Myo-Inositol transport in Klebsiella aerogenes. scyllo-Inositol, a non-metabolizable substrate for the study of the myo-inositol transport system.

1. Scyllo-Inositol is transported against a concentration gradient by Klebsiella aerogenes, but is not metabolized. 2. The apparent KT of scyllo-inositol is 0.05 X 10(-3) M while that of myo-inositol is 0.23 X 10(-3) M. The V values are respectively 32 and 12 nmol min(-1) mg cells(-1) (dry weight). 3. Both cyclitols bind to the same carrier, since typical competitive inhibition kinetics are observed. 4. Neither phosphoenolpyruvate phosphotransferase nor a periplasmic binding protein seems to be involved in the scyllo-inositol transport system. 5. The induction of the transport system is not repressed by malate, furmarate, citrate, succinate or pyruvate; however, acetate represses the induction. The activity of the transport system is increased when the growth medium is supplemented with adenosine 3':5'-monophosphate.     

Evidence for amino-acid: proton cotransport in Ricinus cotyledons

During germination and early growth of the castor-bean (Ricinus communis L.), protein in the endosperm is hydrolyzed and the amino acids are transferred into the cotyledons and then via the translocation stream to the axis of the growing seedling. The cotyledons retain the ability to absorb amino acids after removal of the endosperm and hypocotyl, exhibiting rates of transport up to 70 mol g^-1 h^-1. The transport of L-glutamine was not altered by KCl or NaCl in low concentrations (0–20 mM). High concentrations of KCl (100 mM) inhibited transport, presumably by decreasing the membrane potential. An increase in the pH of the medium bathing the cotyledons was observed for 10 min following addition of L-glutamine but not with D-glutamine, which is not transported. The rate of proton uptake was dependent on the concentration of L-glutamine in the external solution. Inhibitors and uncouplers of respiration (azide, 2, 4-dinitrophenol, carbonyl cyanide phenylhydrazone and N-ethylmaleimide) inhibited both L-glutamine uptake and L-glutamine-induced proton uptake. Amino acids other than L-glutamine also caused a transient pH rise and the rate of proton uptake was proportional to the rate of amino-acid uptake. The stoichiometry was 0.3 protons per amino acid transported. Addition of sucrose also caused proton uptake but the alkalisation by sucrose and by amino acids were not additive. Nevertheless, when sucrose was added 60 min after providing L-glutamine at levels saturating its uptake system, a rise in pH was again observed. The results were consistent with amino-acid transport and sucrose transport in castor-bean cotyledons both occurring by a proton cotransport in the same membrane system but involving separate carriers.     

The influx of calcium ions into human erythrocytes during cold storage

1. When human erythrocytes, suspended in iso-osmotic sucrose containing CaCl(2), are stored at 3 degrees C, Ca(2+) influx into the cells occurs. Simultaneously, efflux of K(+), Na(+), Cl(-) and water takes place and cell volume diminishes. 2. The extent of Ca(2+) influx increases with duration of cold storage and with increasing concentration of Ca(2+) in the suspending medium. 3. Erythrocytes that have been thus loaded with Ca(2+) exhibit Ca(2+) efflux against a concentration gradient when subsequently incubated at 37 degrees C. 4. Ca(2+) influx likewise occurs when the sucrose of the medium is replaced by iso-osmotic solutions of other non-ionized compounds. 5. Replacement of sucrose by iso-osmotic KCl or NaCl greatly diminishes the rate of Ca(2+) influx during cold storage; however, in iso-osmotic choline chloride, Ca(2+) influx is as rapid as in sucrose. 6. Preincubation of erythrocytes in iso-osmotic sucrose at 37 degrees C causes rapid efflux of K(+) and Na(+) and renders the cell membranes highly permeable to Ca(2+) during subsequent cold storage. 7. Preincubation of erythrocytes in iso-osmotic NaCl at 37 degrees C with trypsin or neuraminidase is without effect on the permeability of the membrane towards Ca(2+). 8. The experimental results lead to the conclusion that the main prerequisite for Ca(2+) influx into erythrocytes is the partial depletion of the cells of their univalent cations.     

Transport of phosphoenolpyruvate through red cell membrane in acidified isotonic sucrose medium.

Organic phosphate compounds added exogenously are impermeable to the red cell membrane in physiological conditions. However, when the cells were incubated in an acidified iso-osmotic sucrose medium(pH 4.2), phosphoenolpyruvate passed freely the membrane, though other glycolytic intermediates and nucleotides failed to permeate the membrane. During incubation of the PEP loaded red cells,PEP was metabolized rapidly and almost one-to-one stoichiometry was observed in the relationship between 2,3DPG production and PEP depletion.     

Characteristics of Sucrose Transport and Sucrose-Induced H+ Transport on the Tonoplast of Red Beet (Beta vulgaris L.) Storage Tissue

Sucrose-induced changes of the energization state of the red beet root (Beta vulgaris L. ssp. conditiva) vacuolar membrane were observed with the fluorescent dyes 6-chloro-9-{[4-(diethylamino)- 1-methylbutyl]-amino}-2-methoxyacridine dihydrochloride, as a pH monitor, and 9-amino-6-chloro-2-methoxyacridine (ACMA). Consequently, transient acidification of the surrounding suspension medium could be measured with a pH electrode. This signal was specific for Suc and was not seen for sorbitol, mannitol, or maltose. Sucrose-induced medium acidification was sensitive to the same inhibitors that were efficient in inhibiting sucrose transport, including the monoclonal antibodies TNP56-12 and C50-5-3. It was seen with vacuoles and vesicles energized with MgATP before sucrose was added but also with vacuoles not artificially energized previously. Using bafilomycin A1 for the inhibition of the vacuolar ATPase of vacuoles previously energized by MgATP, apparent Km values for H+ export from the vacuoles to the medium could be calculated taking into account the passive proton leak. Apparent Km values for H+ export determined from data obtained with pH measurements in the medium and with ACMA corresponded to those obtained previously for sucrose uptake. Comparing sucrose uptake rates with corresponding H+ export rates at the respective sucrose concentrations and at Km, a stoichiometry of approximately one proton per transported sucrose was estimated.     

Accumulation of phosphoenolpyruvate in red cells incubated with the phosphate ester in an acidified isotonic sucrose medium.

Accumulation of exogenous phosphoenolpyruvate against the concentration gradient was observed when human red cells were incubated in an acidified isotonic sucrose medium. Fluoride increased the apparent accumulation by inhibition of the intracellular metabolic interconversion of the phosphate compound. The accumulation appeared to be specific for phosphoenolpyruvate and the accumulation rate for 3-phosphoglycerate, which has a molecular size and pKa similar to those of phosphoenolpyruvate, was less than one-tenth of the rate of phosphoenolpyruvate. Red cells incubated in the acidified sucrose medium tended to adhere to each other when examined with a scanning electron microscope.     

The influx of calcium ions into human erythrocytes during cold storage. The influences of extracellular pH, intracellular adenosine triphosphate and efflux of univalent cations

1. When human erythrocytes are stored at 3 degrees C for several days as a suspension in iso-osmotic sucrose or KCl, containing CaCl(2), the rates of cellular ATP degradation are similar. 2. During cold storage of erythrocytes in sucrose-CaCl(2) medium, Ca(2+) influx and univalent-cation efflux occur, the pH value of the suspending medium rises and the intracellular pH falls. These pH changes correlate reasonably well with alterations in the membrane potential calculated from Cl(-) distribution. 3. The presence of Ca(2+) in the medium does not increase the rate of univalent-cation efflux from the cells. 4. When the pH of the medium is raised by addition of buffers, the rates of both Ca(2+) influx and univalent-cation efflux increase. 5. Replacement of sucrose by KCl as the main osmotic component of the medium completely suppresses Ca(2+) influx and univalent-cation efflux, although the pH of the KCl medium is higher than that of the sucrose medium. 6. When sucrose is replaced by choline chloride, Ca(2+) influx and univalent-cation efflux still occur, and the pH of the medium is similar to that found in iso-osmotic KCl. 7. When valinomycin, Pb(2+) or Cd(2+) are added to the iso-osmotic sucrose medium, the rate of efflux of univalent cations increases as also does the influx of Ca(2+). 8. From these and other observations, it was concluded that it is univalent-cation efflux rather than ATP depletion or elevated extracellular pH which is the prerequisite for Ca(2+) influx during cold storage.     

Turgor-sensitive sucrose and amino acid transport into developing seeds of Pisum sativum. Effect of a high sucrose or mannitol concentration in experiments with empty ovules

Sugar and amino acid transport into empty ovules of Pisum sativum L. cv. Marzia was examined. In fruits containing 4–6 developing seeds, the embryo was removed from four ovules. After this surgical treatment, each empty seed coat was filled with a solution (pH 5.5) containing a low (0, 50 or 200 m M ), medium (350, 400 or 500 m M ) or high (0.7 or 1 M ) concentration of sucrose and/or mannitol. In pulse-labelling experiments with sucrose and α-aminoisobutyric acid (AIB), transport of sucrose and AIB into an empty ovule filled with a solution containing a high sucrose concentration was the same as transport into an ovule filled with a mannitol solution of similar osmolarity, demonstrating that a high sucrose concentration in the seed coat apoplast affects phloem transport of sucrose and AIB into the seed coat only by the osmotic effect. The osmolarity of a given solution filling the seed coat cavity appeared to be important for phloem transport of sucrose and AIB into empty ovules.
In our experiments, 350 m M appeared to be the optimal concentration for sucrose and AIB transport into the cavity within an empty ovule, giving results comparable with transport into intact ovules. A lower osmolarity of the solution induced less transport. Very high sucrose or mannitol concentrations caused a strong inhibition of sucrose and AIB unloading from the seed coat, so that transport into the empty ovules was inhibited. A low (strongly negative) but not too low osmotic potential of the solution in the seed coat apoplast seems necessary to maintain a normal rate of phloem transport into developing seeds. Apparently, the "sink strength" of developing seeds is turgor-sensitive.     

Carbohydrate Utilization in Lactobacillus sake

The ability of Lactobacillus sake to use various carbon sources was investigated. For this purpose we developed a chemically defined medium allowing growth of L. sake and some related lactobacilli. This medium was used to determine growth rates on various carbohydrates and some nutritional requirements of L. sake. Mutants resistant to 2-deoxy-d-glucose (a nonmetabolizable glucose analog) were isolated. One mutant unable to grow on mannose and one mutant deficient in growth on mannose, fructose, and sucrose were studied by determining growth characteristics and carbohydrate uptake and phosphorylation rates. We show here that sucrose, fructose, mannose, N-acetylglucosamine, and glucose are transported and phosphorylated by the phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS). The PTS permease specific for mannose, enzyme II(supMan), was shown to be responsible for mannose, glucose, and N-acetylglucosamine transport. A second, non-PTS system, which was responsible for glucose transport, was demonstrated. Subsequent glucose metabolism involved an ATP-dependent phosphorylation. Ribose and gluconate were transported by PTS-independent permeases.     

等渗NaCL和KCL胁迫对高梁幼苗生长和气体交换的影响

本文比较研究了等渗NaCl和KCl胁迫下,高粱幼苗生长及叶片离子含量、质膜相对透性和有关气体交换参数的变化。结果表明,在低浓度NaCl和KCl胁迫7天时,高粱生长、含水量和质膜相对透性与对照相比没有明显变化,而净光合速率、蒸腾速率和气孔导度已明显下降,叶肉细胞间隙CO2浓度明显增加。NaCl胁迫下叶片Na+含量成倍增加,而K+和Ca2+含量无明显变化。KCl胁迫时叶片K+含量明显增加,Ca2+含量明显下降,而Na+含量没有明显变化。随着NaCl或KCl浓度的增加,幼苗生长和叶片含水量明显下降,质膜透性和细胞间隙CO2浓度明显增加,净光合速率、蒸腾速率和气孔导度进一步下降。 NaCl胁迫下叶片Na+含量进一步增加,K+和Ca2+进一步下降,而KCl胁迫下叶片K+含量进一步 增加,Na+和Ca2+含量进一步下降。KCl对高粱生长抑制、质膜透性、Ca2+含量下降及光合气体交换参数的影响均明显大于等渗的NaCl。     

Atrium contributes to osmoregulation in eels acclimated to sea water

Since highly concentrated NaCl is suspected to enter into the heart of the seawater eels, effects of high NaCl concentration on the atrial beating was examined, and plasma ion concentrations and osmolality were measured simultaneously in the blood collected from the bulbus arteriosus and from the caudal vessels. When 100 mmole l(-1) NaCl was added to the incubation medium, atrial contraction was enhanced significantly. Similar enhancement in the atrial contractility was also observed after addition of NaCH3SO4 (100 mmole l(-1)) or Tris HCl (100 mmole l(-1)), indicating that Na(+) and Cl(-) are not indispensable for the positive inotropic effect. Furthermore, an addition of sucrose (200 mmole l(-1)) also enhanced the contraction. Inversely, hypoosmotic solution reduced the atrial contraction. These results indicate that the eel atrium is sensitive to environmental osmolarity. The eel atrium responses even at 20 mmole l(-1) sucrose. Such an inotropic effect of sucrose was not depressed after blocking adrenoceptor with betaxolol, a beta1-adrenoceptor antagonist, indicating that the effect is not due to adrenaline release from nerve endings. Plasma osmolality and Na(+) concentration were higher in bulbus arteriosus than in caudal vessels, indicating that the eel heart is really exposed to hyperosmotic blood in sea water. The osmotically enhanced atrial contraction may increase the cardiac outflow into the gill. Such property of the atrium would have clear advantages for seawater teleosts, since the concentrated NaCl from the esophagus can be excreted immediately through the gill, without circulating their body, and blood homeostasis can be maintained efficiently.     

Sulfate transport in human lung fibroblasts (IMR-90)

Sulfate transport in a fibroblast cell line derived from human lung (IMR-90) occurred mainly via high- and low-affinity, SITS-sensitive pathways and to a lesser extent by an SITS-insensitive mechanism. In low-ionic-strength media (sucrose substituted for salts) the apparent Km of the carrier-mediated sulfate influx was 1 mM. At 0.3 mM, the sulfate concentration normally found in human serum, the contribution of the SITS-insensitive pathway was negligible. In physiological salts solution, an SITS-sensitive, high-affinity (Km 34 +/- 14 microM) sulfate influx system was observed at extracellular sulfate concentrations less than 100 microM. Between 100 and 500 microM sulfate, the range normally found in human serum, sulfate influx occurred via an SITS-sensitive, low-affinity pathway and to a small extent by an SITS-insensitive mechanism. Extracellular chloride inhibited the influx and stimulated the efflux of sulfate. Bicarbonate and thiosulfate inhibited sulfate influx but had no effect on sulfate efflux. Phosphate, arsenate, or Na+ did not affect sulfate uptake. These results indicate that in human lung fibroblast IMR-90 cells sulfate is transported mainly via an SO4(2-)/Cl- exchange system independent of the phosphate or Na+ transport. Since sulfate concentration as high as 50 mM only slightly increased sulfate efflux, SO4(2-)/SO4(2-) exchange is probably a minor component of sulfate uptake.     

Selection of NaCI Tolerant Calli and Regeneration of Plants in Maize

The embryonic calli produced from immature embryos of inbred “Huangzhao-4” of maize, that had been maintained for half a year, were transferred to media supplemented with different NaC1 concentrations (5, 10, 15, 20, 25, 30g/L) for callus selection. NaCl tolerant calli were established through three generations of selections. The growth and frequency of survival calli were affected significantly by NaCl concentration. The proliferetion of NaCl-tolerant calli was relatively good on medium containing of 10g/L NaC1. From these calli, plant lets could be produced on differentiation medium. On medium supplemented with 10g/L of NaC1 the plantlets could normally grow to transplantation. In NaCl-tolerant calli cultured on medium containing 10g/L of NaC1, the contents of free amino acids, free proline, Na+, K+ were 18.0%,87.3%,661.9%,25.5% respectively higher than those in un-selected calli grown on subculture medium, but Ca2+ content decreased significantly. On medium containing 10g/L of NaC1, cells and their organelles in NaCl-tolerant calli had normal morphology and structure, and vigorous metabolism, but in un-selected calli, the majority of cells turned to wards dying. Although tolerant plants regenerated and their filial ones had grown in non-salted soil, their progenies retained the property tolerance, but showed segregation of the degrees of tolerance. In 10g/L NaC1 solution, the seeds of progenies from one plant regenerated could germinate normally, and grow into healthy seedlings. Therefore, the NaCl-tolerant calli and plantlets that we have obtained NaCl-tolerant variants.     

Abolition of crypticity of Arthrobacter pyridinolis toward glucose and alpha-glucosides by tricarboxylic acid cycle intermediates

Arthrobacter pyridinolis cannot grow on glucose as sole carbon source, although the cells possess catabolic enzymes of the Embden-Meyerhof and pentose phosphate pathways as well as a complete tricarboxylic acid cycle. Crypticity toward glucose is abolished by a period of growth in a medium containing malate, succinate, citrate, or fumarate in addition to glucose. Other carbon sources, which support as rapid growth as does malate (e.g. asparagine), do not enable the cells to use glucose. Malate, succinate, citrate, and fumarate abolish crypticity toward glucose only in the second phase of diauxic growth after the tricarboxylic acid cycle intermediate has been depleted. This sequence of events, first observed in growth curves, has been verified by experiments in which the incorporation of radioactive substrates into trichloroacetic acid-insoluble cellular material was followed. The tricarboxylic acid cycle intermediates which confer the ability to utilize glucose also enhance the utilization of the alphaglucosides sucrose and maltose. The mechanism whereby growth on certain tricarboxylic acid cycle intermediates confers the subsequent ability to grow on glucose is related to a transport system for glucose and alpha-glucosides. This transport system has been assayed by measuring the uptake of [1-(14)C]-2-deoxyglucose. Cells grown for varying periods of time in asparagine, asparagine plus glucose, or malate do not transport 2-deoxyglucose. Cells from malate-glucose cultures that are in the exponential phase of growth on glucose can transport 2-deoxyglucose. Transport of 2-deoxyglucose shows Michaelis-Menten kinetics with a K(m) of 2.9 x 10(-4) M. It is competitively inhibited by glucose, alpha-methylglucopyranoside, and maltose. The transport of 2-deoxyglucose is inhibited by cyanide, dinitrophenol, azide, and N-ethylmaleimide, but not by malonate or fluoride. No phosphoenolpyruvate: d-glucose phosphotransferase activity has been detected, and the 2-deoxyglucose transported into the cell is not phosphorylated.     

Cellobiose transport by mixed ruminal bacteria from a Cow.

The transport of cellobiose in mixed ruminal bacteria harvested from a holstein cow fed an Italian ryegrass hay was determined in the presence of nojirimycin-1-sulfate, which almost inhibited cellobiase activity. The kinetic parameters of cellobiose uptake were 14 microM for the Km and 10 nmol/min/mg of protein for the Vmax. Extracellular and cell-associated cellobiases were detected in the rumen, with both showing higher Vmax values and lower affinities than those determined for cellobiose transport. The proportion of cellobiose that was directly transported before it was extracellularly degraded into glucose increased as the cellobiose concentration decreased, reaching more than 20% at the actually observed levels of cellobiose in the rumen, which were less than 0.02 mM. The inhibitor experiment showed that cellobiose was incorporated into the cells mainly by the phosphoenolpyruvate phosphotransferase system and partially by an ATP-dependent and proton-motive-force-independent active transport system. This finding was also supported by determinations of phosphoenolpyruvate phosphotransferase-dependent NADH oxidation with cellobiose and the effects of artificial potentials on cellobiose transport. Cellobiose uptake was sensitive to a decrease in pH (especially below 6.0), and it was weakly but significantly inhibited in the presence of glucose.     

Evidence for the involvement of a UDP-glucose-dependent group translocator in sucrose uptake into vacuoles of storage roots of red beet

Vacuoles isolated from the storage roots of red beet (Beta vulgaris L.) accumulate sucrose via two different mechanisms. One mechanism transports sucrose directly, and its rate is increased by the addition of MgATP. The other mechanism utilizes uridine diphosphate glucose (UDP-glucose) to synthesize and simultaneously transport sucrose phosphate and sucrose into the vacuole. This group translocation mechanism has also been found in sugarcane vacuoles. As in sugarcane, the beet group translocator does not require fructose 6-phosphate, nor is the latter substance transported into the vacuole. The uptake of UDP[¹⁴C]glucose in inhibited by high concentrations of osmoticum.Abbreviations EDTA ethylenediaminetetraacetic acid - Hepes 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid - UDP uridine 5-diphosphate     

Induction of amino acid transport activity in chick embryo fibroblasts by replacement of extracellular sodium chloride with disaccharide

The activity of amino acid transport System A in avian fibroblasts was increased following incubation of the cells in a medium in which most of the NaCl normally present had been isoosmotically replaced by sucrose. This increase was detectable after 2 h of incubation, reached a maximum at about 4 h, and remained constant thereafter. Transfer of treated cells back to a normal medium resulted in decay of the induced transport activity, with a half-life of less than 2 h. Kinetic analysis revealed that the increase in transport activity arose from an increase in Vmax, with little change in Km. This induction of System A activity did not occur if an inhibitor of either RNA or protein synthesis was present in the modified medium. The use of various different solutes as replacements for NaCl in the incubation medium showed that, although each replacement caused a decrease in both cellular Na+ content and protein synthesis, only disaccharides produced the increase in amino acid transport activity. In addition, estimates of cell volume indicated that, even under iso-osmotic conditions, incubation in the sucrose-containing medium caused initial cell shrinkage, followed by swelling. It is concluded that this induction of System A activity is associated with a volume regulatory process and that this process probably accounts for the parallel responses previously observed when cells were incubated in hyperosmolar media. Induction of amino acid transport activity by this process is distinct from adaptive regulation, caused by amino acid starvation; but the two processes are not strictly additive, and so appear to converge at some step.     

Glucose Transport in Brucella abortus

Brucella abortus British strain 19 transported glucose with an apparent K(m) of 0.16 mM and an apparent V(max) of 250 nmol per min per mg of N. The only common glucose analogue transported was 2-deoxyglucose (2-DOG), with an apparent K(i) of 0.73 mM. Alpha- or beta-methyl glucosides and 3-O-methylglucose were not transported. Transport was linear for 70 to 90 s, depending on the concentration of substrate used. 2-Deoxyglucose was transported as the free sugar and was not further metabolized once inside the cell. There was no glucose phosphoenolpyruvate phosphotransferase system (PEP-PTS) present, and there were no inhibitors present in Brucella cell-free extract that inhibited the Escherichia coli glucose PEP-PTS. N-Ethylmaleimide (NEM) and p-chloromercuribenzoate (pCMB) completely inhibited transport of glucose and 2-DOG. Glutathione, dithiothreitol, and beta-mercaptoethanol reversed the effects of pCMB but not of NEM. A pH optimum of 7.2 and a temperature optimum of 37 to 45 C were observed for both K(m) and V(max). The glucose transport system appeared to be constitutive for glucose transport in cells grown on fructose, galactose, erythritol, or glucose. The electron transfer inhibitors carbonyl cyanide, m-chlorophenylhydrazone, NaN(3), 2,4-dinitrophenol, and KCN inhibited 2-DOG transport to a greater extent than did the metabolic energy inhibitors NaAsO(4), iodoacetate, KF, and 2-heptyl-4-hydroxyquinoline-N-oxide. Dicyclohexylcarbodiimide, an inhibitor of membrane-bound adenosine triphosphatases, inhibited transport by 100%.     

Glycine betaine transport in Escherichia coli: osmotic modulation.

Exogenous glycine betaine highly stimulates the growth rate of various members of the Enterobacteriaceae, including Escherichia coli, in media with high salt concentrations (D. Le Rudulier and L. Bouillard, Appl. Environ. Microbiol. 46:152-159, 1983). In a nitrogen- and carbon-free medium, glycine betaine did not support the growth of E. coli either on low-salt or high-salt media. This molecule was taken up by the cells but was not catabolized. High levels of glycine betaine transport occurred when the cells were grown in media of elevated osmotic strength, whereas relatively low activity was found when the cells were grown in minimal medium. A variety of electrolytes, such as NaCl, KCl, NaH2PO4, K2HPO4, K2SO4, and nonelectrolytes like sucrose, raffinose, and inositol triggered the uptake of glycine betaine. Furthermore, in cells subjected to a sudden osmotic upshock, glycine betaine uptake showed a sixfold stimulation 30 min after the addition of NaCl. Part of this stimulation might be a consequence of protein synthesis. The transport of glycine betaine was energy dependent and occurred against a concentration gradient. 2,4-Dinitrophenol almost totally abolished the glycine betaine uptake. Azide and arsenate exerted only a small inhibition. In addition, N,N'-dicyclohexylcarbodiimide had a very low inhibitory effect at 1 mM. These results indicated that glycine betaine transport is driven by the electrochemical proton gradient. The kinetics of glycine betaine entry followed the Michaelis-Menten relationship, yielding a Km of 35 microM and a Vmax of 42 nmol min-1 mg of protein-1. Glycine betaine transport showed considerable structural specificity. The only potent competitor was proline betaine when added to the assay mixtures at 20-fold the glycine betaine concentration. From these results, it is proposed that E. coli possesses an active and specific glycine betaine transport system which is regulated by the osmotic strength of the growth medium.     

Mechanisms of sugar transport byThiobacillus A2

Comparison of the effects of uncoupling agents, arsenate, fluoride and cyanide on sugar transport byThiobacillus A2 indicated that (a) glucose uptake by fast-growing strain GFI involved a high energy phosphate dependent system; (b) transport of glucose by the wild type and of fructose and sucrose by both strains, was by respiration dependent systems requiring a membrane proton gradient. Glucose and sucrose were competitive inhibitors of the transport of each other. Bacteria grown on glucose +sucrose (20+2 mM) transported glucose much faster than those grown on glucose alone. This could explain the great stimulation of growth rate on glucose, in the presence of sucrose.Abbreviations Butyl PBD 2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole - DBP 2,4-dibromophenol - DNP 2,4-dinitrophenol - FCCP carboxylcyanide p-trifluoromethoxyphenylhydrazone - 3-OMG 3-O-methylglucose - PCP pentachlorophenol - Tris tris(Hydroxymethyl)-aminomethane - TTFB 4,5,6,7-tetrachloro-2-trifluoromethylbenzimidazole - PEP phosphoenolpyruvate