Pflügers Archiv

, Volume 445, Issue 5, pp 529–533 | Cite as

System L: heteromeric exchangers of large, neutral amino acids involved in directional transport

  • François Verrey
Frontiers in Physiology


The plasma membrane transport system L is in many cells the only (efficient) pathway for the import of large branched and aromatic neutral amino acids. The corresponding transporters are hetero(di)mers composed of a catalytic subunit (LAT1 or LAT2=light chain=glycoprotein-associated amino acid transporter) associated covalently with the glycoprotein 4F2hc/CD98 (heavy chain). The tissue distribution of LAT1 suggests that it is involved mainly in transporting amino acids into growing cells and across some endothelial/epithelial secretory barriers, whereas the localization of LAT2 indicates that it is mainly involved in the basolateral efflux step of transepithelial (re)absorptive amino acid transport. However, system L transporters are obligatory amino acid exchangers with 1:1 stoichiometry, with similar (but not identical) intra- and extracellular substrate selectivities and with highly asymmetrical apparent affinities (low affinity inside). Therefore, net directional transport of large, neutral amino acids by system L depends on the parallel expression of a unidirectional transporter with overlapping selectivity (for instance systems A or N) that provides/recycles amino acids that drive system L exchange function. By mediating the regulated flux of these exchange substrates, unidirectional transporters control the activity of system L.

Amino acid transport Proximal kidney tubule Placenta Blood-brain barrier Membrane carrier 


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Copyright information

© Springer-Verlag 2003

Authors and Affiliations

  • François Verrey
    • 1
  1. 1.University of Zurich, Institute of Physiology, Winterthurerstrasse 190, 8057 Zürich, Switzerland

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