenolpyruvate carboxykinase in Escherichia coli K-12." Biotechnol Prog 15(3);453-8. PMID: 10356262
Chen03: Chen S, Vincent S, Wilson DB, Ganem B (2003). "Mapping of chorismate mutase and prephenate dehydrogenase domains in the Escherichia coli T-protein." Eur J Biochem 270(4);757-63. PMID: 12581215
Cho04: Cho BK, Park HY, Seo JH, Kinnera K, Lee BS, Kim BG (2004). "Enzymatic resolution for the preparation of enantiomerically enriched D-beta-heterocyclic alanine derivatives using Escherichia coli aromatic L-amino acid transaminase." Biotechnol Bioeng 88(4);512-9. PMID: 15459908
Chow04: Chow MA, McElroy KE, Corbett KD, Berger JM, Kirsch JF (2004). "Narrowing substrate specificity in a directly evolved enzyme: the A293D mutant of aspartate aminotransferase." Biochemistry 43(40);12780-7. PMID: 15461450
Collier72: Collier RH, Kohlhaw G (1972). "Nonidentity of the aspartate and the aromatic aminotransferase components of transaminase A in Escherichia coli." J Bacteriol 1972;112(1);365-71. PMID: 4404056
Danishefsky91: Danishefsky AT, Onnufer JJ, Petsko GA, Ringe D (1991). "Activity and structure of the active-site mutants R386Y and R386F of Escherichia coli aspartate aminotransferase." Biochemistry 1991;30(7);1980-5. PMID: 1993208
Davidson72: Davidson BE, Blackburn EH, Dopheide TA (1972). "Chorismate mutase-prephenate dehydratase from Escherichia coli K-12. I. Purification, molecular weight, and amino acid composition." J Biol Chem 247(14);4441-6. PMID: 4557843
Deu07: Deu E, Kirsch JF (2007). "Cofactor-directed reversible denaturation pathways: the cofactor-stabilized Escherichia coli aspartate aminotransferase homodimer unfolds through a pathway that differs from that of the apoenzyme." Biochemistry 46(19);5819-29. PMID: 17441730
Deu09: Deu E, Dhoot J, Kirsch JF (2009). "The partially folded homodimeric intermediate of Escherichia coli aspartate aminotransferase contains a "molten interface" structure." Biochemistry 48(2);433-41. PMID: 19099423
DiazMejia09: Diaz-Mejia JJ, Babu M, Emili A (2009). "Computational and experimental approaches to chart the Escherichia coli cell-envelope-associated proteome and interactome." FEMS Microbiol Rev 33(1);66-97. PMID: 19054114
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