scholarly journals Substrate specificity of amino acid transport in sheep erythrocytes

1977 ◽  
Vol 162 (1) ◽  
pp. 33-38 ◽  
Author(s):  
J D Young ◽  
J C Ellory
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Amino Acid Transport ◽  
Acid Transport ◽  
Inhibitory Potency ◽  
Amino Acid Transport System ◽  
Specific Amino Acid ◽  
Sheep Erythrocytes ◽  
Alpha Beta ◽  
Dibasic Amino Acids

The specificity of amino acid transport in normal (high-glutathione) sheep erythrocytes was investigated by studying the interaction of various neutral and dibasic amino acids in both competition and exchange experiments. Apparent Ki values were obtained for amino acids as inhibitors of L-alanine influx. Amino acids previously found to be transported by high-glutathione cells at fast rates (L-cysteine, L-alpha-amino-n-butyrate) were the most effective inhibitors. D-Alanine and D-alpha-amino-n-butyrate were without effect. Of the remaining amino acids studied, only L-norvaline, L-valine, L-norleucine, L-serine and L-2,4-diamino-n-butyrate significantly inhibited L-alanine uptake. L-Alanine efflux from pre-loaded cells was markedly stimulated by extracellular L-alanine. Those amino acids that inhibited L-alanine influx also stimulated L-alanine efflux. In addition, D-alanine, D-alpha-amino-n-biutyrate, L-threonine, L-asparagine, L-alpha, beta-diaminoproprionate, L-ornithine, L-lysine and S-2-aminoethyl-L-cysteine also significantly stimulated L-alanine efflux. L-Lysine uptake was inhibited by L-alanine but not by D-alanine, and the inhibitory potency of L-alanine was not influenced by the replacement of Na+ in the incubation medium with choline. L-Lysine efflux from pre-loaded cells was stimulated by L-alanine but not by D-alanine. It is concluded that these cells possess a highly selective stero-specific amino acid-transport system. Although the optimum substrates are small neutral amino acids, this system also has a significant affinity for dibasic amino acids.

Amino acid transport in human and in sheep erythrocytes

1980 ◽  
Vol 209 (1176) ◽  
pp. 355-375 ◽  
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Amino Acid Transport ◽  
Kinetic Studies ◽  
Transport Systems ◽  
Acid Transport ◽  
Sheep Erythrocytes ◽  
Neutral Amino Acids ◽  
L System ◽  
Dibasic Amino Acids

Amino acid transport was compared in human and in sheep erythrocytes. Kinetic studies established that human cells have three discrete amino acid transport systems, designated L, Ly + and ASC. The L system is partially stereospecific, with a preference for large neutral amino acids. L-leucine has a threefold lower apparent K m and a twofold smaller V max than D-leucine. Alanine, cysteine and possibly dibasic amino acids are transported by this route, but with a low affinity. The Ly + system is highly stereoselective, and specific for dibasic amino acids, including arginine. The ASC system is Na-dependent and selective for neutral amino acids of intermediate size. It has a particularly low apparent K m for cysteine and is stereospecific. Sheep erythrocytes lack these systems. Instead they possess an additional system (C system) responsible for the transport both of neutral and of dibasic amino acids, with cysteine as the optimal substrate. Although the substrate specificities of the human ASC and sheep C systems are similar, the sheep system does not require Na and has considerably higher apparent K m values. Dibasic amino acid transport (of lysine, but not of arginine) by the C system occurs with a low affinity.

scholarly journals Amino acid transport in normal and glutathione-deficient sheep erythrocytes

1976 ◽  
Vol 154 (1) ◽  
pp. 43-48 ◽  
Author(s):  
J D Young ◽  
J C Ellory ◽  
E M Tucker
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Amino Acid Transport ◽  
Cell Types ◽  
The Other ◽  
Acid Transport ◽  
Sheep Erythrocytes ◽  
Uptake Rates

1. Uptake rates for 23 amino acids were measured for both normal (high-GSH) and GSH-deficient (low-GSH) erythrocytes from Finnish Landrace sheep. 2. Compared with high-GSH cells, low-GSH cells had a markedly diminished permeability to D-alanine, L-alanine, α-amino-n-butyrate, valine, cysteine, serine, threonine, asparagine, lysine and ornithine. Smaller differences were observed for glycine and proline, whereas uptake of the other amino acids was not significantly different in the two cell types.

Cloning and functional characterization of a new subtype of the amino acid transport system N

2001 ◽  
Vol 281 (6) ◽  
pp. C1757-C1768 ◽  
Author(s):  
Takeo Nakanishi ◽  
Ramesh Kekuda ◽  
You-Jun Fei ◽  
Takahiro Hatanaka ◽  
Mitsuru Sugawara ◽  
...  
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Transport System ◽  
Amino Acid Transport ◽  
Mammalian Cells ◽  
Functional Characterization ◽  
Isobutyric Acid ◽  
Xenopus Laevis Oocytes ◽  
Acid Transport ◽  
Amino Acid Transport System

We have cloned a new subtype of the amino acid transport system N2 (SN2 or second subtype of system N) from rat brain. Rat SN2 consists of 471 amino acids and belongs to the recently identified glutamine transporter gene family that consists of system N and system A. Rat SN2 exhibits 63% identity with rat SN1. It also shows considerable sequence identity (50–56%) with the members of the amino acid transporter A subfamily. In the rat, SN2 mRNA is most abundant in the liver but is detectable in the brain, lung, stomach, kidney, testis, and spleen. When expressed in Xenopus laevis oocytes and in mammalian cells, rat SN2 mediates Na+-dependent transport of several neutral amino acids, including glycine, asparagine, alanine, serine, glutamine, and histidine. The transport process is electrogenic, Li+tolerant, and pH sensitive. The transport mechanism involves the influx of Na+ and amino acids coupled to the efflux of H+, resulting in intracellular alkalization. Proline, α-(methylamino)isobutyric acid, and anionic and cationic amino acids are not recognized by rat SN2.

scholarly journals Expression and adaptive regulation of amino acid transport system A in a placental cell line under amino acid restriction

Reproduction ◽  
2006 ◽  
Vol 131 (5) ◽  
pp. 951-960 ◽  
Author(s):  
H N Jones ◽  
C J Ashworth ◽  
K R Page ◽  
H J McArdle
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Cell Line ◽  
Transport System ◽  
Amino Acid Transport ◽  
Essential Amino Acids ◽  
Acid Transport ◽  
Amino Acid Transport System ◽  
Transcellular Transport ◽  
System A

Trans-placental transport of amino acids is vital for the developing fetus. Using the BeWo cell line as a placental model, we investigated the effect of restricting amino acid availability on amino acid transport system type A. BeWo cells were cultured either in amino acid-depleted (without non-essential amino acids) or control media for 1, 3, 5 or 6 h. System A function was analysed using α(methyl-amino)isobutyric acid (MeAIB) transcellular transport studies. Transporter (sodium coupled neutral amino acid transporter (SNAT1/2)) expression was analysed at mRNA and protein level by Northern and Western blotting respectively. Localisation was carried out using immunocytochemistry. MeAIB transcellular transport was significantly (P< 0.05) increased by incubation of the cells in amino acid-depleted medium for 1 h, and longer incubation times caused further increases in the rate of transfer. However, the initial response was not accompanied by an increase in SNAT2 mRNA; this occurred only after 3 h and further increased for the rest of the 6-h incubation. Similarly, it took several hours for a significant increase in SNAT2 protein expression. In contrast, relocalisation of existing SNAT2 transporters occurred within 30 min of amino acid restriction and continued throughout the 6-h incubation. When the cells were incubated in medium with even lower amino acid levels (without non-essential plus 0.5 × essential amino acids), SNAT2 mRNA levels showed further significant (P< 0.0001) up-regulation. However, incubation of cells in depleted medium for 6 h caused a significant (P= 0.014) decrease in the expression of SNAT1 mRNA. System L type amino acid transporter 2 (LAT2) expression was not changed by amino acid restriction, indicating that the responses seen in the system A transporters were not a general cell response. These data have shown that placental cells adaptin vitroto nutritional stress and have identified the physiological, biochemical and genomic mechanisms involved.

Intestinal Transport of Two Dipeptides Containing the Same Two Neutral Amino Acids in Man

1973 ◽  
Vol 45 (3) ◽  
pp. 291-299 ◽  
Author(s):  
D. B. A. Silk ◽  
D. Perrett ◽  
M. L. Clark
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Transport System ◽  
Amino Acid Transport ◽  
Amino Acid Mixture ◽  
Acid Mixture ◽  
Acid Transport ◽  
Peptide Hydrolysis ◽  
Amino Acid Transport System ◽  
Neutral Amino Acids

1. A double lumen perfusion technique has been used in man to study the absorption of the two neutral amino acids glycine and l-alanine from the two dipeptides, l-alanylglycine and glycyl-l-alanine and from an equivalent amino acid mixture. 2. Glycine was absorbed faster from the dipeptides than from the equivalent amino acid mixture, and the difference in absorption rates of glycine and alanine seen when the equimolar mixture of the amino acids was perfused, was abolished when either dipeptide was perfused. This suggests that dipeptides are taken up by the mucosal cell by a mechanism independent of the amino acid-transport system. 3. The presence of free amino acids in the lumen during perfusion of both dipeptides suggests that hydrolysis occurs at some stage in the uptake process. Intraluminal hydrolysis was insufficient to account for the concentration of the amino acids seen, and their presence is thought to be due to hydrolysis of the dipeptides at the brush border. 4. It is suggested that these results confirm that at least two modes of peptide absorption occur simultaneously, namely, direct peptide uptake, and peptide hydrolysis with subsequent absorption of the released amino acids by the amino acid transport system.

Characterization and regulation of the gene expression of amino acid transport system A (SNAT2) in rat mammary gland

2006 ◽  
Vol 291 (5) ◽  
pp. E1059-E1066 ◽  
Author(s):  
Adriana López ◽  
Nimbe Torres ◽  
Victor Ortiz ◽  
Gabriela Alemán ◽  
Rogelio Hernández-Pando ◽  
...  
Keyword(s):  
Gene Expression ◽  
Amino Acids ◽  
Mammary Gland ◽  
Amino Acid ◽  
Transport System ◽  
Amino Acid Transport ◽  
Acid Transport ◽  
Amino Acid Transport System ◽  
System A ◽  
Rat Mammary Gland

Amino acid transport via system A plays an important role during lactation, promoting the uptake of small neutral amino acids, mainly alanine and glutamine. However, the regulation of gene expression of system A [sodium-coupled neutral amino acid transporter (SNAT)2] in mammary gland has not been studied. The aim of the present work was to understand the possible mechanisms of regulation of SNAT2 in the rat mammary gland. Incubation of gland explants in amino acid-free medium induced the expression of SNAT2, and this response was repressed by the presence of small neutral amino acids or by actinomycin D but not by large neutral or cationic amino acids. The half-life of SNAT2 mRNA was 67 min, indicating a rapid turnover. In addition, SNAT2 expression in the mammary gland was induced by forskolin and PMA, inducers of PKA and PKC signaling pathways, respectively. Inhibitors of PKA and PKC pathways partially prevented the upregulation of SNAT2 mRNA during adaptive regulation. Interestingly, SNAT2 mRNA was induced during pregnancy and to a lesser extent at peak lactation. β-Estradiol stimulated the expression of SNAT2 in mammary gland explants; this stimulation was prevented by the estrogen receptor inhibitor ICI-182780. Our findings clearly demonstrated that the SNAT2 gene is regulated by multiple pathways, indicating that the expression of this amino acid transport system is tightly controlled due to its importance for the mammary gland during pregnancy and lactation to prepare the gland for the transport of amino acids during lactation.

Nonparticipation of extracellular glutathione in renal transport of dibasic amino acids

1979 ◽  
Vol 57 (10) ◽  
pp. 1168-1171 ◽  
Author(s):  
André G. Craan ◽  
Michel Bergeron
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Amino Acid Transport ◽  
Proximal Tubules ◽  
Methionine Sulfoximine ◽  
Acid Transport ◽  
Intracellular Glutathione ◽  
Direct Competition ◽  
Dibasic Amino Acid ◽  
Dibasic Amino Acids

Microinjections of L-[14C]arginine (2.9 mM) and L-[14C]ornithine (3.4 mM) were made into renal proximal tubules of rats in the presence of methionine sulfoximine (MSO) (10, 20 mM), ATP (10 mM), and MgCl2 (20 mM) together. Absorption of both labelled amino acids dropped, respectively, by 31.1 and 49.1% compared with control microinjections. The MSO alone or ATP plus MgCl2 had no effect. These data suggest that the inhibition by MSO plus ATP plus MgCl2 is not due to direct competition between MSO and dibasic amino acids but rather to suppression of the renewal of intracellular glutathione. Such an effect is discussed in comparison with cycloleucine inhibition of dibasic amino acid transport. Addition of exogenous glutathione to microinjectates did not reverse either type of inhibition. This study shows that while intracellular glutathione may affect amino acid transport, extracellular glutathione has no effect.

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