The binding specificity of amino acid transport system y+L in human erythrocytes is altered by monovalent cations

S. Angelo, C. Irarrázabal, R. Devés

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15 Scopus citations

Abstract

System y+L is a broad-scope amino acid transporter which binds and translocates cationic and neutral amino acids. Na+ replacement with K+ does not affect lysine transport, but markedly decreases the affinity of the transporter for L-leucine and L-glutamine. This observation suggests that the specificity of system y+L varies depending on the ionic composition of the medium. Here we have studied the interaction of the carrier with various amino acids in the presence of Na+, K+, Li+ and guanidinium ion. In agreement with the prediction, the specificity of system y+L was altered by the monovalent cations. In the presence of Na+, L-leucine was the neutral amino acid that interacted more powerfully. Elongation of the side chain (glycine - L-norleucine) strengthened binding. In contrast, bulkiness at the level of the β carbon was detrimental. In K+, the carrier behaved as a cationic amino acid specific carrier, interacting weakly with neutral amino acids. Li+ was found to potentiate neutral amino acid binding and in general the apparent affinities were higher than in Na+; elongation of the nonpolar side chain made a more important contribution to binding and the carrier was more tolerant towards β carbon substitution. Guanidinium stimulated the interaction of the carrier with neutral amino acids, but the effect was restricted to certain analogues (e.g., L-leucine, L-glutamine, L-methionine). Thus, in the presence of guanidinium, the carrier discriminates sharply among different neutral amino acids. The results suggest that the monovalent cations stabilize different carrier conformations.
Original languageAmerican English
Pages (from-to)37-44
Number of pages8
JournalJournal of Membrane Biology
Volume153
Issue number1
DOIs
StatePublished - 8 Oct 1996
Externally publishedYes

Keywords

  • Amino acids
  • Carrier
  • Lysine
  • Specificity
  • System y L +
  • Transport

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