Mammalian Amino Acid Transport System y+ Revisited: Specificity and Cation Dependence of the Interaction with Neutral Amino Acids

Mammalian Amino Acid Transport System y+ Revisited: Specificity and Cation Dependence of the... A reevaluation of the specificity of system y+, the classical transporter for cationic amino acids is presented. System y+ has been defined as a transporter for cationic amino acids that binds neutral amino acids with lower affinity in the presence of Na+. The discovery of other transporters for cationic amino has suggested that some properties, originally attributed to system y+, may relate to other transport systems. Uncertainty concerns mainly, the affinity for neutral amino acids and the cation dependence of this interaction. Neutral amino acids (13 analogues tested) were found to bind to system y+ in human erythrocytes with very low affinity. Inhibition constants (Kiy, mm) ranged between 14.2 mm and >400 mm, and the strength of interaction was similar in the presence of Na+, K+ or Li+ (145 mm). In choline medium, no interaction was detected up to 20 mm of the neutral amino acid. Guanidinium ion (5 mm, osmolarity maintained with choline) potentiated neutral amino acid binding; the effect was most important in the case of l-norvaline which aligned with guanidinium ion is equivalent to arginine. This suggests cooperative interaction at the substrate site. The specificity of system y+ was shown to be clearly distinct from that of system y+L, a cationic amino acid transporter that accepts neutral amino acids with high affinity in the presence of Na+ and which influenced the classical definition of system y+. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Membrane Biology Springer Journals

Mammalian Amino Acid Transport System y+ Revisited: Specificity and Cation Dependence of the Interaction with Neutral Amino Acids

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Publisher
Springer-Verlag
Copyright
Copyright © Inc. by 1999 Springer-Verlag New York
Subject
Life Sciences; Biochemistry, general; Human Physiology
ISSN
0022-2631
eISSN
1432-1424
D.O.I.
10.1007/s002329900509
Publisher site
See Article on Publisher Site

Abstract

A reevaluation of the specificity of system y+, the classical transporter for cationic amino acids is presented. System y+ has been defined as a transporter for cationic amino acids that binds neutral amino acids with lower affinity in the presence of Na+. The discovery of other transporters for cationic amino has suggested that some properties, originally attributed to system y+, may relate to other transport systems. Uncertainty concerns mainly, the affinity for neutral amino acids and the cation dependence of this interaction. Neutral amino acids (13 analogues tested) were found to bind to system y+ in human erythrocytes with very low affinity. Inhibition constants (Kiy, mm) ranged between 14.2 mm and >400 mm, and the strength of interaction was similar in the presence of Na+, K+ or Li+ (145 mm). In choline medium, no interaction was detected up to 20 mm of the neutral amino acid. Guanidinium ion (5 mm, osmolarity maintained with choline) potentiated neutral amino acid binding; the effect was most important in the case of l-norvaline which aligned with guanidinium ion is equivalent to arginine. This suggests cooperative interaction at the substrate site. The specificity of system y+ was shown to be clearly distinct from that of system y+L, a cationic amino acid transporter that accepts neutral amino acids with high affinity in the presence of Na+ and which influenced the classical definition of system y+.

Journal

The Journal of Membrane BiologySpringer Journals

Published: Mar 15, 1999

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