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PubMed1990

Metabolism of intravenously administered maltose in renal tubules in humans.

To investigate how urinary excretion rates (UERs) of maltose and glucose are determined after intravenous maltose infusion, maltose and glucose solutions were infused at various rates and the relationships between UERs of maltose and glucose and their plasma concentrations were examined. Results showed the existence of a threshold plasma maltose concentration for the urinary excretions of maltose and glucose and the existence of a maximum rate of urinary glucose excretion after maltose infusion. Elevation of plasma glucose concentration by simultaneous glucose infusion increased urinary glucose excretion but did not increase urinary maltose excretion; the relationship between plasma total sugar concentration and urinary total sugar excretion was unchanged. Results suggest that maltose administered intravenously is hydrolyzed to glucose by maltase in renal tubules and reabsorbed as glucose competitively with glucose derived from plasma and that the maximum utilization of intravenously infused maltose is determined by the tubular glucose reabsorption capacity.

Adult↗
PubMed1976

Maltose transport in Escherichia coli K12. A comparison of transport kinetics in wild-type and lambda-resistant mutants as measured by fluorescence quenching.

The kinetic parameters for the maltose transport system in Escherichia coli K12 were determined with maltose and maltotriose as substrates. The system exhibits an apparent Km of 1 muM for maltose and 2 muM for maltotriose. The V of entry was determined as 2.0 and 1.1 nmol substrate/min per 10(8) cells. Mutations in lamB, the structural gene for the receptor protein of phage lambda, increased the Km for maltose transport by a factor of 100-500 without influencing the maximal rate of transport. Maltotriose is no longer transported in these lamB mutants. The maltose-binding protein, an essential component of the maltose transport system, was found to exhibit substrate-dependent fluorescence quenching. This phenomenon was used to determine dissociation constants and to estimate the rate of ligand dissociation. A Kd of 1 muM for maltose and of 0.16 muM for maltotroise was found. From the comparison of the kinetic parameters of transport of maltose and maltotriose in wild-type and lambda-resistant mutants with the binding constants for both sugars to purified maltose-binding protein, we conclude that the lambda receptor facilitates the diffusion of maltose and maltodextrins through the outer membrane.

Bacterial Proteins↗
PubMed1994

Mechanism of maltose uptake and glucose excretion in Lactobacillus sanfrancisco.

Lactobacillus sanfrancisco LTH 2581 can use only glucose and maltose as sources of metabolic energy. In maltose-metabolizing cells of L. sanfrancisco, approximately half of the internally generated glucose appears in the medium. The mechanisms of maltose (and glucose) uptake and glucose excretion have been investigated in cells and in membrane vesicles of L. sanfrancisco in which beef heart cytochrome c oxidase had been incorporated as a proton-motive-force-generating system. In the presence of ascorbate, N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD), and cytochrome c, the hybrid membranes facilitated maltose uptake against a concentration gradient, but accumulation of glucose could not be detected. Similarly, in intact cells of L. sanfrancisco, the nonmetabolizable glucose analog alpha-methylglucoside was taken up only to the equilibration level. Selective dissipation of the components of the proton and sodium motive force in the hybrid membranes indicated that maltose is transported by a proton symport mechanism. Internal [14C]maltose could be chased with external unlabeled maltose (homologous exchange), but heterologous maltose/glucose exchange could not be detected. Membrane vesicles of L. sanfrancisco also catalyzed glucose efflux and homologous glucose exchange. These activities could not be detected in membrane vesicles of glucose-grown cells. The results indicate that maltose-grown cells of L. sanfrancisco express a maltose-H+ symport and glucose uniport system. When maltose is the substrate, the formation of intracellular glucose can be more rapid than the subsequent metabolism, which leads to excretion of glucose via the uniport system.

Ascorbic Acid↗
PubMed1975

[Are maltose infusions suitable for infusion therapy].

The suitability of maltose for parenteral nutrition was investigated in metabolically healthy volunteers. A solution containing 20% of maltose was infused intravenously for four hours using three different doses (0.125 g/kg; 0.25 g/kg; 0.5 g/kg BW/h). Following cessation of the infusions the laboratory controls were carried on for four more hours. The infusions of maltose were tolerated without any complications. However, only when using the lowest dosage a steady state in blood concentration of maltose was reached, i.e. in the case of 0.125 g/kg BW/h. The results show that in humans the metabolic capacity for maltose is limited. The glucose concentration in blood remained almost unaltered during maltose infusion, while the serum insulin concentration was slightly elevated. A further sign for metabolism of maltose was the decrease in free fatty acid concentration. Because of the low metabolic capacity for maltose the urinary loss (in the form of maltose and glucose) is high with greater infusion rates and amounts to 20-30% of the intravenous load. A greater part of the sugar excreted in the urine consists of glucose, despite an almost normal blood glucose concentration. Considering the results of the experiments with volunteers it is concluded that maltose is not suited for intravenous therapy. Because of the low metabolic capacity of the human organism the renal losses are too great.

Adult↗
PubMed1989

beta-Glucose-1-Phosphate, a Possible Mediator for Polysaccharide Formation in Maltose-Assimilating Lactococcus lactis.

Homolactic fermentation of glucose and heterolactic fermentation of maltose with Lactococcus lactis 65.1 were confirmed. When moles of glucose were compared, the uptake rates of the two carbon sources were similar. The intracellular concentration of fructose-1,6-diphosphate (FDP) in maltose-assimilating cells was half of that in glucose-assimilating cells. Similarly, formation of FDP and lactate from maltose by extracts of maltose-grown cells was half of that formed from glucose by extracts of glucose-grown cells, indicating a difference in the utilization of the two carbon sources for energy metabolism. Concentrations of adenine nucleotides were similar in both types of cells. Glucose-1-phosphate was found in extracts of maltose-grown cells given maltose and, in addition, an inducible and low beta-specific phosphoglucomutase activity was observed. beta-Glucose-1-phosphate was not metabolized by cell extracts to either FDP or lactate, suggesting an alternative metabolic route. The amount of [C]maltose incorporated into the cell material of maltose-grown cells was four times greater than that of [C]glucose incorporated into the cell material of glucose-grown cells. The intracellular concentration of UTP was lower in maltose-assimilating cells than in glucose-assimilating cells. Cells grown on maltose were more spherical and less fragile than cells grown on glucose.

Journal Article↗
PubMed2000

High-affinity maltose binding and transport by the thermophilic anaerobe Thermoanaerobacter ethanolicus 39E.

Thermoanaerobacter ethanolicus is a gram-positive thermophile that produces considerable amounts of ethanol from soluble sugars and polymeric substrates, including starch. Growth on maltose, a product of starch hydrolysis, was associated with the production of a prominent membrane-associated protein that had an apparent molecular weight of 43,800 and was not detected in cells grown on xylose or glucose. Filter-binding assays revealed that cell membranes bound maltose with high affinity. Metabolic labeling of T. ethanolicus maltose-grown cells with [(14)C]palmitic acid showed that this protein was posttranslationally acylated. A maltose-binding protein was purified by using an amylose resin affinity column, and the binding constant was 270 nM. Since maltase activity was found only in the cytosol of fractionated cells and unlabeled glucose did not compete with radiolabeled maltose for uptake in whole cells, it appeared that maltose was transported intact. In whole-cell transport assays, the affinity for maltose was approximately 40 nM. Maltotriose and alpha-trehalose competitively inhibited maltose uptake in transport assays, whereas glucose, cellobiose, and a range of disaccharides had little effect. Based on these results, it appears that T. ethanolicus possesses a high-affinity, ABC type transport system that is specific for maltose, maltotriose, and alpha-trehalose.

Amino Acid Sequence↗
PubMed1995

Transient responses of Candida utilis to oxygen limitation: regulation of the Kluyver effect for maltose.

The facultatively fermentative yeast Candida utilis exhibits the Kluyver effect for maltose: this disaccharide is respired and assimilated but, in contrast to glucose, it cannot be fermented. To study the mechanism of the Kluyver effect, metabolic responses of C. utilis to a transition from aerobic, sugar-limited growth to oxygen-limited conditions were studied in chemostat cultures. Unexpectedly, the initial response of maltose-grown cultures to oxygen limitation was very similar to that of glucose-grown cultures. In both cases, alcoholic fermentation occurred after a lag phase of 1 h, during which glycerol, pyruvate and D-lactate were the main fermentation products. After ca. 10 h the behaviour of the maltose- and glucose-grown cultures diverged: ethanol disappeared from the maltose-grown cultures, whereas fermentation continued in steady-state, oxygen-limited cultures grown on glucose. The disappearance of alcoholic fermentation in oxygen-limited chemostat cultures growing on maltose was not due to a repression of the synthesis of pyruvate decarboxylase and alcohol dehydrogenase. The results demonstrate that the Kluyver effect for maltose in C. utilis does not reflect an intrinsic inability of this yeast to ferment maltose, but is caused by a regulatory phenomenon that affects a key enzyme in maltose metabolism, probably the maltose carrier. The observed kinetics indicate that this regulation occurs at the level of enzyme synthesis rather than via modification of existing enzyme activity.

Alcohol Dehydrogenase↗
PubMed1978

Pole cap formation in Escherichia coli following induction of the maltose-binding protein.

After induction with maltose, 30--40% of the total protein in the osmotic shock fluid consist of maltose-binding protein while the induction ratio (maltose versus glycerol grown cells) for the amount of binding protein synthesized as well as for maltose transport is in the order of 10. Induction of maltose transport does not occur during all times of the cell cycle, but only shortly before cell division. Electronmicroscopic analysis of cells grown logarithmically on glycerol or maltose revealed in the latter the formation of large pole caps. These pole caps arise from an enlargement of the periplasmic space. Small cells contain one pole cap, large cells contain two. Pulse label studies with strain BUG-6, a mutant that is temperature sensitive for cell division reveal the following: Growth at the non-permissive temperature prevents maltose-binding protein synthesis and formation of new transport capacity. After shifting to the permissive temperature the cells regain both functions. Simultaneously, the newly formed cells exhibit pole caps. We conclude that the induction of maltose-binding protein is responsible for the formation of pole caps. In addition, beside the presence of inducer, cell cycle events occuring during division are necessary for the synthesis of maltose-binding protein.

Biological Transport, Active↗
PubMed1976

Transport of maltose by Pseudomonas fluorescens W.

The system for uptake of maltose in Pseudomonas fluorescens W was inducible. Using a mutant strain unable to hydrolyze maltose, it was shown that maltose was taken up unaltered against a concentration gradient. Uptake of 14C maltose was only significantly inhibited by nonradioactive maltose or maltotriose. These were the only sugars that could displace accumulated radioactive maltose in the strain unable to hydrolyze maltose. Uptake exhibited saturation kinetics and was inhibited by energy poisons, indicating that this system was one of active transport. Sulfhydryl-binding reagents reversibly inhibited maltose uptake. No transport ability was lost when cells were subjected to osmotic shock. Using the protein-binding dye 7-diazonium-1, 3-naphthalene disulfonate a protein or proteins located in or external to the cell membrane was implicated in maltose transport. The hydrolysis of p-nitrophenyl-alpha-D-glucoside (PNPG) was used as an indirect measure of transport ability since penetration of PNPG, not its hydrolysis, was the rate-limiting step.

Biological Transport, Active↗
PubMed1976

[Parenteral application of maltose in diabetic patients and controls].

Maltose (10% solution) was infused continuously over 2 h (0,25 g/kg BW/h) in maturity onset diabetics (n=9) and in non-diabetic patients (n=9) serving as controls. During and after infusion changes of parameters measured (blood glucose, IRI, FFA, lactate, pyruvate, uric acid, acid-base status, ketone bodies) were minimal. A significant rise in blood-glucose was observed only in non-diabetics. Serum maltose concentrations increased continuously up to 150 mg/100 ml during infusion and were nearly identical in both groups. Post infusion serum maltose decreased slowing during 7h and urinary maltose excretion was found for 18 h. During the first 3 h controls excreted 4% of infused maltose (1.3% as maltose and 2.7% as glucose). In diabetics excretion of carbohydrates was higher and more variable: 14(1.1-35.9) %. The slight metabolic changes, especially in diabetics and the possibility of supplying more calories are favorable effects of parenteral maltose. However slow elimination and increasing urinary losses depending on dosage and conditions of i.v. maltose application account for the limited utilization of the disaccharide in men. Unless further investigations will have been done maltose cannot be recommended as a sole substitute for carbohydrate in parenteral nutrition.

Blood Glucose↗
PubMed2001

Regulation of maltose transport in Saccharomyces cerevisiae.

Solute transport in Saccharomyces cerevisiae can be regulated through mechanisms such as trans-inhibition and/or catabolite inactivation by nitrogen or carbon sources. Studies in hybrid membranes of S. cerevisiae suggested that the maltose transport system Mal61p is fully reversible and capable of catalyzing both influx and efflux transport. This conclusion has now been confirmed by studies in a S. cerevisiae strain lacking the maltase enzyme. Whole cells of this strain, wherein the orientation of the maltose transporter is fully preserved, catalyze fully reversible maltose transport. Catabolite inactivation of the maltose transporter Mal61p was studied in the presence and absence of maltose metabolism and by the use of different glucose analogues. Catabolite inactivation of Mal61p could be triggered by maltose, provided the sugar was metabolized, and the rate of inactivation correlated with the rate of maltose influx. We also show that 2-deoxyglucose, unlike 6-deoxyglucose, can trigger catabolite inactivation of the maltose transporter. This suggests a role for early glycolytic intermediates in catabolite inactivation of the Mal61 protein. However, there was no correlation between intracellular glucose-6-phosphate or ATP levels and the rate of catabolite inactivation of Mal61p. On the basis of their identification in cell extracts, we speculate that (dideoxy)-trehalose and/or (deoxy)-trehalose-6-phosphate trigger catabolite inactivation of the maltose transporter.

Adenosine Triphosphate↗
PubMed1998

Impairment by hexoses of the utilization of maltose by Saccharomyces cerevisiae.

The effect of hexoses with different transport and phosphorylation systems on the utilization of maltose by a galactose constitutive mutant of Saccharomyces cerevisiae has been studied. Galactose, mannose and fructose inhibit both the entrance of maltose in the cells and the phosphorylation of the glucose generated by intracellular hydrolysis of maltose. Transport of maltose is less affected than glucose phosphorylation and, once inside the cell, maltose is hydrolysed and the sparing glucose subsequently excreted. In addition to the well known inactivating effect of glucose, we have found that galactose inactivates the maltose transporter and that this inactivation is enhanced by maltose, which fails to inactivate the system by itself. As reported for glucose, inactivation by galactose involves proteolysis. Other strains of yeast with inducible pathways for both galactose and maltose behave similarly to the galactose constitutive mutant, with some minor changes. The use of maltose as a source of intracellular glucose has allowed to find the existence of mutual interferences in the utilization of hexoses by yeast at the phosphorylation step, that otherwise would have remained unnoticed.

Biological Transport, Active↗
PubMed1991

Inhibitions of sugar transport produced by ligands binding at opposite sides of the membrane. Evidence for simultaneous occupation of the carrier by maltose and cytochalasin B.

This study examines inhibitions of human erythrocyte D-glucose uptake at ice temperature produced by maltose and cytochalasin B. Maltose inhibits sugar uptake by binding at or close to the sugar influx site. Maltose is thus a competitive inhibitor of sugar uptake. Cytochalasin B inhibits sugar transport by binding at or close to the sugar efflux site and thus acts as a noncompetitive inhibitor of sugar uptake. When maltose is present in the uptake medium, Ki(app) for cytochalasin B inhibition of sugar uptake increases in a hyperbolic manner with increasing maltose. When cytochalasin B is present in the uptake medium, Ki(app) for maltose inhibition of sugar uptake increases in a hyperbolic manner with increasing cytochalasin B. High concentrations of cytochalasin B do not reverse the competitive inhibition of D-glucose uptake by maltose. These data demonstrate that maltose and cytochalasin B binding sites coexist within the glucose transporter. These results are inconsistent with the simple, alternating conformer carrier model in which maltose and cytochalasin B binding sites correspond to sugar influx and sugar efflux sites, respectively. The data are also incompatible with a modified alternating conformer carrier model in which the cytochalasin B binding site overlaps with but does not correspond to the sugar efflux site. We show that a glucose transport mechanism in which sugar influx and sugar efflux sites exist simultaneously is consistent with these observations.

Binding Sites↗
PubMed1984

Transport of maltose in Saccharomyces cerevisiae. Effect of pH and potassium ions.

The transport of maltose in Saccharomyces cerevisiae has been generally accepted as a H+-sugar symport, with a stoichiometrical ratio of 1:1. A simultaneous exit of K+ from the cells with the initial uptake of maltose has been reported previously. By using a K+-selective electrode and radioactive maltose, we were able to measure the exit of 1 mol of K+/mol of maltose taken up by the cells in the first 10-15 s. This stoichiometrical ratio is pH-independent. So, uptake of protons in a non-buffered cell suspension or exit of K+ in a buffered one can be used to measure initial rates of maltose uptake. We have used a K+ electrode and a pH electrode to study the effect of external pH and K+ respectively on the kinetic parameters of maltose transport. The following results were obtained: the apparent half-saturation constant for maltose (Km) increased from 5.2 mM at pH 5.8 to 38.0 mM at pH 7.8; the same increase in pH halved the apparent maximum uptake rate (Vmax); K+ had an inhibitory effect, decreasing Vmax. and increasing Km at pH values above 5; K+ had a stimulating effect at pH values below or equal to 4. Under physiological conditions, i.e. lower pH outside, neutral pH inside and much higher [K+] inside the cell, and assuming symmetry of the system, a higher affinity for maltose is to be expected in the outer face of the plasma membrane. This behaviour of the system could explain, by itself, the maintenance of the high concentration of free maltose inside the cell (necessary because of the low affinity of the maltase), without significant back transport to the outside.

Biological Transport↗
PubMed1999

The role of the trehalose system in regulating the maltose regulon of Escherichia coli.

The maltose regulon consists of 10 genes encoding an ABC transporter for maltose and maltodextrins as well as enzymes necessary for their degradation. MalK, the energy-transducing subunit of the transport system, acts phenotypically as a repressor of MalT, the transcriptional activator of the mal genes. Using MacConkey maltose indicator plates we isolated an insertion mutation that strongly reduced the repressing effect of overproduced MalK. The insertion had occurred in treR encoding the repressor of the trehalose system. The loss of TreR function led to derepression of treB encoding an enzymeIITre of the PTS for trehalose and of treC encoding TreC, the cytoplasmic trehalose-6-phosphate hydrolase. Further analysis revealed that maltose can enter the cell by facilitated diffusion through enzymeIITre, thus causing induction of the maltose system. In addition, derepression of TreC by itself caused induction of the maltose system, and a mutant lacking TreC was reduced in the uninduced level of mal gene expression indicating synthesis of endogenous inducer by TreC. Extracts containing TreC transformed [14C]-maltose into another 14C-labelled compound (preliminarily identified as maltose 1-phosphate) that is likely to be an alternative inducer of the maltose system.

ATP-Binding Cassette Transporters↗
PubMed2002

Beta-glucose 1-phosphate-interconverting enzymes in maltose- and trehalose-fermenting lactic acid bacteria.

Maltose and trehalose catabolic pathways are linked through their common enzyme, beta-phosphoglucomutase, and metabolite, beta-glucose 1-phosphate, in Lactococcus lactis. Maltose is degraded by the concerted action of maltose phosphorylase and beta-phosphoglucomutase, whereas trehalose is assimilated by a novel pathway, including the recently discovered enzyme, trehalose 6-phosphate phosphorylase, and beta-phosphoglucomutase. In the present study, 40 strains of lactic acid bacteria were investigated for utilization of metabolic reactions involving beta-glucose 1-phosphate. All genera of the low G+C content lactic acid bacteria belonging to the clostridial subbranch of Gram-positive bacteria were represented in the study. The strains, which fermented maltose or trehalose, were investigated for beta-phosphoglucomutase, maltose phosphorylase and trehalose 6-phosphate phosphorylase activity, as indications of maltose and trehalose catabolic pathways involving beta-glucose 1-phosphate interconversions. Eighty per cent of all strains fermented maltose and, of these strains, 63% were shown to use a maltose phosphorylase/beta- phosphoglucomutase pathway. One-third of the strains fermenting trehalose were found to harbour trehalose 6-phosphate phosphorylase activity, and these were also shown to possess beta-phosphoglucomutase activity. Mainly L. lactis and Enterococcus faecalis strains were found to harbour the novel trehalose 6-phosphate phosphorylase/beta-phosphoglucomutase pathway. As lower beta-glucose 1-phosphate interconverting enzyme activities were observed in the majority of glucose-cultivated lactic acid bacteria, glucose was suggested to repress the synthesis of these enzymes in most strains. Thus, metabolic reactions involving the beta-anomer of glucose 1-phosphate are frequently found in both maltose- and trehalose-utilizing lactic acid bacteria.

Culture Media↗
PubMed2006

The role of cytosolic alpha-glucan phosphorylase in maltose metabolism and the comparison of amylomaltase in Arabidopsis and Escherichia coli.

Transitory starch of leaves is broken down hydrolytically, making maltose the predominant form of carbon exported from chloroplasts at night. Maltose metabolism in the cytoplasm of Escherichia coli requires amylomaltase (MalQ) and maltodextrin phosphorylase (MalP). Possible orthologs of MalQ and MalP in the cytosol of Arabidopsis (Arabidopsis thaliana) were proposed as disproportionating enzyme (DPE2, At2g40840) and alpha-glucan phosphorylase (AtPHS2, At3g46970). In this article, we measured the activities of recombinant DPE2 and AtPHS2 proteins with various substrates; we show that maltose and a highly branched, soluble heteroglycan (SHG) are excellent substrates for DPE2 and propose that a SHG is the in vivo substrate for DPE2 and AtPHS2. In E. coli, MalQ and MalP preferentially use smaller maltodextrins (G(3)-G(7)) and we suggest that MalQ and DPE2 have similar, but nonidentical, roles in maltose metabolism. To study this, we complemented a MalQ(-) E. coli strain with DPE2 and found that the rescue was not complete. To investigate the role of AtPHS2 in maltose metabolism, we characterized a T-DNA insertion line of the AtPHS2 gene. The nighttime maltose level increased 4 times in the Atphs2-1 mutant. The comparison of maltose metabolism in Arabidopsis with that in E. coli and the comparison of the maltose level in plants lacking DPE2 or AtPHS2 indicate that an alternative route to metabolize the glucan residues in SHG exists. Other plant species also contain SHG, DPE2, and alpha-glucan phosphorylase, so this pathway for maltose metabolism may be widespread among plants.

Arabidopsis↗
PubMed2006

The importance of maltose in transitory starch breakdown.

Starch content of leaves responds to environmental stresses in various ways. Understanding these environmental effects on starch metabolism has been difficult in the past because the pathways of transitory starch synthesis and degradation are not completely known. Over the past two years there has been a significant increase in our understanding of transitory starch breakdown. The discovery of a maltose transporter (MEX1) and the studies of a cytosolic disproportionating enzyme (D-enzyme, DPE2) confirmed that maltose is the predominant form of carbon exported from chloroplasts at night. Maltose increases in leaves when starch breakdown is induced during the day under photorespiratory conditions. Maltose metabolism is regulated by a circadian clock, day length and temperature. The expression of maltose-metabolizing genes shows a pronounced circadian rhythm indicating maltose metabolism is clock regulated. Indeed, the maltose level oscillates under continuous light. The transcript of a beta-amylase gene (BAM3) peaks during the day in long days and peaks at night in short days. This could provide a mechanism for adjusting starch breakdown rates to day length. Under cold-stress conditions, maltose increases and BAM3 expression is induced. We hypothesize that maltose metabolism is a bridge between transitory starch breakdown and the plants' adaptation to changes in environmental conditions.

Chloroplasts↗