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PubMed2003

Establishment of the mimetic aging effect in mice caused by D-galactose.

We successfully established an oxidant damage of mimetic aging model using mice induced by D-galactose, and the mimetic aging model is relative to free radical and the accumulation of waste substances in metabolism. The animals were divided into 3 groups: (1) phosphate-buffered saline (PBS); (2) 1% D-galactose; (3) 5% D-galactose by subcutaneous injection every day. After 45 days, mice treated with D-galactose showed a significant increase in the malondialdehyde (MDA), total antioxidant status (TAS) and a decrease in superoxide dismutase (SOD) in the blood compared with the PBS group. In the brain, the D-galactose treated mice exhibited a higher level MDA and a lower level SOD activity. In the liver, only the 5% D-galactose group indicated a significant increase in MDA. By reference to the oxidative biomarkers in blood, brain and liver, we have confirmed the reliability of the mimetic aging model.

Aging↗

PubMed1978

The metabolic response to galactose as a measure of hepatic glucose release in man.

1. Galactose utilization after intravenous injection was measured in fed and fasted man together with changes in blood glucose, lactate and insulin. 2. Feeding did not alter blood galactose half-life. 3. The mean increases in blood glucose and lactate were greater in the fasted subjects but their concentrations reached similar values in both fed and fasted states. 4. Plasma insulin increased after galactose in the fasted state, but there was no change in the fed state, indicating that galactose is not insulinogenic. 5. After an intravenous galactose load in the fed state insulin appears to inhibit hepatic glucose release. 6. An intravenous galactose test might be a useful measure of hepatic glucose release under different physiological and pathological conditions.

Adult↗

PubMed2003

UDP-galactose 4-epimerase: a key enzyme in exopolysaccharide formation by Lactobacillus casei CRL 87 in controlled pH batch cultures.

AIMS: To evaluate the relationship between exopolysaccharide (EPS) production and the sugar nucleotide biosynthetic enzymes in Lactobacillus casei CRL 87 under optimum growth conditions for polymer formation: controlled pH on galactose or glucose. Studies with an EPS mutant were carried out to determine the key enzymes in EPS synthesis under the above culture conditions. METHODS AND RESULTS: EPS concentration was estimated by the phenol/sulphuric acid method, while the activities of the biosynthetic enzymes were determined spectrophotometrically by measuring the formation or disappearance of NAD(P)H at 340 nm. An environmental pH of 5.0, using galactose as carbon source, markedly improved not only polymer production and yield but also, cell growth and lactic acid production. Analysis of the activities of the EPS precursor-forming enzymes revealed that polysaccharide synthesis was correlated with uridine-diphosphate (UDP)-glucose pyrophosphorylase and UDP-galactose 4-epimerase under these growth conditions. CONCLUSIONS: EPS synthesis by Lact. casei CRL 87 was considerably improved at a controlled pH of 5.0 with galactose as carbon source, and was correlated with the activity of UDP-glucose pyrophosphorylase and UDP-galactose 4-epimerase. The results obtained with the wild-type and EPS- strains suggest that UDP-galactose 4-epimerase plays an essential role in EPS formation. SIGNIFICANCE AND IMPACT OF THE STUDY: Unravelling the key enzymes involved in EPS biosynthesis under optimum culture conditions for polymer production provides important information for the design of strategies, via genetic engineering, to enhance polysaccharide formation.

Culture Media↗

PubMed1973

Population analysis of the deinduction kinetics of galactose long-term adaptation mutants of yeast.

By use of a selective galactose agar medium containing ethidium bromide, a population analysis of the deinduction kinetics of yeast galactose long-term adaptation mutants (gal 3) has been done. It was first determined that the gal 3 mutation is specific to the yeast galactose system and that induced cultures of gal 3 strains are capable of growth on galactose agar medium containing ethidium bromide, whereas noninduced cultures are not. Population analyses of induced gal 3 strains under going deinduction in the absence of galactose demonstrate that a minimum number of five induction units per cell are required for induction of the galactose system. It is concluded that: these induction units are actively synthesized only in the presence of inducer and are diluted out through cell division; they are stable under nongrowing conditions; they are heterogeneous in nature; at most two of the five minimum units are products of the gal 2 locus; and the other units may be three of one type, one of one type and two of another, or one each of three different types.

Enzyme Induction↗

PubMed1978

Myoinositol and phosphatidylinositol metabolism in synaptosomes from galactose-fed rats.

The effects of experimental galactose toxicity on inositol and phosphatidylinositol (PtdIns) metabolism in synaptosomes from 0- to 30-day-old rats were investigated. Galactose toxicity was induced by feeding mothers a 40% galactose diet from the 12th day of pregnancy until 19 days postpartum when the offspring were weaned onto the maternal diet. There was no decrease in myoinositol concentrations and only a small decrease in PtdIns in synaptosomes from galactose-fed rats relative to glucose-fed controls. Synaptosomes from rats on the two diets converted equivalent amounts of [U-14C]glucose to inositol and PtdIns. Acetylcholine stimulated [2-3H]inositol incorporation into PtdIns while producing a net decrease in PtdIns concentration in synaptosomes from 22- to 30-day-old rats. However, the phospholipid response to acetylcholine in synaptosomes from galactose-fed rats was impaired. Thus, the acetylcholine-stimulated labeling of PtdIns was 40--50% lower in these synaptosomes while the effect on PtdIns concentration was reduced by a maximum of 55%. The data suggest that galactose-fed rats may have either a deficiency in the number of acetylcholine receptors or a defect in some step between receptor-neurotransmitter interaction and PtdIns breakdown.

Acetylcholine↗

PubMed1995

The role of tryptophans 371 and 395 in the binding of antibiotics and the transport of sugars by the D-galactose-H+ symport protein (GalP) from Escherichia coli.

The interactions between the D-galactose-H+ symporter (GalP) from Escherichia coli and the inhibitory antibiotics, cytochalasin B and forskolin, and the substrates, D-galactose and H+, have been investigated for the wild-type protein and the mutants Trp-371-->Phe and Trp-395-->Phe, so that the roles of these residues in the structure-activity relationship could be assessed. Neither mutation prevented photolabeling by either [4-3H]cytochalasin B or by 3-[125I]iodo-4-azidophenethyl-amido-7-O-succinyldesacetylforskolin ([125I]APS-forskolin). However, measurements of protein fluorescence show that both residues are in structural domains, the conformations of which are perturbed by the binding of cytochalasin B or forskolin. Moreover, both mutations cause a substantial decrease in the affinity of the inward-facing site of the GalP protein for cytochalasin B, 10- and 43-fold, respectively, but have little effect upon the affinity of this site for forskolin, 0.8- and 2.6-fold reductions, respectively. Both these mutations change the equilibrium between the putative outward- (T1) and inward-facing (T2) conformations, so that the inward-facing form is more favored. They also stabilize a different conformational state, "T3-antibiotic," in which the initial interactions between the protein and antibiotics are tightened. Overall, this has the effect of compensating for the reduction in affinity for cytochalasin B, so that the respective overall Kd values are 0.74- and 3.5-fold that of the wild type, while causing a slight increase, 1.5- and 3.2-fold, respectively, in affinity of the mutants for forskolin. The Trp-371-->Phe mutation causes a 15-fold reduction in the affinity of the inward-facing site for D-galactose, suggesting that this residue forms part of the sugar binding site. In contrast, the Trp-395-->Phe mutation has no effect upon the affinity of the inward-facing site for D-galactose. These effects may be related to the reduction in galactose-H+ symport activity only in the Trp-371-->Phe mutant, although it still effects active transport to the same extent as the Trp395-->Phe mutant. However, there is a 10-20-fold increase in the Km values for energized transport of D-galactose for both mutants.

Anti-Bacterial Agents↗

PubMed2000

Three aromatic amino acid residues critical for galactose transport in yeast Gal2 transporter.

Tyr(446) in putative transmembrane segment 10 (TM10) of the yeast galactose transporter Gal2 has previously been identified as essential for galactose recognition. In the present study, alignment of the amino acid sequences of 63 sugar transporters or related proteins revealed 14 aromatic sites, including Tyr(446) of Gal2, that are conserved in >75% of these proteins. The importance of the remaining 13 conserved aromatic amino acids was examined individually by random mutagenesis using degenerate primers. Galactose transport-positive clones were identified by plate selection and subjected to DNA sequencing. For those transport-positive clones corresponding to Tyr(352), and Phe(504) mutants, all the amino acid substitutions comprised aromatic residues. The importance of the aromatic residues at these sites was further investigated by replacing them individually with each of the other 19 amino acids and measuring the galactose transport activity of the resulting mutants. Among both Tyr(352) and Phe(504) mutants, the other aromatic amino acids supported galactose transport; no other amino acids conferred high affinity transport activity. Thus, at least three aromatic sites are critical for galactose transport: one at the extracellular boundary of putative TM7 (Tyr(352)), one in the middle of putative TM10 (Tyr(446)), and one in the middle of putative TM12 (Phe(504)).

Amino Acids↗

PubMed2006

The regulatory roles of the galactose permease and kinase in the induction response of the GAL network in Saccharomyces cerevisiae.

The GAL genetic switch of Saccharomyces cerevisiae exhibits an ultrasensitive response to the inducer galactose as well as the "all-or-none" behavior characteristic of many eukaryotic regulatory networks. We have constructed a strain that allows intermediate levels of gene expression from a tunable GAL1 promoter at both the population and the single cell level by altering the regulation of the galactose permease Gal2p. Similar modifications to other feedback loops regulating the Gal80p repressor and the Gal3p signaling protein did not result in similarly tuned responses, indicating that the level of inducer transport is unique in its ability to control the switch response of the network. In addition, removal of the Gal1p galactokinase from the network resulted in a regimed response due to the dual role of this enzyme in galactose catabolism and transport. These two activities have competing effects on the response of the network to galactose such that the transport effects of Gal1p are dominant at low galactose concentrations, whereas its catabolic effects are dominant at high galactose concentrations. In addition, flow cytometry analysis revealed the unexpected phenomenon of multiple populations in the gal1delta strains, which were not present in the isogenic GAL1 background. This result indicates that Gal1p may play a previously undescribed role in the stability of the GAL network response.

Galactokinase↗

PubMed1997

Effects of aldose reductase inhibitor CT-112 on the corneal epithelial barrier of galactose-fed rats.

PURPOSE: To investigate whether the barrier function of the corneal epithelium is disrupted in galactosemic rats, and to assess the effects of the aldose reductase inhibitor CT-112, in the form of eyedrops, on the corneal epithelial barrier in galactosemic rats. METHODS: Forty rats were divided into 3 groups based on their diet: a control group, a galactose group and a CT-112 treated galactose group (CT-112 group). After 3 weeks, 31 rats from the 3 groups were subjected to fluorophotometry, in which fluorescein (F) was instilled into one eye and carboxyfluorescein (CF) was instilled into the other eye in a random fashion. The F and CF uptakes were then measured at the central cornea by a slit-lamp fluorophotometer. Three rats from each group were exposed to a horseradish peroxidase (HRP) solution for one hour, and the HRP-reactive substances within the corneal epithelium were also examined via electron microscopy. RESULTS: There was significantly higher F uptake in the galactose group than in the control (p = 0.003) and CT-112 groups (p = 0.028). There were no significant differences in CF uptake between the 3 groups. Histologically, HRP-reactive substances were found in much greater quantities within the superficial corneal cells of the galactose group than in the control or CT-112 groups. CONCLUSIONS: These results suggest that cell membrane disruption, as detected by F uptake and HRP penetration, was found in the superficial corneal cells of galactose-fed rats, and that intercellular junction integrity can be assayed by CF uptake and histological evaluation. Moreover, CT-112 eyedrops were effective in improving the corneal epithelial barrier dysfunction of galactose-fed rats.

Aldehyde Reductase↗

PubMed1966

Radioautographic comparison of the uptake of galactose-H and glucose-H3 in the golgi region of various cells secreting glycoproteins or mucopolysaccharides.

The radioautographic distribution of the label of galactose-H(3) was compared with that of glucose-H(3) in a series of secretory cells of the rat. Whereas the glucose label appeared in all mucous cells, the galactose label was incorporated only into certain mucous cells. Whenever either label was incorporated, however, it was located first in the Golgi region and later in the secretion product, mucus. Several lines of evidence, including extraction of glucose label with peracetic acid-beta glucuronidase, indicated that the material synthesized in the Golgi region was glycoprotein in nature. In chondrocytes, both the galactose and the glucose label appeared first in the Golgi region and later in cartilage matrix; extraction of glucose label with hyaluronidase indicated that much of it consisted of mucopolysaccharide. In all secretory cells, the extraction of glycogen by amylase had no effect on Golgi radioactivity. Such extraction did not eliminate the scattered cytoplasmic label also seen after glucose-H(3) injection, but completely eliminated that seen after galactose-H(3). Consequently, the galactose-H(3) label in the Golgi region stood out more clearly, and was detected in many cells: pancreas, liver, epididymis, and intestinal columnar cells. In the latter, label later appeared in the surface coat. Thus, radioautography after injection of galactose-H(3), as after glucose-H(3), indicates that synthesis of complex carbohydrates takes place in the Golgi region of many secretory cells.

Amylases↗

PubMed1992

Effect of aldose reductase inhibitors on lenticular dulcitol level in galactose fed rats.

We have shown that galactose cataract development is delayed or inhibited with the administration of aldose reductase inhibitors (ARIs). Dulcitol forms and accumulates in the lens of rats fed galactose. We undertook investigations to study the effectiveness of ARIs in preventing the formation and accumulation of dulcitol in the lens. Young Sprague Dawley rats were fed Purina Rat Chow with 50% galactose either with or without 15 mg sorbinil, 0.15, 0.5, or 1.0 mg E-0722/day/Kg body weight. At desired intervals following the initiation of diets, the lenses were processed for the determination of galactose and dulcitol levels. The lenticular dulcitol increased significantly in all animals fed galactose reaching a maximum level by approximately 15 days with comparatively lower levels in the groups fed ARIs with galactose; this increase was dose dependent in the groups fed E-0722. There was a subsequent, rapid drop in lenticular dulcitol by 18 days in all dietary groups. Interestingly, a second peak of increased lenticular dulcitol was observed in all groups. The correlation between dulcitol accumulation and cataract development is discussed.

Aldehyde Reductase↗

PubMed1995

Permeability of the blood-retinal and blood-aqueous barriers in galactose-fed rats.

Blood-retinal barrier (BRB) and blood-aqueous barrier (BAB) permeability were assessed by various methods to clarify conflicting reports on whether blood-retinal barrier permeability changes occur in diabetic and galactose-fed rats and to assess the potential role of aldose reductase in this process. Different molecular weight probes were utilized in rats fed for 7-11 months either a normal diet or a diet containing 50% galactose with/without the aldose reductase inhibitor AI1576 or Ponalrestat. BRB and BAB were assessed through radiolabelled sucrose permeability studies in eyes where the anterior segment was frozen during dissection compared to eyes where the anterior segments were not frozen and by quantitative autoradiography. In addition, histological studies using Evans Blue dye, microperoxidase and horseradish peroxidase were conducted. In untreated galactose-fed rats a 4-fold increase in the mean permeability surface area product (PA) to sucrose at the BRB was observed when the aqueous humor was not frozen during retinal dissection. However, no increase in the mean PA to sucrose was observed when the aqueous humor of similar eyes was frozen during dissection. Similarly, no retinal vessel permeability increase was observed by either quantitative autoradiography of [3H]-sucrose after 15 minutes of circulation or histological studies with microperoxidase, horseradish peroxidase or Evans Blue dye. Examination of the BAB revealed an increase in the permeability of iris vessels but not the ciliary body in galactose-fed rats which was reduced by treatment with the aldose reductase inhibitor AI1576. These data indicate that while BRB permeability is not increased in galactose-fed rats, BRB permeability measurements with isotopes are subject to possible contamination from the aqueous humor in untreated galactose-fed rats, which can result in false observations of increased BRB permeability.

Aldehyde Reductase↗

PubMed1999

Inhibition of galactose-induced cataractogenesis by troglitazone, a new antidiabetic drug with an antioxidant property, in rat lens culture.

Troglitazone is a new antidiabetic drug with a combined chemical structure of thiazolidinedione and alpha-tocopherol like structure (chroman ring). We evaluated the effect oftroglitazone on the morphological and biochemical changes in rat lenses cultured with galactose. Culturing in 30 mM galactose medium for 48 hrs resulted in vacuole formation in the cortex of lens equator (early phase of cataract). A significant amount of galactitol accumulation and lipid peroxide formation were also observed in lenses exposed to galactose. These morphological and biochemical changes associated with galactose were inhibited by 2 or 20 microM troglitazone present in the galactose medium. These results confirm the previous finding that troglitazone delayed the formation of cataract in rats fed a galactose diet. The anticataract effect of troglitazone was discussed in terms of antioxidant property of the drug.

Aldehyde Reductase↗

PubMed2000

Preventive effect of vitamin E-containing liposome instillation on cataract progression in 12-month-old rats fed a 25% galactose diet.

The preventive effect of vitamin E (Vit. E)-containing liposome instillation on cataract progression was examined in 12-month-old Wistar rats fed a 25% galactose diet. Vit. E-containing liposomes prepared with dipalmitoylphosphatidylcholine and dioleoylphosphatidylcholine (7:3 w/w) were instilled into both eyes twice a day. Lenses of galactose-fed rats showed suture accentuation at 6 months of feeding and opacities in the cortex and nuclei at 8 months. Two months of Vit. E-containing liposome instillation, starting at 6 months of galactose feeding, retarded this cataract progression. Lenses of galactose-fed rats had increased Vit. E, lipid peroxide (LPO), galactitol, and water contents and decreased reduced glutathione (GSH) content at 6 months of feeding; increased LPO, galactitol, and water contents and decreased GSH content at 8 months. Sera of galactose-fed rats had increased Vit. E and cholesterol concentrations at 6 months of feeding. The liposome instillation increased lens Vit. E content with attenuation of the increased lens LPO content and the decreased lens GSH content but did not affect the changes in lens galactitol and water contents and serum Vit. E and cholesterol concentrations. These results indicate that instilled Vit. E-containing liposomes retard cataract progression in 12-month-old rats fed a 25% galactose diet, mainly by the antioxidative and membrane-stabilizing actions of Vit. E contained in the liposomes.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2006

Incorporation of orally applied (13)C-galactose into milk lactose and oligosaccharides.

Biosynthesis and functions of human milk oligosaccharides (HMO) are not well known. A typical housekeeping enzyme, beta1,4-galactosyltransferase, links galactose to glucose to form lactose which is then used as backbone for the assembly of HMO. We investigated whether milk lactose and HMO may be labeled in vivo by an orally given (13)C-galactose bolus. Eleven exclusively breastfeeding mothers were given a (13)C-galactose bolus at the end of their breakfast. Milk and urine samples from each nursing up to 36 h were analyzed for carbohydrate composition by high-performance thin-layer chromatography, high-pH anion-exchange chromatography, and fast atom bombardment mass spectrometry. (13)C enrichment of milk fractions, urinary carbohydrates, lactose, and oligosaccharides as well as of breath CO(2) was determined by isotope ratio mass spectrometry. Up to 10% of the orally given galactose bolus was directly transported to the mammary gland and incorporated into milk components. Characteristic for most milk samples was the appearance of two (13)C-peaks, the first immediately after the (13)C-bolus was taken and the second on the next morning. The highest (13)C enrichment was found in lactose followed by neutral and acidic oligosaccharides. In breath samples, the (13)C-excretion followed the same pattern as in milk. (13)C nuclear magnetic resonance of isolated lactose revealed (13)C only at C(1)-atom of galactose and C(1)-atom of glucose. This label was without any exception at the same position as the (13)C-label of the orally applied galactose. Neutral and acidic HMO can easily be (13)C-labeled in vivo which facilitates investigations of their metabolic fate in infants.

Administration, Oral↗

PubMed1990

Galactose removal kinetics during hypoxia in perfused pig liver: reduction of Vmax, but not of intrinsic clearance Vmax/Km.

The galactose elimination kinetics was examined in five perfused pig livers of 1.2 kg during hypoxia induced by administration of 2, 4 or 7% oxygen in the oxygenator instead of 20% as used in nine control experiments, previously published. Galactose was given as four to five successive constant infusion rates so that successive steady-state period with galactose concentrations from 0.04 to 5 mmol l-1 were obtained in each experiment. From the relationship between the calculated elimination rate and the perfusate galactose concentration, values of the maximal elimination rate Vmax and the half saturation concentration Km were calculated. Both Vmax and Km were reduced by hypoxia: the lower the oxygen supply, the greater the reduction. Vmax was about 0.08 mmol min-1 kg-1 liver at 2% oxygen and about 0.18 mmol min-1 kg-1 liver at 4-7% oxygen; both being significantly lower than the value of 0.43 mmol min-1 kg-1 liver at 20% oxygen. Km was about 0.07 mmol l-1 at 2% oxygen and 0.13 mmol l-1 at 7% oxygen; both significantly lower than the value of 0.23 mmol l-1 at 20% oxygen. A nearly parallel reduction of liver ATP concentration and galactose Vmax indicates that the galactose Vmax may reflect the phosphorylation capacity of the liver cells. The Vmax/Km ratio (intrinsic hepatic clearance) was unchanged during hypoxia.

Animals↗

PubMed2006

Sequence, organization, transcription and regulation of lactose and galactose operons in Lactobacillus rhamnosus TCELL-1.

AIMS: Understanding the metabolism of lactose and galactose and their regulation in Lactobacillus rhamnosus. METHODS AND RESULTS: A gene cluster containing nine open reading frames (ORFs) involved in the metabolism of lactose and galactose in Lact. rhamnosus TCELL-1 was sequenced and characterized. The order of the ORFs was lacTEGF and galKETRM. Northern blotting experiments revealed that the gene cluster could be transcribed as one lacTEGF-galKETRM mRNA though three major transcripts (lacTEGF, galKETRM and galETRM) were detected for the gene cluster. The transcription of the lac or gal operon was independently induced in the presence of lactose or galactose. Northern blotting and primer extension experiments found the presence of four putative promoters upstream from the ORFs lacT (lacTp), galK (galKp1 and galKp2) and galE (galEp). The measurements of enzymatic activities of GalK, GalE and GalT suggested that the expression of the gal operon was subjected to a galactose activation and glucose repression mechanism. CONCLUSIONS: In Lact. rhamnosus TCELL-1, the galactose moiety of lactose could be metabolized by two alternative pathways (the Leloir and the tagatose 6-phosphate pathways) whereas galactose metabolism could be mediated by the Leloir pathway. SIGNIFICANCE AND IMPACT OF THE STUDY: This work provides important information about sugar metabolism in Lact. rhamnosus.

Amino Acid Sequence↗

PubMed1992

Isolation and characterization of acetic acid-tolerant galactose-fermenting strains of Saccharomyces cerevisiae from a spent sulfite liquor fermentation plant.

From a continuous spent sulfite liquor fermentation plant, two species of yeast were isolated, Saccharomyces cerevisiae and Pichia membranaefaciens. One of the isolates of S. cerevisiae, no. 3, was heavily flocculating and produced a higher ethanol yield from spent sulfite liquor than did commercial baker's yeast. The greatest difference between isolate 3 and baker's yeast was that of galactose fermentation, even when galactose utilization was induced, i.e., when they were grown in the presence of galactose, prior to fermentation. Without acetic acid present, both baker's yeast and isolate 3 fermented glucose and galactose sequentially. Galactose fermentation with baker's yeast was strongly inhibited by acetic acid at pH values below 6. Isolate 3 fermented galactose, glucose, and mannose without catabolite repression in the presence of acetic acid, even at pH 4.5. The xylose reductase (EC 1.1.1.21) and xylitol dehydrogenase (EC 1.1.1.9) activities were determined in some of the isolates as well as in two strains of S. cerevisiae (ATCC 24860 and baker's yeast) and Pichia stipitis CBS 6054. The S. cerevisiae strains manifested xylose reductase activity that was 2 orders of magnitude less than the corresponding P. stipitis value of 890 nmol/min/mg of protein. The xylose dehydrogenase activity was 1 order of magnitude less than the corresponding activity of P. stipitis (330 nmol/min/mg of protein).

Acetates↗