scholarly journals Transport of Methylmercury through the Epithelial Type Amino Acid Transporter System B0

2019 ◽  
Vol 5 (2) ◽  
pp. 127-136
Author(s):  
Rafiqul Islam ◽  
Naohiko Anzai ◽  
Nesar Ahmed ◽  
Mohammad Ahtashamul Haque ◽  
Shamima Ferdous ◽  
...  
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Molecular Mechanism ◽  
Xenopus Oocytes ◽  
Critical Role ◽  
Amino Acid Transporter ◽  
Intestinal Lumen ◽  
Dependent Manner ◽  
Sodium Dependent ◽  
Acid Transporter

Background: System B0 is a sodium dependent transporter that transports wide variety of neutral amino acids in the intestinal and renal proximal tubular epithelial cells. Methylmercury (MeHg) readily and non-enzymatically reacts with cysteine to form conjugate structurally similar to the amino acid methionine. Objective: In this study, we investigated the molecular mechanism of absorptive transport of MeHg in intestine using Xenopus oocytes expressing hB0AT1 and the uptake of metylmercry-Cys (MeHg-Cys) by heterodimeric amino acids transporter. Methodology: We confirmed the uptake of [14C] L-Leucine a potent substrate for the hB0AT1 amino acids transporter. The uptake of [14C] L-leucine by hB0AT1 was inhibited by MeHg-Cys conjugate, leucine, cysteine, methinine and phenylalanine in concentration–dependent manner. The IC50 of MeHg-Cys conjugate was significantly lower than that of leucine, cysteine, methinine and phenylalanine, indicating that hB0AT1 is a high affinity MeHg transporter. To assess MeHg-Cys conjugate transport, we measured [14C] MeHg uptake in Xenopus oocytes expressing hB0AT1 in presence or absence of sodium. The [14C] MeHg was transport only in the presence of cysteine and the transport was significantly sodium dependent and inhibited by a system B0 inhibitor 2-aminobicyclo-[2,21]- haptane-2-carboxylic acid (BCH). Result: The current findings indicate that hB0AT1 and heterodimeric amino acids absorb MeHg in the form of cysteine conjugate from the intestinal lumen across the brush-border membrane in to the cells and is supposed to be plays a critical role in the pathogenesis of Minamata disease and present results descried a major molecular mechanism by which MeHg is transported across cell membranes and indicate that metal complexes may form a novel class of substrates for amino acid carriers. Conclusion: In this experiment the results also suggest that uptake of Methionine and MeHg-Cys by heterodimeric amino acid transporter is significantly correlated where the uptake of Methionine and MeHg-Cys between heterodimeric amino acid transporter and hB0AT1 is not correlated. Journal of National Institute of Neurosciences Bangladesh, 2019;5(2): 127-136

scholarly journals Neutral amino acid transporter ASCT2 displays substrate-induced Na+ exchange and a substrate-gated anion conductance

2000 ◽  
Vol 346 (3) ◽  
pp. 705-710 ◽  
Author(s):  
Angelika BRÖER ◽  
Carsten WAGNER ◽  
Florian LANG ◽  
Stefan BRÖER
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Anion Channel ◽  
Amino Acid Transporter ◽  
Neutral Amino Acid ◽  
Xenopus Laevis Oocytes ◽  
Anion Conductance ◽  
Neutral Amino Acid Transporter ◽  
Inward Currents ◽  
Acid Transporter

The neutral amino acid transporter ASCT2 mediates electroneutral obligatory antiport but at the same time requires Na+ for its function. To elucidate the mechanism, ASCT2 was expressed in Xenopus laevis oocytes and transport was analysed by flux studies and two-electrode voltage clamp recordings. Flux studies with 22NaCl indicated that the uptake of one molecule of glutamine or alanine is accompanied by the uptake of four to seven Na+ ions. Similarly to the transport of amino acids, the Na+ uptake was mediated by an obligatory Na+ exchange mechanism that depended on the presence of amino acids but was not stoichiometrically coupled to the amino acid transport. Other cations could not replace Na+ in this transport mechanism. When NaCl was replaced by NaSCN in the transport buffer, the superfusion of oocytes with amino acid substrates resulted in large inward currents, indicating the presence of a substrate-gated anion channel in the ASCT2 transporter. The Km for glutamine derived from these experiments is in good agreement with the Km derived from flux studies; it varied between 40 and 90 μM at holding potentials of -60 and -20 mV respectively. The permeability of the substrate-gated anion conductance decreased in the order SCN- NO3- > I- > Cl- and also required the presence of Na+.

Estradiol inhibits the activity of proton-coupled amino acid transporter PAT1 expressed in Xenopus oocytes

2012 ◽  
Vol 695 (1-3) ◽  
pp. 34-39
Author(s):  
Linlin Shan ◽  
Yujie Yang ◽  
Jin Wang ◽  
Ji Zuo ◽  
Xianhong Dong ◽  
...  
Keyword(s):  
Amino Acid ◽  
Xenopus Oocytes ◽  
Amino Acid Transporter ◽  
Acid Transporter

scholarly journals Multiple components of arginine and phenylalanine transport induced in neutral and basic amino acid transporter-cRNA-injected Xenopus oocytes

1996 ◽  
Vol 318 (3) ◽  
pp. 915-922 ◽  
Author(s):  
George J PETER ◽  
Iain G. DAVIDSON ◽  
Aamir AHMED ◽  
Lynn McILROY ◽  
Alexander R. FORRESTER ◽  
...  
Keyword(s):  
Amino Acid ◽  
Xenopus Oocytes ◽  
Competitive Inhibition ◽  
Protein Complexes ◽  
Basic Amino Acid ◽  
Amino Acid Transporter ◽  
Transport Processes ◽  
Arginine Transport ◽  
Acid Transporter ◽  
Phenylalanine Transport

The induced uptakes of l-[3H]phenylalanine and l-[3H]arginine in oocytes injected with clonal NBAT (neutral and basic amino acid transporter) cRNA show differential inactivation by pre-treatment with N-ethylmaleimide (NEM), revealing at least two distinct transport processes. NEM-resistant arginine transport is inhibited by leucine and phenylalanine but not by alanine or valine; mutual competitive inhibition of NEM-resistant uptake of arginine and phenylalanine indicates that the two amino acids share a single transporter. NEM-senstive arginine transport is inhibited by leucine, phenylalanine, alanine and valine. At least two NEM-sensitive transporters may be expressed because we have been unable to confirm mutual competitive inhibition between arginine and phenylalanine transport. The NEM-resistant transport mechanism appears to involve distinct but overlapping binding sites for cationic and zwitterionic substrates. NBAT is known to form oligomeric protein complexes in cell membranes, and its functional roles when expressed in Xenopus oocytes may include interaction with oocyte proteins, leading to increased native amino acid transport activities; these resemble NBAT-expressed activities in terms of NEM-sensitivity and apparent substrate range (including an unusual inhibition by β-phenylalanine).

scholarly journals Intestinal peptidases form functional complexes with the neutral amino acid transporter B0AT1

2012 ◽  
Vol 446 (1) ◽  
pp. 135-148 ◽  
Author(s):  
Stephen J. Fairweather ◽  
Angelika Bröer ◽  
Megan L. O'Mara ◽  
Stefan Bröer
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Amino Acid Transporter ◽  
The Body ◽  
Site Directed Mutagenesis ◽  
Substrate Affinity ◽  
Xenopus Laevis Oocytes ◽  
Acid Transporter

The brush-border membrane of the small intestine and kidney proximal tubule are the major sites for the absorption and re-absorption of nutrients in the body respectively. Transport of amino acids is mediated through the action of numerous secondary active transporters. In the mouse, neutral amino acids are transported by B0AT1 [broad neutral (0) amino acid transporter 1; SLC6A19 (solute carrier family 6 member 19)] in the intestine and by B0AT1 and B0AT3 (SLC6A18) in the kidney. Immunoprecipitation and Blue native electrophoresis of intestinal brush-border membrane proteins revealed that B0AT1 forms complexes with two peptidases, APN (aminopeptidase N/CD13) and ACE2 (angiotensin-converting enzyme 2). Physiological characterization of B0AT1 expressed together with these peptidases in Xenopus laevis oocytes revealed that APN increased the substrate affinity of the transporter up to 2.5-fold and also increased its surface expression (Vmax). Peptide competition experiments, in silico modelling and site-directed mutagenesis of APN suggest that the catalytic site of the peptidase is involved in the observed changes of B0AT1 apparent substrate affinity, possibly by increasing the local substrate concentration. These results provide evidence for the existence of B0AT1-containing digestive complexes in the brush-border membrane, interacting differentially with various peptidases, and responding to the dynamic needs of nutrient absorption in the intestine and kidney.

scholarly journals Size does matter: 18 amino acids at the N-terminal tip of an amino acid transporter in Leishmania determine substrate specificity

2015 ◽  
Vol 5 (1) ◽  
Author(s):  
Doreen Schlisselberg ◽  
Eldar Mazarib ◽  
Ehud Inbar ◽  
Doris Rentsch ◽  
Peter J. Myler ◽  
...  
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Substrate Specificity ◽  
Amino Acid Transporter ◽  
Acid Transporter
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