RRC ID 80713
Author Koyanagi T, Katayama T, Suzuki H, Kumagai H.
Title Identification of the LIV-I/LS system as the third phenylalanine transporter in Escherichia coli K-12.
Journal J Bacteriol
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.
Volume 186(2)
Pages 343-50
Published 2004-1-1
DOI 10.1128/JB.186.2.343-350.2004
PMID 14702302
PMC PMC305776
MeSH 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*
IF 3.006
Prokaryotes E. coli ME9982 ME9983 ME9984 ME9985 ME9986