PMID:14702302
| Citation |
Koyanagi, T, Katayama, T, Suzuki, H and Kumagai, H (2004) Identification of the LIV-I/LS system as the third phenylalanine transporter in Escherichia coli K-12. J. Bacteriol. 186:343-50 |
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| Abstract |
In Escherichia coli, the active transport of phenylalanine is considered to be performed by two different systems, AroP and PheP. However, a low level of accumulation of phenylalanine was observed in an aromatic amino acid transporter-deficient E. coli strain (DeltaaroP DeltapheP Deltamtr Deltatna DeltatyrP). The uptake of phenylalanine by this strain was significantly inhibited in the presence of branched-chain amino acids. Genetic analysis and transport studies revealed that the LIV-I/LS system, which is a branched-chain amino acid transporter consisting of two periplasmic binding proteins, the LIV-binding protein (LIV-I system) and LS-binding protein (LS system), and membrane components, LivHMGF, is involved in phenylalanine accumulation in E. coli cells. The K(m) values for phenylalanine in the LIV-I and LS systems were determined to be 19 and 30 micro M, respectively. Competitive inhibition of phenylalanine uptake by isoleucine, leucine, and valine was observed for the LIV-I system and, surprisingly, also for the LS system, which has been assumed to be leucine specific on the basis of the results of binding studies with the purified LS-binding protein. We found that the LS system is capable of transporting isoleucine and valine with affinity comparable to that for leucine and that the LIV-I system is able to transport tyrosine with affinity lower than that seen with other substrates. The physiological importance of the LIV-I/LS system for phenylalanine accumulation was revealed in the growth of phenylalanine-auxotrophic E. coli strains under various conditions. |
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| Keywords |
Amino Acid Transport Systems; Amino Acid Transport Systems, Neutral/physiology; Bacterial Proteins/physiology; Base Sequence; Biological Transport; Carrier Proteins/analysis; Carrier Proteins/physiology; Escherichia coli/metabolism; Escherichia coli Proteins/physiology; Kinetics; Molecular Sequence Data; Phenylalanine/metabolism |
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