SMIT2 mediates all myo-inositol uptake in apical membranes of rat small intestine

2007 ◽  
Vol 293 (6) ◽  
pp. G1300-G1307 ◽  
Author(s):  
Rym Aouameur ◽  
Sandra Da Cal ◽  
Pierre Bissonnette ◽  
Michael J. Coady ◽  
Jean-Yves Lapointe
Keyword(s):  
Small Intestine ◽  
Transport System ◽  
Sugar Transport ◽  
Transport Systems ◽  
Affinity Constant ◽  
Rat Intestine ◽  
Electrophysiological Studies ◽  
Rabbit Intestine ◽  
Apical Membranes ◽  
Inhibition Studies

This study presents the characterization of myo-inositol (MI) uptake in rat intestine as evaluated by use of purified membrane preparations. Three secondary active MI cotransporters have been identified; two are Na+ coupled (SMIT1 and SMIT2) and one is H+ coupled (HMIT). Through inhibition studies using selective substrates such as d-chiro-inositol (DCI, specific for SMIT2) and l-fucose (specific for SMIT1), we show that SMIT2 is exclusively responsible for apical MI transport in rat intestine; rabbit intestine appears to lack apical transport of MI. Other sugar transport systems known to be present in apical membranes, such as SGLT1 or GLUT5, lacked any significant contribution to MI uptake. Functional analysis of rat SMIT2 activity, via electrophysiological studies in Xenopus oocytes, demonstrated similarities to the activities of SMIT2 from other species (rabbit and human) displaying high affinities for MI (0.150 ± 0.040 mM), DCI (0.31 ± 0.06 mM), and phlorizin (Pz; 0.016 ± 0.007 mM); low affinity for glucose (36 ± 7 mM); and no affinity for l-fucose. Although these functional characteristics essentially confirmed those found in rat intestinal apical membranes, a unique discrepancy was seen between the two systems studied in that the affinity constant for glucose was ∼40-fold lower in vesicles ( Ki = 0.94 ± 0.35 mM) than in oocytes. Finally, the transport system responsible for the basolateral efflux transporter of glucose in intestine, GLUT2, did not mediate any significant radiolabeled MI uptake in oocytes, indicating that this transport system does not participate in the basolateral exit of MI from small intestine.

scholarly journals The Glucuronic Acid Utilization Gene Cluster from Bacillus stearothermophilus T-6

1999 ◽  
Vol 181 (12) ◽  
pp. 3695-3704 ◽  
Author(s):  
Smadar Shulami ◽  
Orit Gat ◽  
Abraham L. Sonenshein ◽  
Yuval Shoham
Keyword(s):  
Gene Cluster ◽  
Transport System ◽  
Bacillus Stearothermophilus ◽  
Glucuronic Acid ◽  
Genomic Library ◽  
Regulatory Gene ◽  
Sugar Transport ◽  
Transcriptional Unit ◽  
Transport Systems ◽  
Potential Operator

ABSTRACT A λ-EMBL3 genomic library of Bacillus stearothermophilus T-6 was screened for hemicellulolytic activities, and five independent clones exhibiting β-xylosidase activity were isolated. The clones overlap each other and together represent a 23.5-kb chromosomal segment. The segment contains a cluster of xylan utilization genes, which are organized in at least three transcriptional units. These include the gene for the extracellular xylanase, xylanase T-6; part of an operon coding for an intracellular xylanase and a β-xylosidase; and a putative 15.5-kb-long transcriptional unit, consisting of 12 genes involved in the utilization of α-d-glucuronic acid (GlcUA). The first four genes in the potential GlcUA operon (orf1, -2, -3, and -4) code for a putative sugar transport system with characteristic components of the binding-protein-dependent transport systems. The most likely natural substrate for this transport system is aldotetraouronic acid [2-O-α-(4-O-methyl-α-d-glucuronosyl)-xylotriose] (MeGlcUAXyl3). The following two genes code for an intracellular α-glucuronidase (aguA) and a β-xylosidase (xynB). Five more genes (kdgK,kdgA, uxaC, uxuA, anduxuB) encode proteins that are homologous to enzymes involved in galacturonate and glucuronate catabolism. The gene cluster also includes a potential regulatory gene, uxuR, the product of which resembles repressors of the GntR family. The apparent transcriptional start point of the cluster was determined by primer extension analysis and is located 349 bp from the initial ATG codon. The potential operator site is a perfect 12-bp inverted repeat located downstream from the promoter between nucleotides +170 and +181. Gel retardation assays indicated that UxuR binds specifically to this sequence and that this binding is efficiently prevented in vitro by MeGlcUAXyl3, the most likely molecular inducer.

Specificity of sugar transport by the intestine of the hamster

1960 ◽  
Vol 198 (1) ◽  
pp. 99-102 ◽  
Author(s):  
T. Hastings Wilson ◽  
Bernard R. Landau
Keyword(s):  
Small Intestine ◽  
Transport System ◽  
Concentration Gradient ◽  
Sugar Transport ◽  
Intestinal Wall ◽  
Sugar Derivatives

The specificity of the sugar transport system of the hamster small intestine was tested with 20 sugars and sugar derivatives not previously tested in this system. The absorption of sugars across the intestinal wall against a concentration gradient was tested with the everted sac technique in vitro. 3-Deoxyglucose, 4-0-methylgalactose, 6-deoxy-6-fluoroglucose and α-methylglucoside were transported while a variety of other sugars were not. From the data derived from the study of a total of 49 sugars tested in this system, certain generalizations are made as to the structural limitations of the sugar-absorbing capacity of the hamster intestine.

scholarly journals 2-Deoxy-d-galactose, a substrate for the galactose-transport system of Escherichia coli

1977 ◽  
Vol 168 (1) ◽  
pp. 15-22 ◽  
Author(s):  
P J F Henderson ◽  
R A Giddens
Keyword(s):  
Escherichia Coli ◽  
Transport System ◽  
Transport Systems ◽  
Mutual Inhibition ◽  
E Coli ◽  
System 2 ◽  
Galactose Transport ◽  
Proton Uptake ◽  
Inhibition Studies ◽  
Lactose Transport

The following observations showed that 2-deoxy-D-galactose is a useful tool for the isolation and elucidation of the activity of one system for galactose uptake into Escherichia coli. 1. 2-Deoxygalactose, which is not a substrate for growth of E. coli, was transported into strains of the organism induced for galactose transport. 2. By using appropriate mutants it was shown that 2-deoxygalactose is a much better substrate for the galactose-transport system than for the methyl galactoside-transport system. This was confirmed by the results of mutual inhibition studies with substrates of each transport system. 3. The glucose-, arabinose- or lactose-transport systems did not effect significant transport of 2-deoxygalactose. 4. Like other substrates of the galactose-transport system, 2-deoxygalactose promoted effective proton uptake into de-energized suspensions of appropriate E. coli strains. 5. The S183 series of E. coli mutants were found to contain a constitutive galactose-transport system, if 2-deoxygalactose transport is used as one criterion for such activity.

Effects of phloretin and theophylline on 3-O-methylglucose transport by intestinal epithelial cells

1978 ◽  
Vol 234 (3) ◽  
pp. C64-C72 ◽  
Author(s):  
J. Randles ◽  
G. A. Kimmich
Keyword(s):  
Epithelial Cells ◽  
Transport System ◽  
Intestinal Epithelial Cells ◽  
Sugar Transport ◽  
Inhibitory Effect ◽  
Metabolic Effects ◽  
Transport Systems ◽  
Facilitated Diffusion ◽  
Intestinal Epithelial ◽  
Gradient Enhancement

Phloretin and theophylline each exert an immediate inhibitory effect on the Na+-independent, facilitated-diffusion transport system for sugar associated with intestinal epithelial cells. Phloretin inhibits approximately 50% more of the total Na+-independent sugar flux than theophylline. Neither agent has an immediate effect on the Na+-dependent, concentrative sugar transport system, although preincubation of the cells with phloretin causes a significant inhibition. The slowly developing effect is correlated with a decrease in cellular adenosine triphosphate (ATP) and an elevation of intracellular Na+. Other agents which elevate cell Na+ also inhibit Na+-dependent sugar influx, even if ATP levels are not depleted. On the other hand, if ATP is depleted by phloretin under conditions in which the cells do not gain Na+, the inhibitory effect on Na+-dependent sugar flux tends to disappear. The slow-onset phloretin effects are due to transinhibition of the Na+-dependent sugar carrier by cellular Na+. When the passive sugar carrier is inhibited by phloretin or theophylline, the concentrative system can establish an enhanced sugar gradient. Because of the secondary metabolic effects of phloretin, theophylline induces a greater gradient enhancement despite its more limited effect on the passive sugar-transport system. Sugar gradients as large as 20-fold are induced by theophylline, in contrast to 12-fold gradients observed in the presence of phloretin and approximately 7- to 8-fold for untreated cells. These results are discussed in terms of conceptual questions regarding the energetics of Na+-dependent transport systems.

Functional involvement of RFVT3/SLC52A3 in intestinal riboflavin absorption

2014 ◽  
Vol 306 (2) ◽  
pp. G102-G110 ◽  
Author(s):  
Hiroki Yoshimatsu ◽  
Atsushi Yonezawa ◽  
Yoshiaki Yao ◽  
Kumiko Sugano ◽  
Shunsaku Nakagawa ◽  
...  
Keyword(s):  
Methylene Blue ◽  
Small Intestine ◽  
Epithelial Cells ◽  
Intestinal Epithelial Cells ◽  
Biological Membrane ◽  
Transport Systems ◽  
Intestinal Epithelial ◽  
T84 Cells ◽  
Functional Involvement ◽  
Apical Membranes

Riboflavin, also known as vitamin B2, is transported across the biological membrane into various organs by transport systems. Riboflavin transporter RFVT3 is expressed in the small intestine and has been suggested to localize in the apical membranes of the intestinal epithelial cells. In this study, we investigated the functional involvement of RFVT3 in riboflavin absorption using intestinal epithelial T84 cells and mouse small intestine. T84 cells expressed RFVT3 and conserved unidirectional riboflavin transport corresponding to intestinal absorption. Apical [3H]riboflavin uptake was pH-dependent in T84 cells. This uptake was not affected by Na+ depletion at apical pH 6.0, although it was significantly decreased at apical pH 7.4. The [3H]riboflavin uptake from the apical side of T84 cells was prominently inhibited by the RFVT3 selective inhibitor methylene blue and significantly decreased by transfection of RFVT3-small-interfering RNA. In the gastrointestinal tract, RFVT3 was expressed in the jejunum and ileum. Mouse jejunal and ileal permeabilities of [3H]riboflavin were measured by the in situ closed-loop method and were significantly reduced by methylene blue. These results strongly suggest that RFVT3 would functionally be involved in riboflavin absorption in the apical membranes of intestinal epithelial cells.

Specificity of the imino acid carrier in rat small intestine

1994 ◽  
Vol 266 (4) ◽  
pp. R1154-R1161 ◽  
Author(s):  
B. G. Munck ◽  
L. K. Munck ◽  
S. N. Rasmussen ◽  
A. Polache
Keyword(s):  
Small Intestine ◽  
Guinea Pig ◽  
Rat Small Intestine ◽  
Gamma Aminobutyric Acid ◽  
Monocarboxylic Acids ◽  
Beta Alanine ◽  
Imino Acid ◽  
Maximal Activation ◽  
Rabbit Intestine ◽  
Inhibition Studies

The rat intestinal imino acid carrier is chloride independent, while in guinea pig and rabbit intestine it is chloride dependent. While non-alpha-amino acids do not significantly interact with guinea pig and rabbit imino acid carriers, inhibition studies had indicated that in rat small intestine beta-alanine, gamma-aminobutyric acid (GABA), and probably taurine might be transported by the imino acid carrier. The present study of rat jejunum demonstrates that the half-maximal activation concentration of beta-alanine (K1/2 beta-Ala) is identical to its inhibition constant (Ki beta-Ala) against GABA, that K1/2GABA is identical to KiGABA against beta-alanine, that proline and sarcosine have identical values of Ki against beta-alanine and GABA, and that Ki of beta-alanine and proline against sarcosine are equal to their K1/2 values. Taurine inhibits the transport of beta-alanine, and 300 mM proline and beta-alanine reduce the transport of taurine measured at 80 mM taurine to the level expected for the diffusive contribution, corresponding to Ki values equal to those against sarcosine. Thus the rat imino acid carrier is the principal carrier of taurine and the only carrier of beta-alanine and GABA. It is also demonstrated that alpha-amino-monocarboxylic acids with side chains in excess of one methyl group do not significantly interact with the imino acid carrier, and the lack of stereospecificity is confirmed.

scholarly journals An explanation of the asymmetric binding of sugars to the human erythrocyte sugar-transport systems

1973 ◽  
Vol 135 (3) ◽  
pp. 539-541 ◽  
Author(s):  
J. E. G. Barnett ◽  
G. D. Holman ◽  
K. A. Munday
Keyword(s):  
Transport System ◽  
Human Erythrocyte ◽  
Sugar Transport ◽  
Transport Systems

6-O-Alkyl-d-galactoses competitively inhibit the erythrocyte sugar-transport system when added to the outside of the cells, but not to the inside. n-Propyl β-d-glucopyranoside competitively inhibits the system on the inside of the cells, but not on the outside. A model for sugar transport is proposed.

Renal sugar transport in the winter flounder. III. Two glucose transport systems

1977 ◽  
Vol 232 (3) ◽  
pp. F227-F234 ◽  
Author(s):  
A. Kleinzeller ◽  
G. R. Dubyak ◽  
P. M. Griffin ◽  
E. M. McAvoy ◽  
J. M. Mullin ◽  
...  
Keyword(s):  
Hydrogen Bonding ◽  
Glucose Transport ◽  
Transport System ◽  
Sugar Transport ◽  
Winter Flounder ◽  
Transport Systems ◽  
Renal Tubules ◽  
Pyranose Ring ◽  
Structural Requirements ◽  
Specificity Pattern

Teased renal tubules of the winter flounder (Pseudopleuronectes americanus) were employed to investigate the structural requirements for two pathways of D-glucose transport which take place preponderantly across the basal (antiluminal) face of renal cells. 1) An inhibition analysis of the equilibrating, Na-independent and phlorizin-sensitive transport of the nonmetabolizable methyl-alpha-D-glucoside (0.1 and 0.5 mM), with 20 glucose analogs (5 mM), was employed to establish the structural requirements for the substrate-carrier interaction: a (pyranose) ring, oxygen, or F at C1, C2-OH, C3-OH, and C4-OH (all axial, 1C model). Some interaction may also occur at C6-OH. D-Glucose shares this transport system. Hydrogen bonding between the oxygens and the carrier is suggested. 2) The phloretin- and phlorizin-sensitive, ouabain-insensitive transport of D-glucose, 2-deoxy-D-glucose, and D-mannose is associated with considerable phosphorylation. The three sugars mutually compete for a shared transport site. The specificity pattern characterizing the transport system defines the following structural requirements: a (pyranose) ring, a free C1-OH, C3-OH, and C4-OH (both axial) and possibly C6-OH. Hydrogen bonding between the carrier and the oxygens at C3, C4, and C6, and covalent bonding at C1 is suggested.

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