Topographical similarities between harmaline inhibition sites on Na+-dependent amino acid transport system ASC in human erythrocytes and Na+-independent system asc in horse erythrocytes.
Abstract: Na+-dependent system ASC and Na+-independent system asc are characterized by a common selectivity for neutral amino acids of intermediate size such as L-alanine and by their interactions with dibasic amino acids. For system ASC, the positive charge on the dibasic amino acid side chain is considered to occupy the Na+-binding site on the transporter. We report here the use of harmaline (a Na+-site inhibitor in some systems) as a probe of possible structural homology between these two classes of amino acid transporter. Harmaline was found to inhibit human erythrocyte system ASC noncompetitively with respect to L-alanine concentration, but approximated competitive inhibition with respect to Na+ concentration (apparent Ki = 2.0 and 0.9 mM, respectively). Similarly, harmaline noncompetitively inhibited L-alanine uptake by horse erythrocyte systems asc1 and asc2 (apparent Ki = 2.0 and 1.9 mM, respectively). In contrast, harmaline functioned as a competitive inhibitor of L-lysine uptake by system asc1 (apparent Ki = 2.6 mM). It is concluded that harmaline competes with Na+ for binding to system ASC and that a topographically similar harmaline inhibition site is present on system asc. This site does not however bind Na+, the asc1 transporter exhibiting normal L-alanine and L-lysine influx kinetics in the total absence of extracellular cations.
Publication Date: 1988-01-05 PubMed ID: 3121605
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- Comparative Study
- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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The research explores the structural similarities between two types of amino acid transport systems in human and horse erythrocytes (red blood cells). The study uses harmaline, a known inhibitor of certain transport systems, to determine how it influences the transport of amino acids in these systems.
Study Objectives and Overview
- The primary intention of this study was to investigate potential structural homology (similarity in structure) between the sodium-dependent amino acid transport system ASC in human erythrocytes and the sodium-independent amino acid transport system asc in horse erythrocytes.
- The research used harmaline as a probe to explore this structural similarity. Harmaline inhibits certain transport systems by competing with sodium (Na+) for the Na+-binding site on the transporter.
Methodology and Findings
- The research found that harmaline inhibits both the human erythrocyte system ASC and the horse erythrocyte systems asc1 and asc2 non-competitively with respect to an amino acid L-alanine concentration.
- Notably, for the human system ASC, the harmaline inhibition approximated competitive inhibition with respect to the Na+ concentration.
- On the other hand, harmaline acted as a competitive inhibitor of L-lysine uptake by the horse system asc1, which indicates that harmaline competes with Na+ for binding to the asc1 system.
Conclusions
- The study concludes that a topographically comparable inhibition site exists between system ASC and system asc, as both exhibited similar properties with harmaline interference.
- This site, however, does not bind Na+ on the asc1 transporter, as shown by normal L-alanine and L-lysine influx kinetics, even in the absence of extracellular cations.
- These findings suggest that despite structural similarities, certain binding characteristics differ between these two classes of amino acid transporters.
Cite This Article
APA
Young JD, Mason DK, Fincham DA.
(1988).
Topographical similarities between harmaline inhibition sites on Na+-dependent amino acid transport system ASC in human erythrocytes and Na+-independent system asc in horse erythrocytes.
J Biol Chem, 263(1), 140-143.
Publication
Researcher Affiliations
- Department of Biochemistry, Faculty of Medicine, Chinese University of Hong Kong.
MeSH Terms
- Alanine / blood
- Alkaloids / pharmacology
- Amino Acids / blood
- Animals
- Biological Transport / drug effects
- Erythrocytes / drug effects
- Erythrocytes / metabolism
- Harmaline / pharmacology
- Horses
- Humans
- Kinetics
- Lysine / blood
- Sodium / pharmacology
- Species Specificity
Citations
This article has been cited 6 times.- Peter GJ, Davidson IG, Ahmed A, McIlroy L, Forrester AR, Taylor PM. Multiple components of arginine and phenylalanine transport induced in neutral and basic amino acid transporter-cRNA-injected Xenopus oocytes.. Biochem J 1996 Sep 15;318 ( Pt 3)(Pt 3):915-22.
- Devés R, Angelo S, Chávez P. N-ethylmaleimide discriminates between two lysine transport systems in human erythrocytes.. J Physiol 1993 Aug;468:753-66.
- Albi JL, Canals P, Gallardo MA, Sánchez J. Na(+)-independent L-alanine uptake by trout cells. Evidence for the existence of at least two functionally different acs systems.. J Membr Biol 1994 Jun;140(3):189-96.
- Gallardo MA, Ferrer MI, Sánchez J. Presence of X-AG carrier in frog (Rana esculenta) red blood cells.. J Membr Biol 1994 Apr;139(2):97-102.
- Williams TC, Doherty AJ, Griffith DA, Jarvis SM. Characterization of sodium-dependent and sodium-independent nucleoside transport systems in rabbit brush-border and basolateral plasma-membrane vesicles from the renal outer cortex.. Biochem J 1989 Nov 15;264(1):223-31.
- Su TZ, Logsdon CD, Oxender DL. Chinese hamster ovary mRNA-dependent, Na(+)-independent L-leucine transport in Xenopus laevis oocytes.. Mol Cell Biol 1992 Dec;12(12):5281-7.
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