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PubMed1982

The autoradiographic utilization and distribution of [1-3H]-galactose by the dental tissues of ageing mice.

The uptake, turnover and distribution of [1-3H]-galactose by periodontal tissues associated with maxillary first molars of mice 5, 26 and 78 weeks of age showed that galactose was utilized by all oral tissues studied throughout the life-span. Uptake and turnover of the tracer revealed pulsed events. Synchrony of the pulsed events was noted. With increasing age, diminished utilization of galactose was evident, as well as a change in peak-time of the curves characteristic of ageing. The complex plots represent several metabolic events occurring simultaneously. The uptake of galactose by fibrogenic, osteogenic and cementogenic cells was low. Matrical output, on the other hand, remained high. Cementogenic cell output was the highest of all the tissues over the 30-day period. Despite decreased physiological activity with age and superimposed age changes, galactose utilization remained high throughout the study.

Aging↗
PubMed1995

A comparative study of glucose and galactose uptake in pure cultures of human oral bacteria, salivary sediment and dental plaque.

The ability to utilize glucose and the weaker sugar acidogen, galactose, was surveyed in salivary sediment, pooled dental plaque, and in pure cultures of the bacteria that numerically comprise most of the bacteria in these mixed microbial systems. Except for a veillonella isolate, which showed no uptake of either sugar, glucose was utilized more rapidly than galactose by the 27 pure cultures tested and by both sediment and plaque. This sugar difference was also seen for two other measures of glycolysis, formation of acid and previously studied ability to produce an acidic pH. Rates of uptake of the two sugars by individual pure cultures varied considerably. Generally, the Gram-positive bacteria utilized glucose and galactose at rates similar to those seen with salivary sediment and dental plaque, whereas the Gram-negative cultures tested showed much slower uptakes. Bacteria previously identified as arginolytic had lower glucose and galactose uptake rates than similar non-arginolytic micro-organisms. This, together with the ability to produce base from arginine, would explain their tendency to produce a less acidic pH. In pure culture mixtures, uptakes were generally predictable and indicated an averaging effect. When the microbial compositions of salivary sediment or dental plaque were altered by mixing with pure cultures of high glucolytic activity, such as many of the Gram-positives, glucose uptake was enhanced. The opposite was observed when the less glucolytic Gram-negative bacteria were similarly incorporated. As well as determining the glucose and galactose uptake rates of the various bacteria that collectively comprise the bulk of the salivary sediment and supragingival plaque microfloras, this study has shown how variation in microbial composition affects sugar uptake rates and has indicated how microbial composition could be manipulated to produce dental plaques with different capacities to ferment sugars and presumably different cariogenicities.

Dental Plaque↗
PubMed1984

Retinoids increase the incorporation of D-[3H]galactose into epidermal glycoproteins.

All-trans retinoic acid increased the incorporation of D-[3H]galactose into particulate and soluble glycoproteins in the epidermis of cultured pig skin slices nearly two-fold. Increased incorporation of D-[3H]galactose was not blocked by tunicamycin. This effect was specific for D-[3H]galactose since the incorporation of D-[3H]glucosamine and L-[14C]leucine into epidermal glycoproteins was unaffected by all-trans retinoic acid. All-trans retinoic acid and 13-cis retinoic acid had quantitatively similar effects on D-[3H]galactose incorporation. All-trans retinyl acetate and an aromatic retinoic acid analogue ('Etretinate') were less effective. SDS polyacrylamide gel electrophoresis and fluorography showed increased incorporation of D-[3H]galactose into all epidermal glycoproteins in the presence of all-trans retinoic acid. There was no evidence for synthesis of new glycoproteins such as mucins.

Animals↗
PubMed1988

Non-enzymic glycosylation (glycation) of lens proteins by galactose and protection by aspirin and reduced glutathione.

Radioactive galactose becomes attached covalently to lens proteins in the same way as glucose. Simultaneous incubation with aspirin inhibits the reaction with galactose in a dose-related manner. Incubation with aspirin before incubation with galactose in the absence of aspirin showed that aspirin can modify crystallins permanently to prevent the binding of galactose. The galactosylation was also inhibited by glutathione at physiological concentrations. All major groups of lens proteins reacted with galactose but a higher level of modification of protein in the material of high molecular weight may indicate that galactosylation has induced aggregation of the proteins. The modification of all major crystallin groups was confirmed by isolating the galactosylated proteins by affinity chromatography. The results are discussed in relation to glycosylation of lens proteins in diabetes and galactosaemia and the role of glycosylation in cataract.

Acetylation↗
PubMed1992

Ribose and glucose-galactose receptors. Competitors in bacterial chemotaxis.

The periplasmic ribose and glucose-galactose receptors (binding proteins) of Gram-negative bacteria compete for a common inner membrane receptor in bacterial chemotaxis, as well as being the essential primary receptors for their respective membrane transport systems. The high-resolution structures of the periplasmic receptors for ribose (from Escherichia coli) and glucose or galactose (from both Salmonella typhimurium and E. coli) are compared here to outline some features that may be important in their dual functions. The overall structure of each protein consists of two similar domains, both of which are made up of two non-contiguous segments of amino acid chain. Each domain is composed of a core of beta-sheet flanked on both sides with alpha-helices. The two domains are related to each other by an almost perfect intramolecular axis of symmetry. The ribose receptor is smaller as a result of a number of deletions in its sequence relative to the glucose-galactose receptor, mostly occurring in the loop regions; as a result, this protein is also more symmetrical. Many structural features, including some hydrophobic core interactions, a buried aspartate residue and several unusual turns, are conserved between the two proteins. The binding sites for ligand are in similar locations, and built along similar principles, although none of the specific interactions with the sugars is conserved. A comparison shows further that slightly different rotations relate the domains to each other in the three proteins, with the ribose receptor being the most closed, and the Salmonella glucose-galactose receptor the most open. The primary axis of relative rotation is almost perpendicular to that which describes the intramolecular symmetry in each case. These relative rotations of the domains are accompanied by the sliding of some helices as the structures adjust themselves to relieve strain. The hinges which are responsible for most of these relative domain rotations are very similar in the three proteins, consisting of a symmetrical arrangement of beta-strands and alpha-helices and two conserved water molecules that are critical to the hydrogen bonding in the important interdomain region. A region of high sequence and structural similarity between the ribose and glucose-galactose receptors is also located around the intramolecular symmetry axis, on the opposite side of the proteins from the hinge region. This region is that which is altered most by the relative rotations, and is the location of most of the known mutations which affect chemotaxis and transport in the ribose receptor.

Amino Acid Sequence↗
PubMed1988

Dose-dependence of endoneurial fluid sodium and chloride accumulation in galactose intoxication.

Endoneurial edema in galactose neuropathy was studied in a colony of Sprague-Dawley rats fed diets containing 0%, 10%, 20% or 40% D-galactose for approx. 200 days. Endoneurial fluid was analyzed by X-ray microanalysis for electrolyte concentration, by microgravimetry of whole nerve segments for water content, by measurement of endoneurial fluid pressure and by morphometry in transverse sections of nerve. Galactose intoxication resulted in dose-dependent increases in endoneurial fluid sodium and chloride that were directly associated with increases in nerve water content and endoneurial fluid pressure. The presence of edema and its dose-dependence was also confirmed by morphometric analysis of sciatic nerves at the light microscopic level. The data demonstrate that electrolyte-induced osmotic imbalances in endoneurial fluid are dependent on the amount of galactose ingested and suggest that the dose-related accumulation of sodium and chloride in endoneurial fluid contributes substantially to the pathogenesis of galactose neuropathy.

Animals↗
PubMed1983

Kinetics of galactose uptake by perfused rat livers: applicability of a family of models.

Mathematical models for general substrate uptake mechanisms in the liver have been used to describe the kinetics of galactose removal. In this study sets of galactose uptake rates to galactose concentration relations obtained by perfusion of ten livers of 200 g rats were examined. The rate of galactose uptake (v) was related to the galactose concentration in the sinusoids (calculated as the logarithmic mean of in- and outlet concentration, ĉ). In all experiments a saturation pattern emerged, but the resulting 1/v versus 1/ĉ plots were all markedly convex, discarding simple Michaelis-Menten kinetics. Data were therefore examined in the light of a family of kinetic models, including the following modifications: substrate inhibition, porto-systemic shunting, and allosterism. The kinetic constants were assessed by iterative procedures, aiming at linearization of the double reciprocal plots. The two latter models were found to fit the experimental data by entering a shunting of 61% of the hepatic blood flow, or two active sites, respectively. Since this degree of shunting is improbable the results speak in favour of allosterism. The work gives an example of whole-liver kinetic considerations when simple Michaelis-Menten is insufficient.

Allosteric Regulation↗
PubMed1984

Enhanced galactose metabolism in isolated perfused livers of folate-treated suckling rats.

Folic acid (1 mg/day) was administered intraperitoneally to seven-day-old suckling rats for a period of seven days. Livers of folate-treated animals took up galactose rapidly during the first 35 minutes of perfusion, whereas uptake was delayed in the controls (sham-injected and untreated). More glucose was released by all groups when galactose was perfused than when other substrates were used. With each hexose tested, livers of the folate group consistently released less glucose but more lactate than the controls. The specific activity of galactose-1-phosphate uridyltransferase was elevated in livers of the folate group compared to the controls perfused with either galactose or glucose. A similar finding was made for ATP levels in perfused livers of this group. The differences in transferase and ATP levels in perfused livers of folate-treated over the control groups may explain the enhanced galactose uptake pattern.

Adenosine Triphosphate↗
PubMed1989

Age-related changes in the galactose recognition system in rat liver cells.

In the present report, the galactose recognition system in 3- and 24-month-old rat livers has been studied with in vitro and with in situ binding experiments and in vivo ligand uptake. The galactose-specific receptors were visualized by using colloidal gold particles of different sizes (5 nm, 17 nm and 50 nm mean diameter), coated with lactosylated bovine serum albumin (LacBSA) as electron dense ligands. The data show that aging affects the expression of galactose-specific receptors and the rate of endocytosis. In the in vitro and in situ experiments hepatocytes and liver macrophages from old rats on the plasma membrane express a decreased number of binding sites with respect to those present on the adult rat liver cells. Approximately 80% of the total number of liver macrophages from aged rats show a binding distribution which is very different from the typical clustered receptor arrangement: the binding sites appear as single or small clusters of gold granules. As a direct consequence of the altered pattern of the receptor distribution, the capacity of liver macrophages from 24-month-old rats to internalize the larger ligands (17 nm and 50 nm) is decreased, as compared with adult rats. Aging, therefore, influences the galactose recognition system in two ways: (i) by decreasing the number of binding sites expressed on the liver cell surfaces; and (ii) by modifying the receptor distribution on liver macrophages and consequently affecting the internalization of galactose exposing particles.

Aging↗
PubMed1979

Isolation of galactose-inducible DNA sequences from Saccharomyces cerevisiae by differential plaque filter hybridization.

Multiple nitrocellulose DNA filter replicas of plaques of in vitro generated recombinants of phage lambda and Saccharomyces cerevisiae have been screened by hybridization with 32P-labeled cDNA probes. These probes were representative of total poly(A)-containing RNA of yeast cells grown on acetate, galactose, glucose or maltose. This approach allows the use of specific differences in total RNA populations as probes for gene isolation. Five "galactose-induced" clones have been isolated. Expression of the RNA coding regions on at least two cloned sequences, Sc481 and Sc482, is regulated by genes known to control the expression of the structural genes required for the conversion of exogenous galactose to endogenous glucose-1-phosphate. One cloned sequence, Sc484, is expressed during growth on all carbon sources except glucose, and is not under control by the galactose regulatory genes. This clone contains a sequence that is repeated 3 times in the yeast genome. The cloned fragment Sc481 contains coding regions for all or part of three galactose"induced RNAs and may correspond to the GAL 1, GAL 7, GAL 10 gene cluster region of chromosome II.

Base Sequence↗
PubMed1989

Computer modelling approach to study the modes of binding of alpha- and beta-anomers of D-galactose, D-fucose and D-glucose to L-arabinose-binding protein.

The modes of binding of alpha- and beta-anomers of D-galactose, D-fucose and D-glucose to L-arabinose-binding protein (ABP) have been studied by energy minimization using the low resolution (2.4 A) X-ray data of the protein. These studies suggest that these sugars preferentially bind in the alpha-form to ABP, unlike L-arabinose where both alpha- and beta-anomers bind almost equally. The best modes of binding of alpha- and beta-anomers of D-galactose and D-fucose differ slightly in the nature of the possible hydrogen bonds with the protein. The residues Arg 151 and Asn 232 of ABP from bidentate hydrogen bonds with both L-arabinose and D-galactose, but not with D-fucose or D-glucose. However in the case of L-arabinose, Arg 151 forms hydrogen bonds with the hydroxyl group at the C-4 atom and the ring oxygen, whereas in case of D-galactose it forms bonds with the hydroxyl groups at the C-4 and C-6 atoms of the pyranose ring. The calculated conformational energies also predict that D-galactose is a better inhibitor than D-fucose and D-glucose, in agreement with kinetic studies. The weak inhibitor D-glucose binds preferentially to one domain of ABP leading to the formation of a weaker complex. Thus these studies provide information about the most probable binding modes of these sugars and also provide a theoretical explanation for the observed differences in their binding affinities.

Arabinose↗
PubMed1977

Enzymes of galactose utilization in the rat tapeworm, Hymenolepis diminuta.

1. Crude enzyme preparations from Hymenolepis diminuta contained galactokinase, galactose 1-phosphate uridyl transferase and UDPgalactose 4-epimerase activity, although their specific activities were low. 2. Galactose 1-phosphate non-competitively inhibited galactose phosphorylation. This inhibition, together with the low specific activities of the enzymes in the pathway of galactose utilization, probably accounts for the inadequacy of galactose as a main nutritive carbohydrate for development of the worm.

Animals↗
PubMed1989

Galactose as a gratuitous inducer of GAL gene expression in yeasts growing on glucose.

The promoters of the highly expressed and stringently regulated GAL genes of Saccharomyces cerevisiae, are useful for expressing proteins in this organism. However, two problems complicate their use. First, because growth on glucose causes prolonged repression of GAL expression, cells are most rapidly induced after growth on nonfermentable carbon sources, conditions which usually support poor growth. Second, because the inducer of the GAL genes (galactose) also serves as a carbon source, the level of inducer is continually diminishing during growth of a Gal+ strain, which may lead to reduced GAL expression. To solve the first problem, we have employed strains that carry the reg1-501 mutation, which eliminates glucose repression of GAL expression. This gene has been shown to be located on the right arm of chromosome IV, distal but tightly linked to the TRP1 gene. We demonstrate that expression from GAL promoters is efficiently and rapidly induced in these reg1 strains by the addition of galactose to a culture growing in glucose medium. Levels of galactose as low as 0.02% can be used to obtain a 1500-fold induction of gene expression from GAL promoters in this strain. To surmount the second problem, we have used a gal1 mutant, deficient in the enzyme that catalyzes the first step of galactose utilization. We show that high levels of expression from GAL promoters are achieved rapidly in these mutants, for which galactose is a gratuitous inducer.(ABSTRACT TRUNCATED AT 250 WORDS)

Galactose↗
PubMed1988

Accumulation of 2-deoxy-2-[18F]fluoro-D-galactose in the liver by phosphate and uridylate trapping.

To investigate the highest accumulation of 2-deoxy-2-[18F]fluoro-D-galactose ([18F]FdGal) in the liver, metabolic studies with [18F]FdGal were carried out in Wistar rats for 120 min after i.v. injection. As main metabolites 2-deoxy-2-[18F]fluoro-D-galactose 1-phosphate ([18F]FdGal-1-P) and UDP-2-deoxy-2-[18F]-fluoro-D-galactose (UDP-[18F]FdGal) were identified in the liver and other tissues. The [18F]FdGal was phosphorylated by galactokinase. The phosphorylation rate was very rapid in the liver, in which at 5 min after injection 81% of 18F was detected as [18F]FdGal-1-P. After this time the phosphate form decreased with time, which was explained by conversion of [18F]FdGal-1-P to UDP-[18F]FdGal by UDP-glucose: galactose-1-phosphate uridyltransferase. At 120 min after injection 77% of the 18F was measured in the UDP-[18F]FdGal. In the brain both reaction rates were slower than in the liver. Both phosphate and uridylate derivates were also observed as main metabolites in the heart, lung, spleen and small intestine. On the other hand, a small amount of [18F]FdGal-1-P was detected in the plasma, in which the percentage of phosphate increased gradually and was 6% at 120 min. These results show that the [18F]FdGal metabolism in tissue results in phosphate and uridylate trapping and that the [18F]FdGal has potential for measuring in vivo galactose metabolism with positron emission tomography.

Animals↗
PubMedDate not supplied

Taurine prevents galactose-induced cataracts.

Intact lenses from New Zealand white rabbits were incubated in tissue culture media containing either 5 mM glucose or 5 mM glucose plus 30 mM galactose. The standard media did not contain taurine. Lenses were also cultured in a third medium containing 30 mM galactose plus 0.2 mM taurine. The frequency of cataract formation was evaluated as a function of the culture media. One lens (1/10), in media containing 5 mM glucose, developed a lenticular opacification during a 72-h incubation. Lenses (12/15) incubated in 30 mM galactose, without taurine, developed cataracts; fewer lenses (2/13) exposed to 30 mM galactose plus 0.2 mM taurine developed cataracts (p < 0.005). Galactose cataracts have been associated with lens edema attributed to the osmotic stress of tissue polyol (galactitol) accumulation. The water content of the noncataractous and cataractous lenses in this experiment did not differ. Lens edema, therefore, was not thought to be important in cataract pathogenesis. Taurine, an organic osmolyte was lower (5.1 +/- 1.5 mumol/g protein) in cataractous lenses than in control lenses (10.0 +/- 1.0 mumol/g protein). Malondialdehyde, an indicator of lipid peroxidation, was higher (36.6 +/- 5.0 mumol/g protein) in lens-containing opacifications than in noncataractous lenses (10.1 +/- 1.9 mumol/gm protein) (p < 0.01). The levels of malondialdehyde suggest that lipid peroxidation was increased in the process of sugar cataractogenesis. The malondialdehyde content of all the lenses correlated inversely (r = -0.53, p < 0.01) with the coincident lens taurine levels. Taurine appears to protect the lens against the development of sugar cataracts; its inverse relationship with lens malondialdehyde suggests this is an antioxidant effect.

Animals↗
PubMed2004

Involvement of PKC and PKA in the inhibitory effect of leptin on intestinal galactose absorption.

Studies from our laboratory have demonstrated that leptin inhibits galactose absorption in vitro by acting on the Na(+)/glucose cotransporter SGLT1. Since PKC and PKA are involved in the regulation of SGLT1 and leptin is able to activate these kinases, we have investigated the possible implication of PKC and PKA in the inhibition of sugar absorption by leptin in rat small intestinal rings. Inhibition of 1 mM galactose uptake by 0.2 nM leptin is blocked by 2 microM chelerythrine, a PKC inhibitor, which by itself does not affect galactose uptake. However, 1 microM H-89, a PKA inhibitor, inhibits galactose uptake and does not block leptin inhibition. Biochemical assays show that the inhibitory effect of leptin is accompanied by a approximately 2-fold increase in PKA and PKC activity. These findings indicate that the activation of PKC is more relevant than PKA activation in the inhibition of galactose absorption by leptin.

Animals↗
PubMed2005

Galactose-PEG dual conjugation of beta-(1-->3)-D-glucan schizophyllan for antisense oligonucleotides delivery to enhance the cellular uptake.

Antisense oligonucleotides (AS ODNs) are applied to silence a particular gene, and this approach is one of the potential gene therapies. However, naked oligonucleotides are easy to be degraded or absorbed in biological condition. Therefore, we need a carrier to deliver AS ODNs. This paper presents galactose moieties that were conjugated to the side chain of SPG to enhance cellular ingestion through endocytosis mediated by asialoglycoprotein receptor specifically located on parenchymal liver cells. We introduced galactose with two types of chemical bonds; amide and amine, and the amine connection showed lower ingestion and more toxicity than the amide one. Since PEG was known to induce endocytosis escape, we combined PEG and galactose aiming to provide both cellular up-take and subsequent endocytosis escape. We designed lactose or galactose moieties to attach to the end of the PEG chain that connects to the SPG side chain. When the PEG had the molecular weight of 5000-6000, the antisense effect reached the maximum. We believe that this new type of galactose and PEG dual conjugation broaden the horizon in antisense delivery.

Biocompatible Materials↗
PubMed2006

The use of single walled carbon nanotubes dispersed in a chitosan matrix for preparation of a galactose biosensor.

Chitosan was chosen as a natural polymer for dispersion of single walled carbon nanotubes (SWNT) based on its ability to efficiently solubilize SWNTs to form a stable dispersion. Moreover, chitosan films deposited on a surface of a glassy carbon (GC) electrode are mechanically stable. Further stabilisation of the chitosan film containing SWNT (CHIT-SWNT) was done by chemical crosslinking with glutaraldehyde and free aldehyde groups produced a substrate used for covalent immobilisation of galactose oxidase (GalOD). Different galactose biosensor configurations were tested with optimisation of composition of inner and outer membrane; and enzyme immobilisation procedure, as well. Detection of oxygen uptake by GalOD on CHIT-SWNT layer at -400 mV is robust and, when flow injection analysis (FIA) was applied for assays, a low detection limit (25 microM) and very high assay throughput rate (150 h-1) was achieved. This new galactose biosensor offers highly reliable detection of galactose with R.S.D. well below 2% and it has been successfully applied to assaying galactose in a blood sample with recovery index between 101.2 and 102.7%.

Biosensing Techniques↗