PMID:2082822
| Citation |
Bonner, CA, Fischer, RS, Ahmad, S and 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. 56:3741-7 |
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| 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) |
| Links | |
| Keywords |
Amino Acids, Dicarboxylic/metabolism; Biological Evolution; Chromatography, High Pressure Liquid; Cyclohexanecarboxylic Acids/metabolism; Cyclohexenes; Escherichia coli/enzymology; Escherichia coli/metabolism; Klebsiella pneumoniae/metabolism; Phenylalanine/biosynthesis; Salmonella typhimurium/enzymology; Salmonella typhimurium/metabolism; Transaminases/analysis; Tyrosine/analogs & derivatives; Tyrosine/biosynthesis; Tyrosine/metabolism |
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