title: Remnants of an ancient pathway to L-phenylalanine and L-tyrosine in enteric bacteria: evolutionary implications and biotechnological impact.
abstract: The pathway construction for biosynthesis of aromatic amino acids in Escherichia coli is atypical of the phylogenetic subdivision of gram-negative bacteria to which it belongs (R. A. Jensen, Mol. Biol. Evol. 2:92-108, 1985). Related organisms possess second pathways to phenylalanine and tyrosine which depend upon the expression of a monofunctional chorismate mutase (CM-F) and cyclohexadienyl dehydratase (CDT). Some enteric bacteria, unlike E. coli, possess either CM-F or CDT. These essentially cryptic remnants of an ancestral pathway can be a latent source of biochemical potential under certain conditions. As one example of advantageous biochemical potential, the presence of CM-F in Salmonella typhimurium increases the capacity for prephenate accumulation in a tyrA auxotroph. We report the finding that a significant fraction of the latter prephenate is transaminated to L-arogenate. The tyrA19 mutant is now the organism of choice for isolation of L-arogenate, uncomplicated by the presence of other cyclohexadienyl products coaccumulated by a Neurospora crassa mutant that had previously served as the prime biological source of L-arogenate. Prephenate aminotransferase activity was not conferred by a discrete enzyme, but rather was found to be synonymous with the combined activities of aspartate aminotransferase (aspC), aromatic aminotransferase (tyrB), and branched-chain aminotransferase (ilvE). This conclusion was confirmed by results obtained with combinations of aspC-, tyrB-, and ilvE-deficient mutations in E. coli. An example of disadvantageous biochemical potential is the presence of a cryptic CDT in Klebsiella pneumoniae, where a mutant carrying multiple enzyme blocks is the standard organism used for accumulation and isolation of chorismate.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Microbiology and Cell Science, University of Florida, Gainesville 32611-0100.
authors.forename: C A
authors.initials: CA
authors.lastname: Bonner
authors.forename: R S
authors.initials: RS
authors.lastname: Fischer
authors.forename: S
authors.initials: S
authors.lastname: Ahmad
authors.forename: R A
authors.initials: RA
authors.lastname: Jensen
mesh_terms: D000600:Amino Acids, Dicarboxylic / Q000378:metabolism; D005075:Biological Evolution; D002851:Chromatography, High Pressure Liquid; D003509:Cyclohexanecarboxylic Acids / Q000378:metabolism; D053138:Cyclohexenes; D004926:Escherichia coli / Q000201:enzymology / Q000378:metabolism*; D007711:Klebsiella pneumoniae / Q000378:metabolism*; D010649:Phenylalanine / Q000096:biosynthesis*; D012486:Salmonella typhimurium / Q000201:enzymology / Q000378:metabolism*; D000637:Transaminases / Q000032:analysis; D014443:Tyrosine / Q000031:analogs & derivatives / Q000096:biosynthesis* / Q000378:metabolism
chemical_list: D000600:Amino Acids, Dicarboxylic; D003509:Cyclohexanecarboxylic Acids; D053138:Cyclohexenes; D014443:Tyrosine; D010649:Phenylalanine; C015478:pretyrosine; D000637:Transaminases; C044954:prephenate aminotransferase; C005550:prephenic acid