scholarly journals The Hexose-Proton Cotransport System of Chlorella

1974 ◽  
Vol 64 (5) ◽  
pp. 568-581 ◽  
Author(s):  
Ewald Komor ◽  
Widmar Tanner
Keyword(s):  
Sugar Transport ◽  
Protonated Form ◽  
Weak Acid ◽  
Sugar Uptake ◽  
Sugar Accumulation ◽  
Maximal Velocity ◽  
Uptake System ◽  
High Affinity ◽  
Ph Values ◽  
Proton Concentration

The proton concentration in the medium affects the maximal velocity of sugar uptake with a Km of 0.3 mM (high affinity uptake). By decreasing the proton concentration a decrease in high affinity sugar uptake is observed, in parallel the activity of a low affinity uptake system (Km of 50 mM) rises. Both systems add up to 100%. The existence of the carrier in two conformational states (protonated and unprotonated) has been proposed therefore, the protonated form with high affinity to 6-deoxyglucose, the unprotonated form with low affinity. A plot of extrapolated Vmax values at low substrate concentration versus proton concentration results in a Km for protons of 0.14 µM, i.e. half-maximal protonation of the carrier is achieved at pH 6.85. The stoichiometry of protons cotransported per 6-deoxyglucose is close to 1 at pH 6.0–6.5. At higher pH values the stoichiometry continuously decreases; at pH 8.0 only one proton is cotransported per four molecules of sugar. Whereas the translocation of the protonated carrier is strictly dependent on sugar this coupling is less strict for the unprotonated form. Therefore at alkaline pH a considerable net efflux of accumulated sugar can occur. The dependence of sugar accumulation on pH has been measured. The decrease in accumulation with higher pH values can quantitatively be explained by the decrease in the amount of protonated carrier. The properties of the unprotonated carrier resemble strikingly the properties of carrier at the inner side of the membrane. The inside pH of Chlorella was measured with the weak acid 5,5-dimethyl-2, 4-oxazolidinedion (DMO). At an outside pH of 6.5 the internal pH was found to be 7.2. To explain the extent of sugar accumulation it has to be assumed that the membrane potential also contributes to active sugar transport in this alga.

scholarly journals Dihydrocytochalasin B. Biological effects and binding to 3T3 cells.

1978 ◽  
Vol 76 (2) ◽  
pp. 360-370 ◽  
Author(s):  
S J Atlas ◽  
S Lin
Keyword(s):  
Cell Motility ◽  
Morphological Changes ◽  
Biological Effects ◽  
Sugar Transport ◽  
Sugar Uptake ◽  
3T3 Cells ◽  
Binding Studies ◽  
High Affinity ◽  
Undetermined Function ◽  
Induced Changes

Dihydrocytochalasin B (H2CB) does not inhibit sugar uptake in BALB/c 3T3 cells. Excess H2CB does not affect inhibition of sugar uptake by cytochalasin B (CB), indicating that it does not compete with CB for binding to high-affinity sites. As in the case of CB, H2CB inhibits cytokinesis and changes the morphology of the cells. These results demonstrate that the effects of CB on sugar transport and on cell motility and morphology involve separate and independent sites. Comparison of the effects of H2CB, CB, and cytochalasin D (CD) indicates that treatment of cells with any one of the compounds results in the same series of morphological changes; the cells undergo zeiosis and elongation at 2-4 microM CB and become arborized and rounded up at 10-50 microM CB. H2CB is slightly less potent than CB, whereas CD is five to eight times more potent than CB in causing a given state of morphological change. These results indicate that the cytochalasin-induced changes in cell morphology are mediated by a specific site(s) which can distinguish the subtle differences in the structures of the three compounds. Competitive binding studies indicate that excess H2CB displaces essentially all of the high-affinity bound [3H]CB, but, at less than 5 x 10(-5) M H2CB is not so efficient as unlabeled CB in the displacement reaction. In contrast, excess CD displaces up to 40% of the bound [3H]CB. These results suggest that three different classes of high-affinity CB binding sites exist in 3T3 cells: sites related to sugar transport, sites related to cell motility and morphology, and sites with undetermined function.

scholarly journals Dexamethasone inhibits the hexose monophosphate shunt in activated rat peritoneal macrophages by reducing hexokinase-dependent sugar uptake

1991 ◽  
Vol 278 (1) ◽  
pp. 129-135 ◽  
Author(s):  
R J Rist ◽  
R J Naftalin
Keyword(s):  
Sugar Transport ◽  
Peritoneal Macrophages ◽  
Free Sugar ◽  
Sugar Uptake ◽  
Sugar Accumulation ◽  
Dependent Manner ◽  
Hexose Monophosphate ◽  
Simultaneous Exposure ◽  
Hexose Monophosphate Shunt

Dexamethasone decreases 2-D-deoxyglucose (2-dGlc) uptake and accumulation into rat peritoneal macrophages in vitro in a concentration- and time-dependent manner (Ki for 1 microM-dexamethasone after a 2 h exposure = 0.71 +/- 0.21 microM; Ki for 0.1 microM-dexamethasone after exposure for 4 h = 0.10 +/- 0.06 microM). The inhibition of 2-dGlc uptake is consistent with a decrease in the coupling between endofacial hexokinase activity and the sugar transporter. The evidence for this is: (1) the Km for zero-trans 2-dGlc uptake in quiescent macrophages was increased by dexamethasone, but there was no significant effect on the Vmax.; (2) dexamethasone increased the rate of exit of sugar from cells preloaded with 2-dGlc; (3). the free sugar accumulation within the cytosol of the cells above the external solution concentration was significantly decreased by dexamethasone. These effects of dexamethasone on 2-dGlc transport were antagonized by simultaneous exposure to the steroid RU 38486 (Ki = 0.04 +/- 0.01 microM; 4 h incubation). Although dexamethasone inhibited zero-trans uptake, the maximum rate of infinite-trans exchange uptake of 2-dGlc into cells preloaded with 3-O-methyl-D-glucose (40 mM) was unaltered by dexamethasone or RU 38486, indicating that the dexamethasone-dependent decrease in zero-trans uptake was not due to a change in the number of transporters in the plasma membrane. Dexamethasone also inhibited the phorbol myristate acetate-induced stimulation of hexose monophosphate shunt (HMPS) activity, and this was reversed by RU 38486. Cytochalasin B, the potent sugar-transport inhibitor, inhibited HMPS activity and 2-d[2,6-3H]Glc uptake equally, indicating a single site of action. By contrast, dexamethasone showed differential inhibition of HMPS activity and 2-d[2,6-3H]Glc uptake, suggesting that it not only acts by decreasing the coupling between hexokinase and sugar transport, but also at one or more additional points.

scholarly journals Characterization of Streptococcus mutans Strains Deficient in EIIABMan of the Sugar Phosphotransferase System

2003 ◽  
Vol 69 (8) ◽  
pp. 4760-4769 ◽  
Author(s):  
Jacqueline Abranches ◽  
Yi-Ywan M. Chen ◽  
Robert A. Burne
Keyword(s):  
Streptococcus Mutans ◽  
Type Strain ◽  
Wild Type Strain ◽  
Sugar Transport ◽  
Fold Increase ◽  
Sugar Uptake ◽  
Uptake System ◽  
Oral Streptococci ◽  
Wild Type ◽  
Phosphotransferase System

ABSTRACT The phosphoenolpyruvate:sugar phosphotransferase system (PTS) is the major sugar uptake system in oral streptococci. The role of EIIABMan (encoded by manL) in gene regulation and sugar transport was investigated in Streptococcus mutans UA159. The manL knockout strain, JAM1, grew more slowly than the wild-type strain in glucose but grew faster in mannose and did not display diauxic growth, indicating that EIIABMan is involved in sugar uptake and in carbohydrate catabolite repression. PTS assays of JAM1, and of strains lacking the inducible (fruI) and constitutive (fruCD) EII fructose, revealed that S. mutans EIIABMan transported mannose and glucose and provided evidence that there was also a mannose-inducible or glucose-repressible mannose PTS. Additionally, there appears to be a fructose PTS that is different than FruI and FruCD. To determine whether EIIABMan controlled expression of the known virulence genes, glucosyltransferases (gtfBC) and fructosyltransferase (ftf) promoter fusions of these genes were established in the wild-type and EIIABMan-deficient strains. In the manL mutant, the level of chloramphenicol acetyltransferase activity expressed from the gtfBC promoter was up to threefold lower than that seen with the wild-type strain at pH 6 and 7, indicating that EIIABMan is required for optimal expression of gtfBC. No significant differences were observed between the mutant and the wild-type background in ftf regulation, with the exception that under glucose-limiting conditions at pH 7, the mutant exhibited a 2.1-fold increase in ftf expression. Two-dimensional gel analysis of batch-grown cells of the EIIABMan-deficient strain indicated that the expression of at least 38 proteins was altered compared to that seen with the wild-type strain, revealing that EIIABMan has a pleiotropic effect on gene expression.

scholarly journals Active transport of charged substrates by a proton/sugar co-transport system. Amino-sugar uptake in the yeast Rhodotorula gracilis

1981 ◽  
Vol 194 (2) ◽  
pp. 433-441 ◽  
Author(s):  
C Niemietz ◽  
R Hauer ◽  
M Höfer
Keyword(s):  
Membrane Potential ◽  
Amino Sugar ◽  
Protonated Form ◽  
Sugar Uptake ◽  
Amino Sugars ◽  
Maximal Velocity ◽  
Deprotonated Form ◽  
Half Saturation Constant ◽  
Carbonyl Cyanide ◽  
Rhodotorula Gracilis

1. In the yeast Rhodotorula gracilis several amino sugars were actively transported. Glucosamine, which is largely protonated at physiological pH (pK 7.75) was used as a model substrate. At pH 6.75 its half-saturation constant was 1 mM and the maximal velocity was 50 nmol/min per mg dry wt. 2. Amino sugars were taken up via the monosaccharide carrier. The transport of glucosamine was strongly restricted by monosaccharides. D-Xylose inhibited competitively the uptake of glucosamine. The inhibition constant was 1 mM. Cells preloaded with D-xylose showed exchange transport on subsequent addition of glucosamine. 3. Transport of glucosamine was energized by the membrane potential. Uncoupling agents such as carbonyl cyanide m-chlorophenyl-hydrazone and the lipophilic cation TPP+ (tetraphenylphosphonium ion) at concentrations that depolarized the membrane potential inhibited the uptake of glucosamine. Conversely the transport of glucosamine partly dissipated the membrane potential, which was monitored by radioactively labelled lipophilic cations. 4. The translocated charges were electrically compensated by the extrusion of protons and K+ (1 glucosamine molecule/0.85 H+ + 0.15 K+). 5. An increase of the pH in the range 4.75-8.75 lead to a decrease of the half-saturation constant from 5 mM to 1 mM and to an optimum of the maximal velocity at pH 6.75. We suggest that this fair constancy is due to the carrier not distinguishing between the protonated form of glucosamine (pH less than 7.75) and the deprotonated form (pH greater than 7.75). The increase of V(T) (maximal transport velocity) between pH 4.75 and 6.75 is due to the increase of the membrane potential: the decrease between pH 6.75 and 8.75 is due to the deprotonization of the carrier.

3,5,3′-Tri-iodothyronine enhances sugar transport in rat thymocytes by increasing the intrinsic activity of the plasma membrane sugar transporter

1990 ◽  
Vol 124 (1) ◽  
pp. 133-140 ◽  
Author(s):  
J. Segal ◽  
S. H. Ingbar
Keyword(s):  
Plasma Membrane ◽  
Cytochalasin B ◽  
Intact Cell ◽  
Binding Capacity ◽  
Sugar Transport ◽  
Intrinsic Activity ◽  
Sugar Uptake ◽  
Maximal Velocity ◽  
Single Class ◽  
Sugar Transporters

ABSTRACT We have shown that 3,5,3′-tri-iodothyronine (T3) produces a prompt increase in sugar transport in rat thymocytes by increasing the maximal velocity without changing the Michaelis–Menten constant of the plasma membrane sugar transport system. To elucidate further the mechanism of this effect, we have now assessed the influence of T3 on the number and affinity of sugar transporters in thymocytes, measured as the sugar (2-deoxyglucose; dGlc)-displaceable binding of cytochalasin B. Cytochalasin B inhibited in a dose-related manner the uptake of dGlc by rat thymocytes with inhibition constant values of 0·19 and 0·22 μmol/l in the presence and absence of T3 respectively. Binding of cytochalasin B by the sugar-displaceable sites was rapid and saturable, demonstrating a single class of sites having an apparent dissociation constant of 0·33 ± 0·02 (s.d.) μmol/l and maximal binding capacity of 3·73±0·48 pmol/20 × 106 cells (11·2±1·4 × 104 sites/thymocyte). In the rat thymocyte, sugar transporters were found to be located in two major subcellular pools, the plasma membrane and microsomes, the latter being about twice the size of the former. In these subcellular compartments, as well as in the intact cell, binding of [3H]cytochalasin B by the sugar-displaceable sites constituted about 40% of total cytochalasin B binding. 3,5,3′-Tri-iodothyronine in concentrations that stimulated uptake of dGlc by thymocytes had no effect on [3H]cytochalasin B binding (total and sugar-displaceable) in the intact cell and in the plasma membrane and microsomal compartments, nor did it influence the affinity and number of sugar transporters. From these observations we conclude that, in the rat thymocyte, T3 acts to increase sugar uptake by increasing the intrinsic activity, i.e. the efficiency, rather than the number of sugar transporters. Journal of Endocrinology (1990) 124, 133–140

scholarly journals Characterization of simultaneous uptake of xylose and glucose in Caldicellulosiruptor kronotskyensis for optimal hydrogen production

2021 ◽  
Vol 14 (1) ◽  
Author(s):  
Thitiwut Vongkampang ◽  
Krishnan Sreenivas ◽  
Jonathan Engvall ◽  
Carl Grey ◽  
Ed W. J. van Niel
Keyword(s):  
Glucose Uptake ◽  
Growth Patterns ◽  
Sugar Uptake ◽  
Uptake System ◽  
Sugar Mixtures ◽  
Xylose Uptake ◽  
Growth Profiles ◽  
High Concentrations ◽  
Xylose Transporter

Abstract Background Caldicellulosiruptor kronotskyensis has gained interest for its ability to grow on various lignocellulosic biomass. The aim of this study was to investigate the growth profiles of C. kronotskyensis in the presence of mixtures of glucose–xylose. Recently, we characterized a diauxic-like pattern for C. saccharolyticus on lignocellulosic sugar mixtures. In this study, we aimed to investigate further whether C. kronotskyensis has adapted to uptake glucose in the disaccharide form (cellobiose) rather than the monosaccharide (glucose). Results Interestingly, growth of C. kronotskyensis on glucose and xylose mixtures did not display diauxic-like growth patterns. Closer investigation revealed that, in contrast to C. saccharolyticus, C. kronotskyensis does not possess a second uptake system for glucose. Both C. saccharolyticus and C. kronotskyensis share the characteristics of preferring xylose over glucose. Growth on xylose was twice as fast (μmax = 0.57 h−1) as on glucose (μmax = 0.28 h−1). A study of the sugar uptake was made with different glucose–xylose ratios to find a kinetic relationship between the two sugars for transport into the cell. High concentrations of glucose inhibited xylose uptake and vice versa. The inhibition constants were estimated to be KI,glu = 0.01 cmol L−1 and KI,xyl = 0.001 cmol L−1, hence glucose uptake was more severely inhibited by xylose uptake. Bioinformatics analysis could not exclude that C. kronotskyensis possesses more than one transporter for glucose. As a next step it was investigated whether glucose uptake by C. kronotskyensis improved in the form of cellobiose. Indeed, cellobiose is taken up faster than glucose; nevertheless, the growth rate on each sugar remained similar. Conclusions C. kronotskyensis possesses a xylose transporter that might take up glucose at an inferior rate even in the absence of xylose. Alternatively, glucose can be taken up in the form of cellobiose, but growth performance is still inferior to growth on xylose. Therefore, we propose that the catabolism of C. kronotskyensis has adapted more strongly to pentose rather than hexose, thereby having obtained a specific survival edge in thermophilic lignocellulosic degradation communities.

Opportunistic heterotrophy in gametophytes of the homosporous fern Ceratopteris richardii

Botany ◽  
2009 ◽  
Vol 87 (8) ◽  
pp. 799-806 ◽  
Author(s):  
Deborah A. Alongi ◽  
Jeffrey P. Hill ◽  
Matthew J. Germino
Keyword(s):  
Sugar Transport ◽  
Light Limitation ◽  
Sugar Uptake ◽  
Growth Media ◽  
Ceratopteris Richardii ◽  
Glucose Depletion ◽  
Homosporous Fern ◽  
Preferential Uptake ◽  
Underlying Mechanisms ◽  
Exogenous Sugar

Fern gametophytes are extremely shade-tolerant, potentially existing for long periods under conditions of extreme light limitation. Many previous studies have demonstrated an increase in gametophyte growth and incidence of spontaneous transition to sporophyte morphology (apogamy) under culture on media containing exogenous sugar. However, these studies did not verify sugar uptake or quantify relative growth on media containing different sugar types. Here, we examine the extent of heterotrophy and underlying mechanisms of sugar transport in photosynthetic gametophytes of the fern Ceratopteris richardii Brongn. Exogenous sugar uptake, growth, and sugar transport were evaluated with assays of exogenous glucose depletion, experimental culture of gametophytes under different sugar and light conditions, and bioinformatic approaches. The glucose from the growth media was significantly depleted by gametophytes growing under all conditions, especially those in the dark compared with those exposed to higher light. Gametophyte area increased similarly when cultured on equimolar concentrations of either glucose or the disaccharide sucrose, likely due to preferential uptake of one of the monomers of sucrose. Although at least one gene with similarity to sucrose transporters is expressed in germinating spores, our results suggest a reliance on monosaccharide transport for exogenous sugar uptake. Glucose assimilation in both light and dark conditions constitutes nutritional opportunism and may enhance gametophyte survival in very low light.

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