Fructose transport byHaloferax volcanii

1995 ◽  
Vol 41 (3) ◽  
pp. 241-246 ◽  
Author(s):  
Jin-Ichiro Takano ◽  
Kouichi Kaidoh ◽  
Naoki Kamo
Keyword(s):  
Kinetic Analysis ◽  
Glucose Uptake ◽  
Glucose Transport ◽  
Transport System ◽  
Driving Force ◽  
Glucose Transporter ◽  
Potential Gradient ◽  
Haloferax Volcanii ◽  
Intact Cells ◽  
Glucose Transport System

Uptake of fructose by intact cells of Haloferax volcanii, one of the sugar-utilizing halobacteria, was examined with the following results. (i) The fructose transporter was inducible, (ii) Kinetic analysis showed a Ktof 0.37 μM and a Vmaxof 4.61 nmol∙mg protein−1∙min−1. For a glucose transport system in this bacterium, Ktwas 12.5 μM, showing that the fructose transporter had a much larger affinity for a substrate than the glucose transporter, (iii) No uptake was observed by the envelope vesicles, (iv) Phloridzin and phloretin inhibited fructose transport, although a relatively higher concentration was required than that needed to inhibit glucose uptake, (v) The driving force for fructose transport was a Na+electrochemical potential gradient, (vi) Glucose and fructose were interchangeable and this conversion led to the expression of the glucose transporter even when fructose was used as the sole carbohydrate, and vice versa.Key words: glucose uptake, symport with Na+, phloridzin, phloretin, Haloferax volcanii.

Hyperpolarization as a mediator of insulin action: increased muscle glucose uptake induced electrically

1980 ◽  
Vol 239 (1) ◽  
pp. E21-E29 ◽  
Author(s):  
K. Zierler ◽  
E. M. Rogus
Keyword(s):  
Glucose Uptake ◽  
Glucose Transport ◽  
Transport System ◽  
Continuous Flow ◽  
Insulin Action ◽  
Interstitial Fluid ◽  
The Other ◽  
Glucose Transport System ◽  
Sucrose Gap ◽  
Whole Muscle

Insulin hyperpolarizes. This raises the questions: is hyperpolarization a means by which insulin exerts some of its other effects, and can electrically induced hyperpolarization mimic insulin action on membrane functions? A technique was devised to study the latter question. The technique permits electrical hyperpolarization of a segment of whole muscle. Rat caudofemoralis muscle was threaded into a triple sucrose-gap chamber. Continuous flow of sucrose displaced interstitial fluid of muscle segments in the gaps. In one electrolyte compartment between gaps was placed an anode and in the other a cathode. The muscle segment in the anodal compartment was hyperpolarized continuously for 30 min, probably by about 1.5 mV. Uptake of deoxyglucose was increased in the hyperpolarized muscle segment. This increase, by 39%, was highly significant. It was probably smaller than the twofold increase elicited by insulin (100 mU/ml), but not than the possible effect produced by 10 mU/ml. The effect of hyperpolarization was specific for the D-glucose transport system because uptake of L-glucose was not altered.

scholarly journals Dapagliflozin: A Once-Daily Oral Therapy Sodium-Glucose Cotransporter-2 Inhibitor for the Treatment of Adult Patients with Type 2 Diabetes

2011 ◽  
Vol 3 ◽  
pp. CMT.S6168 ◽  
Author(s):  
Khalid Jadoon ◽  
Iskandar Idris
Keyword(s):  
Adverse Effects ◽  
Glucose Transport ◽  
Transport System ◽  
Glucose Transporter ◽  
Intestinal Transport ◽  
Selective Inhibition ◽  
Genetic Syndromes ◽  
Glucose Levels ◽  
Glucose Transporter 2 ◽  
Glucose Transport System

The induction of glycosuria using phlorizin, a nonselective inhibitor of renal and intestinal transport was well recognised to lower glucose levels and induce calorie loss in animal models of diabetes. Phlorizin and other similar molecules however were not suitable for clinical use due to adverse effects of non selective inhibition of extra-renal glucose transport system. More recent understanding of the physiology of renal glucose transport system and increased knowledge of rare genetic syndromes of renal glycosuria has resulted in the development of drugs that selectively inhibit the Sodium Glucose Transporter-2 (SGLT2). Among the various agents currently being developed within this drug class, dapagliflozin is the most advanced in clinical development. This article discusses the basic physiology of the SGLT2 transporter system, pharmacokinetics and pharmacodynamic information of dapagliflozin, its efficacy in lowering HbA1c and weight as well as its safety and adverse effects profile. This is discussed based on evidence derived from clinical trials involving a spectrum of patients with diabetes, from drug naïve to individuals already on insulin therapy.

Rate-limiting steps for insulin-mediated glucose uptake into perfused rat hindlimb

1986 ◽  
Vol 250 (1) ◽  
pp. E100-E102 ◽  
Author(s):  
K. Kubo ◽  
J. E. Foley
Keyword(s):  
Glucose Uptake ◽  
Glucose Transport ◽  
Transport System ◽  
Glucose Concentration ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Glucose Transport System ◽  
Glucose Clearance ◽  
Rate Limiting ◽  
Uptake And Metabolism

To determine the glucose and insulin concentrations at which glucose transport is rate limiting for insulin-mediated glucose uptake and metabolism in muscle, glucose clearance was determined in the presence of glucose concentrations ranging from trace to 20 mM and in the absence or presence of insulin in the perfused rat hindlimb. In the absence of insulin and at submaximally stimulating insulin concentrations glucose clearance was constant up to 7 mM glucose and then decreased as the glucose concentration was raised. At maximally stimulating insulin concentrations glucose clearance was constant up to 2 mM glucose and then decreased. The decrease in glucose clearance between 2 and 7 mM glucose in the presence of maximally stimulating insulin concentrations could not be accounted for by competition among glucose molecules for the glucose transport system. The results suggest that at physiological glucose concentrations in the presence of maximally stimulating insulin concentrations the rate-limiting step for insulin-mediated glucose uptake and metabolism in muscle shifts from glucose transport to some step beyond transport.

Exercise training and the glucose transport system in obese SHHF/Mcc-fa cprats

1996 ◽  
Vol 81 (4) ◽  
pp. 1670-1676 ◽  
Author(s):  
Cynthia M. Ferrara ◽  
W. Michael Sherman ◽  
Nicole Leenders ◽  
Sylvia A. McCune ◽  
Karla Roehrig
Keyword(s):  
Plasma Membrane ◽  
Exercise Training ◽  
Glucose Transport ◽  
Transport System ◽  
Glucose Transporter ◽  
Citrate Synthase ◽  
Training Stimulus ◽  
Peak Oxygen Uptake ◽  
Glucose Transport System ◽  
Obese Male

Ferrara, Cynthia M., W. Michael Sherman, Nicole Leenders, Sylvia A. McCune, and Karla Roehrig. Exercise training and the glucose transport system in obese SHHF/ Mcc-fa cprats. J. Appl. Physiol. 81(4): 1670–1676, 1996.—The effects of a similar exercise training stimulus on maximal insulin-stimulated (MIS) plasma membrane glucose transporter number and glucose transport were determined in lean and obese SHHF/ Mcc-fa cprats. Six-week-old lean and obese male rats were randomly divided into four groups: lean sedentary (LSed), obese sedentary (OSed), lean exercise (LEx), and obese exercise (OEx). An 8- to 12-wk treadmill running program equalized daily muscular work for LEx and OEx. Plasma membranes were isolated from control and MIS muscles of mixed fiber types. MIS significantly increased glucose transport (3.4- and 2.8-fold) in LSed and OSed, respectively. MIS significantly increased glucose transporter number (2.5-fold) in LSed, but there was no increase in glucose transporter number in OSed. Peak oxygen uptake and citrate synthase activity were increased a similar amount for LEx and OEx groups, demonstrating a similar training stimulus. MIS significantly and similarly increased glucose transport in LEx and OEx (4.4- and 5.1-fold, respectively). The effects of MIS on plasma membrane glucose transporter number in the exercise-trained rats were similar to the responses observed in the sedentary lean and obese groups. MIS significantly increased glucose transporter number (2.6-fold) in LEx, whereas there was no increase in glucose transporter number in OEx. The reduction in MIS glucose transport in OSed appears to be related to a defect in the processes associated with the translocation of glucose transporters to the plasma membrane. Exercise training of the obese rats apparently did not alter this defect. Similar increases in peak oxygen uptake, citrate synthase, and MIS glucose transport in LEx and OEx groups suggest that insulin resistance does not limit the ability of the glucose transport system to adapt to exercise training in the obese male SHHF/ Mcc-fa cprats.

scholarly journals Exofacial photolabelling of the human erythrocyte glucose transporter with an azitrifluoroethylbenzoyl-substituted bismannose

1990 ◽  
Vol 269 (3) ◽  
pp. 615-622 ◽  
Author(s):  
A E Clark ◽  
G D Holman
Keyword(s):  
Transport System ◽  
Human Erythrocyte ◽  
Glucose Transporter ◽  
Erythrocyte Membranes ◽  
Trypsin Treatment ◽  
Intact Cells ◽  
Tryptic Fragment ◽  
System A ◽  
Glucose Transport System ◽  
Peptide Antibody

The synthesis of 2-N-[4-(1′-azitrifluoroethyl)benzoyl]-1,3-bis-(D-mannos-4-++ +yloxy)-2- propylamine (ATB-BMPA) is described. This compound was used as an exofacial probe for the human erythrocyte glucose-transport system. A new method is described for directly estimating the affinity for exofacial ligands which bind to the erythrocyte glucose transporter. By using this equilibrium-binding method, the Ki for ATB-BMPA was found to be 338 +/- 37 microM at 0 degrees C and 368 +/- 59 microM at 20 degrees C. This was similar to the concentration of ATB-BMPA required to half-maximally inhibit D-galactose uptake (Ki = 297 +/- 53 microM). The new photoaffinity reagent labelled the glucose transporter in intact cells but, because of its improved selectivity, was also used to label the glucose transporter in isolated erythrocyte membranes. The ATB-BMPA-labelled glucose transporter was 80% immunoprecipitated by anti-(GLUT1-C-terminal peptide) antibody, which shows that the GLUT1 glucose transporter is the major isoform present in erythrocytes. The labelling of the glucose transporter at its exofacial site, and the adoption of an outward-facing conformation, renders the transport system resistant to thermolysin and trypsin treatment. Trypsin treatment of the unlabelled glucose transporter in erythrocyte membranes produced an 18 kDa fragment which was subsequently labelled by ATB-BMPA, but had low affinity for this exofacial ligand. This suggests that the trypsin-treated transporter adopts an inward-facing conformation. The ability of D-glucose to displace ATB-BMPA from the native transporter and from the 18 kDa trypsin fragment have been compared. The D-glucose concentration which was required to obtain half-maximal inhibition of ATB-BMPA labelling was 6-fold lower for the 18 kDa tryptic fragment.

scholarly journals Testing transport models and transport data by means of kinetic rejection criteria

1989 ◽  
Vol 260 (3) ◽  
pp. 885-891 ◽  
Author(s):  
R M Krupka
Keyword(s):  
Experimental Data ◽  
Kinetic Analysis ◽  
Glucose Transport ◽  
Transport System ◽  
Reaction Scheme ◽  
Transport Systems ◽  
Choline Transport ◽  
Carrier Model ◽  
Glucose Transport System ◽  
General Relations

In the case of a transport system obeying Michaelis-Menten kinetics, completely general relationships are shown to exist between the final ratio of internal and external substrate concentrations, alpha, and the V/Km ratios found in zero-trans-entry, zero-trans-exit and equilibrium-exchange experiments (where V is a maximum substrate flux and Km a substrate half-saturation constant). The proof depends on a new method of derivation proceeding from the form of the experimental data rather than, as has been the practice in kinetic analysis, from a hypothetical reaction scheme. These general relationships, which will be true of all mechanisms giving rise to a particular type of behaviour (here Michaelis-Menten kinetics), provide a test for internal consistency in a set of experimental data. Other relationships, which are specific, can be derived from individual reaction schemes, with the use of traditional procedures in kinetic analysis. The specific relationships include constants for infinite trans entry and exit in addition to constants involved in the general relationships. In conjunction, the general and specific relationships provide a stringent test of mechanism. A set of results that fails to satisfy the general relationships must be rejected; here systematic error or unexpected changes in the transport system in different experiments may have distorted the calculated constants, or the system may not actually obey Michaelis-Menten kinetics. Results in accord with the general relationships, on the other hand, can be applied in specific tests of mechanism. The usefulness of the theorem is illustrated in the cases of the glucose-transport and choline-transport systems of erythrocytes. Experimental results taken from several studies in the literature, which were in accord with hyperbolic substrate kinetics, had previously been shown to disagree with relationships derived for the carrier model, and the model was rejected. The new analysis shows that the data violated the general relationships and therefore cannot decide the issue. More recent results on the glucose-transport system satisfy the general relations and agree with the carrier model.

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