This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Guardiola, J. Articles by Iaccarino, M. Search for Related Content PubMed PubMed Citation Articles by Guardiola, J. Articles by Iaccarino, M.

 Previous Article  |  Next Article 

J Bacteriol. 1974 February; 117(2): 382-392
Copyright © 1974 American Society for Microbiology. All Rights Reserved.

Multiplicity of Isoleucine, Leucine, and Valine Transport Systems in Escherichia coli K-12

¹ International Institute of Genetics and Biophysics, C.N.R., 80125 Naples, Italy

ABSTRACT

The kinetics of isoleucine, leucine, and valine transport in Escherichia coli K-12 has been analyzed as a function of substrate concentration. Such analysis permits an operational definition of several transport systems having different affinities for their substrates. The identification of these transport systems was made possible by experiments on specific mutants whose isolation and characterization is described elsewhere. The transport process with highest affinity was called the "very-high-affinity"process. Isoleucine, leucine, and valine are substrates of this transport process and their apparent K_m values are either 10^–8, 2 x 10^–8, or 10^–7 M, respectively. Methionine, threonine, and alanine inhibit this transport process, probably because they are also substrates. The very-high-affinity transport process is absent when bacteria are grown in the presence of methionine, and this is due to a specific repression. Methionine and alanine were also found to affect the pool size of isoleucine and valine. Another transport process is the "high-affinity" process. Isoleucine, leucine, and valine are substrates of this transport process, and their apparent K_m value is 2 x 10^–6 M for all three. Methionine and alanine cause very little or no inhibition, whereas threonine appears to be a weak inhibitor. Several structural analogues of the branched-chain amino acids inhibit the very-high-affinity or the high-affinity transport process in a specific way, and this confirms their existence as two separate entities. Three different "low-affinity" transport processes, each specific for either isoleucine or leucine or valine, show apparent K_m values of 0.5 x 10^–4 M. These transport processes show a very high substrate specificity since no inhibitor was found among other amino acids or among many branched-chain amino acid precursors or analogues tried. The evolutionary significance of the observed redundancy of transport systems is discussed.

This article has been cited by other articles:

• Braun, P. R., Al-Younes, H., Gussmann, J., Klein, J., Schneider, E., Meyer, T. F. (2008). Competitive Inhibition of Amino Acid Uptake Suppresses Chlamydial Growth: Involvement of the Chlamydial Amino Acid Transporter BrnQ. J. Bacteriol. 190: 1822-1830 [Abstract] [Full Text]  
• Rapp, P. (2001). Multiphasic Kinetics of Transformation of 1,2,4-Trichlorobenzene at Nano- and Micromolar Concentrations by Burkholderia sp. Strain PS14. Appl. Environ. Microbiol. 67: 3496-3500 [Abstract] [Full Text]