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PubMed1992

On the specificity of the D-galactose-binding lectin (PA-I) of Pseudomonas aeruginosa and its strong binding to hydrophobic derivatives of D-galactose and thiogalactose.

The D-galactose-binding lectin (PA-I) from the bacterium Pseudomonas aeruginosa, isolated by affinity chromatography on Sepharose, was examined for its relative affinities for simple sugars and their derivatives using equilibrium dialysis and hemagglutination inhibition tests. The lectin, which was found to bind 0.68 mol of D-galactose per subunit of 12.8 kDa, exhibited an association constant (Ka) of 3.4 x 10(4) M-1 for D-galactose and higher affinities for hydrophobic and thio derivatives of D-galactose (with highest affinity for the hydrophobic thio derivatives). alpha-Methyl-galactoside was a stronger inhibitor than the beta-methyl derivative and alpha-lactose was a weak inhibitor but the hydrophobic phenylated derivatives of the beta-configuration of D-galactose were more potent inhibitors than the respective alpha-galactosides.

Galactose↗
PubMed1976

The periplasmic galactose receptor protein of Escherichia coli in relation to galactose chemotaxis.

The periplasmic galactose receptor protein of E. coli is the common macromolecule in the initiation of two functions, chemotaxis and active transport. The substrates are glucose and galactose and the affinity for binding to the receptor protein is high (Kp -2 X 10(-8) M for glucose and 1 X 10(-7) M for galactose). A second binding site shows a 100-fold lower affinity. The high concentration of the galactose receptor protein in the periplasmic space tends to give retention through recapture of the ligands. The kinetic properties of the galactose receptor protein are, in general, in harmomy with the kinetics of chemotactic responses to spatial or temporal sugar gradients.

Biological Transport, Active↗
PubMed2001

Oxidation of galactose by galactose-1-phosphate uridyltransferase-deficient lymphoblasts.

The ability of EB virus-transformed lymphoblasts with undetectable galactose-1-phosphate uridyltransferase (GALT) from 15 galactosaemic patients to oxidize [1-(14)C]galactose to 14CO2 was compared to that of cells from 7 normal subjects. The oxidation of galactose but not of glucose was markedly diminished by cells from Q188R homozygous galactosaemic patients but was not absent. After 2.5 h these cells liberated 14CO2 at nearly 3% and at 5 h up to 9% of normal. Cells from patients homozygous for the S135L mutation produced much larger amounts of 14CO2 (15-17% of normal) and were distinguishable from the Q188R homozygous cells. A cell line with a homozygous deletion of the GALT gene oxidized galactose at 7% of the normal rate, suggesting that pathways(s) other than GALT exist in these cells as well as Q188R homozygous cells for oxidation of galactose to CO2. Concentration dependence studies are consistent with the presence of a pathway that is unsaturable or has a very high Km The ability of 10(7) lymphoblasts with the S135L genotype to oxidize more than 7% of the sugar to 14CO2 in 5 h suggests the presence of residual GALT despite the inability to detect the activity by enzymatic analysis.

Adolescent↗
PubMed2002

Galactose-1-phosphate uridyl transferase (GALT) genotype and phenotype, galactose consumption, and the risk of borderline and invasive ovarian cancer (United States).

OBJECTIVE: Previous studies have suggested that high levels of galactose consumption and/or low levels of galactose-I-phosphate uridyl transferase (GALT) activity may result in an increased risk of epithelial ovarian cancer. Similarly, some have reported that carriers of the N314D (asparagine at codon 314 replaced by aspartate) GALT polymorphism, which can be associated with low GALT activity, may have a higher risk of ovarian cancer. We examined these issues as part of a large case-control study of ovarian cancer conducted in Los Angeles between 1992 and 1998. METHODS: A total of 1,439 histologically confirmed borderline and invasive ovarian cancer cases among English-speaking non-Asian women were ascertained through the population-based cancer registry for Los Angeles County and completed in-person interviews were obtained from 689 of these (78% of cases approached). Controls consisted of 645 English-speaking non-Asian women with at least one intact ovary matched to cases on race/ethnicity (African-American, Latina, non-Latina White), date of birth (+/-3 years), and neighborhood of residence. Interviewer-administered questionnaires included information on reproductive factors, exogenous hormone use, medical history, and diet. Dietary information for the year before each case's diagnosis (and the same period for her matched control) was obtained using a self-administered food-frequency questionnaire. Blood samples were obtained from 452 controls, 136 cases with borderline ovarian cancer, and 312 cases with invasive ovarian cancer. The N314D polymorphism was characterized using PCR-RFLP and GALT enzyme activity, and was determined for a sample of the subjects with GALT genotype using an erythrocyte-based radioactive enzyme assay. RESULTS: We found no effect of N314D GALT genotype on the risk of borderline ovarian cancer (odds ratio (OR)=0.91; 95% confidence interval (CI)=0.54-1.6) or invasive ovarian cancer (OR=0.78; 95% CI= 0.53-1.2). Neither did we observe a relationship between GALT activity or lactose/galactose intake and risk of borderline or invasive ovarian cancer. Among N314D carriers, galactose consumption was associated with an increased risk of borderline (OR = 2.7, p = 0.01), but not invasive (OR = 1.2, p = 0.34), ovarian cancer; however, this result was based on only 24 N314D-positive borderline cases. CONCLUSIONS: Differences in galactose intake and GALT metabolism do not contribute significantly to the risk of ovarian cancer. There is some evidence that galactose intake may play a role in the development of borderline ovarian cancer among women who carry the uncommon GALT N314D polymorphism. More data are needed if this latter suggestion is to be definitively addressed.

Adult↗
PubMed1997

Galactose-induced dimerization of blocked ricin at acidic pH: evidence for a third galactose-binding site in ricin B-chain.

Blocked ricin is a glycoconjugate formed by covalent modification of each of the two galactose-binding sites of ricin with affinity ligands derived by modification of glycopeptides containing galactose-terminated, triantennary, N-linked oligosaccharides. Blocked ricin undergoes a pH-dependent reversible self-association, being predominantly dimeric at neutral pH and monomeric at acidic pH. The shift in the monomer-dimer equilibrium towards the monomeric form at acidic pH (pH 4) is inhibited by lactose, as shown by size-exclusion chromatography. This behavior of blocked ricin can be reproduced in studies with isolated blocked B-chain. The effect, which is dependent on the concentration of the sugar, is specific for sugars having terminal galactose moieties, or sugars having the same orientation of hydroxyl groups at C2 and C4 as galactose. These results are interpreted as providing further support for the notion that ricin B-chain has a third galactose-binding site, which may be important for the intracellular trafficking of ricin during intoxication of cells.

Binding Sites↗
PubMed1993

The MglA component of the binding protein-dependent galactose transport system of Salmonella typhimurium is a galactose-stimulated ATPase.

Binding protein-dependent transport systems mediate the accumulation of several ions, sugars, amino acids, and peptides in Gram-negative bacteria by using the energy of ATP hydrolysis and belong to a superfamily of membrane proteins which extends to eukaryotic cells and includes the multidrug resistance P-glycoprotein and the cystic fibrosis transmembrane conductance regulator. The binding protein-dependent galactose transport system of Salmonella typhimurium comprises four proteins which have been characterized previously by molecular cloning experiments (51,000-dalton MglA protein, with a stable proteolytic product of 38,000 daltons, 33,000-dalton MglB protein, 29,000-dalton MglC protein, 21,000-dalton MglE protein). By using a MglA hyperproducing strain, we have purified a galactose-stimulated ATPase which shows a single band in polyacrylamide gels under nondenaturing conditions and shows three bands at 51,000, 38,000, and 15,000 daltons on sodium dodecyl sulfate-polyacrylamide gels (our results suggest that the bands at 38,000 and 15,000 daltons represent proteolytic products of the 51,000-dalton protein). The ATPase activity coincides with the purified protein during the two last chromatographic steps of the purification procedure, and it cannot be isolated from a strain which does not contain the mglA gene. The MglA ATPase is stimulated 3-fold by galactose and hydrolyzes ATP to ADP and Pi (Km ATP = 60 microM, Ka galactose = 0.3 mM, Vmax = 140 nmol/min/mg of protein). The gamma-phosphate of ATP is transferred neither to galactose nor to the protein itself. Vanadate, N-ethylmaleimide and 5-methoxyindole-2-carboxylic acid, a specific inhibitor of binding protein-dependent transport systems, inhibit the MglA ATPase.

Adenosine Triphosphatases↗
PubMed2004

Two orthorhombic crystal structures of a galactose-specific lectin from Artocarpus hirsuta in complex with methyl-alpha-D-galactose.

Based on their carbohydrate specificity, the jacalin family of lectins can be divided into two groups: galactose-specific and mannose-specific. The former are cytoplasmic proteins, whereas the latter are localized in the storage vacuoles of cells. It has been proposed that the post-translational modification in some of the lectins that splits their polypeptide chains into two may be crucial for galactose specificity. The mannose-specific members of the family are single-chain proteins that lack the above modification. Although the galactose-specific and the mannose-specific jacalin-type lectins differ in their sequences, they share a common fold: the beta-prism I fold, which is characteristic of Moraceae plant lectins. Here, two crystal structures of a jacalin-related lectin from Artocarpus hirsuta, which is specific for galactose, in complex with methyl-alpha-D-galactose are reported. The lectin crystallized in two orthorhombic forms and one hexagonal form under similar conditions. The crystals had an unusually high solvent content. The structure was solved using the molecular-replacement method using the jacalin structure as a search model. The two orthorhombic forms were refined using data to 2.5 and 3.0 A resolution, respectively. The structures of the A. hirsuta lectin and jacalin are identical. In orthorhombic form I the crystal packing provides three different micro-environments for sugar binding in the same crystal. The observed difference in the specificity for oligosaccharides between the A. hirsuta lectin and jacalin could only be explained based on differences in the molecular associations in the packing and variation of the C-terminal length of the beta-chain. The observed insecticidal activity of A. hirsuta lectin may arise from its similar fold to domain II of the unrelated delta-endotoxin from Bacillus thuringiensis.

Amino Acid Sequence↗
PubMed1975

The transfer of galactose from UDP-galactose to endogenous lipid acceptors in liver microsomes.

When the microsomal fraction of beef liver is incubated with UDP-[14-C]-galactose in the presence of an inhibitor of nucleotide pyrophosphatase, there is an incorporation of the [14-C]galactose into glycoprotein and into two lipid components, one soluble in chloroform and the other in chloroform/methanol/water (1:1:0.3). Chromatography of the chloroform fraction on DEAE-cellulose or Kieselguhr G gives a single peak with behavior identical to that of dolichol phosphate mannose. Hydrolysis of the chloroform fraction released free galactose. It seems, therefore, that galactose, like glucose, mannose, and N-acetylglucosamine, can be transferred from its respective sugar nucleotide to glycoprotein via dolichol intermediates.

Adenosine Triphosphate↗
PubMed1981

A specific method for D-galactose quantitative determination: a modification of the D-galactose oxidase assay.

After treatment with D-galactose oxidase to form an aldehyde group, D-galactose or 2-acetamido-2-deoxy-D-galactose reacted with indole-hydrochloric acid to give a colored compound having a spectrum very similar to that of D-galacturonic acid, but with a maximum at 500 nm and a shoulder at 480 nm. The reaction is linear between 16.6 and 83 nmol of sugar per mL of final solution. 2-Amino-2-deoxy-D-galactose gave no reaction, even when 5 mumol were used, and 2-deoxy-D-lyxo-hexose did not interfere either.

Galactose↗
PubMed1999

UDP-6-deoxy-6-fluoro-alpha-D-galactose binds to two different galactosyltransferases, but neither can effectively catalyze transfer of the modified galactose to the appropriate acceptor.

The effect of substitution of the HO-6 of D-galactose with fluorine on the ability of alpha-(1-->3)-galactosyltransferase (EC 2.4.1.151) and beta-(1-->4)-galactosyltransferase (EC 2.4.1.22) to catalyze its transfer from UDP to an appropriate acceptor was determined. HPLC analyses indicated that each transferase properly catalyzed formation of the expected product [beta-D-Gal-(1-->4)-D-GlcNAc] for the beta-(1-->4)-galactosyltransferase and alpha-D-Gal-(1-->3)-beta-D-Gal-(1-->4)-D-GlcNAc for the alpha-(1-->3)-D-galactosyltransferase] when UDP-alpha-D-Gal was the substrate. When UDP-6-deoxy-6-fluoro-alpha-D-galactose (6) was used in conjunction with each transferase, no product indicative of transfer of 6-deoxy-6-fluoro-D-galactose to its respective acceptor sugar was identified. 6-Deoxy-6-fluoro-D-galactose (3) was obtained by hydrolysis of methyl 6-deoxy-6-fluoro-alpha-D-galactopyranoside, synthesized by the selective fluorination of methyl alpha-D-galactopyranoside with diethylaminosulfur trifluoride (DAST), with aqueous trifluoroacetic acid. Acetylation of 3 gave crystalline 1,2,3,4-tetra-O-acetyl-6-deoxy-6-fluoro-beta-D-galactopyranose, which was converted to the corresponding 1-alpha-phosphate and used for the synthesis of 6.

Carbohydrate Sequence↗
PubMed1999

Preventive effect of topical vitamin E-containing liposome instillation on the progression of galactose cataract. Comparison between 5-week- and 12-week-old rats fed a 25% galactose diet.

The preventive effect of topical vitamin E-containing liposome instillation on the progression of galactose cataract was compared between 5-week- and 12-week-old Wistar rats fed a 25% galactose diet. Vitamin E-containing liposomes [LP(+VE)] and vitamin E-free liposomes [LP(-VE)] were prepared with dipalmitoylphosphatidylcholine and dioleoylphosphatidylcholine (7:3 w/w). Twice daily instillation of either LP(-VE) or LP(-VE) into both eyes of 5-week-old rats fed the galactose diet for 18 days (5WGR) and 12-week-old rats fed the galactose diet for 7 weeks (12WGR) at which time some vacuoles appeared in the lens cortical equator, was conducted for a period of 4 and 9 weeks, respectively. The severity of cataracts at the end of instillation was similar in 5WGR and 12WGR. Instillation of LP(+VE), but not LP(-VE), retarded cataract progression in 5WGR and 12WGR. In 12WGR, LP(-VE) instillation caused a transient retardation of the progression. In lenses of 5WGR and 12WGR, decreases in vitamin E and reduced glutathione contents and increases in lipid peroxide, galactitol, and water contents occurred at the onset of instillation. For 5WGR, a decrease in lens reduced glutathione content and increases in lens vitamin E, lipid peroxide, galactitol, and water contents occurred at the end of instillation. For 12WGR, decreases in lens reduced glutathione and vitamin E contents and increases in lens lipid peroxide, galactitol, and water contents occurred at the end of instillation. In sera of 5WGR and 12WGR, vitamin E concentration decreased at the onset of instillation increased at the end in 5WGR and was unchanged in 12WGR. In 5WGR, instillation of LP(+VE), but not LP(-VE), for 4 weeks prevented these changes except the changes in lens galactitol and water contents and serum vitamin E concentration. In 12WGR, instillation of LP(+VE), but not LP(-VE), for 9 weeks prevented these changes except the changes in lens galactitol and water contents and serum vitamin E concentration. These results indicate that topically instilled LP(+VE) can retard cataract progression in 5WGR and 12WGR, mainly by the antioxidative action of vitamin E contained in the instilled liposomes.

Animals↗
PubMed1986

2-Deoxy-2-[18F]fluoro-D-galactose: a new tracer for the measurement of galactose metabolism in the liver by positron emission tomography.

We prepared 2-deoxy-2-[18F]fluoro-D-galactose as a potential radiopharmaceutical for liver imaging and for the assessment by positron emission tomography of regional metabolic function of the liver. In biodistribution studies of rats, the liver uptake of the compound was very high, almost reaching a plateau (6.33% dose/g) at 30 min and remaining constant until 120 min. This high uptake was reduced by simultaneous administration of D-galactose, but D-glucose had no effect. The compound was much less concentrated in the liver that had been damaged by CCl4 treatment. Positron imaging of a rabbit liver showed a remarkable uptake of the compound with a high liver-to-blood ratio. The high concentration in the liver was also reduced by the administration of D-galactose. These data suggest that the compound was trapped in the liver by a metabolic process and could be used for the measurement by positron emission tomography of galactose metabolism in the liver.

Animals↗
PubMed1984

Finding of a galactose-oxidation-product in lens of galactose-fed guinea pig.

From studies on polyols in lens of galactose-fed guinea pigs, r-galactono-1,4-lactone was found, which proves the presence of galactonic acid as a product of galactose oxidation, by gas liquid chromatography and mass spectrometry. The content of this component was one tenth of that of galactitol. In vitro culture of rat lens in 30 mM galactose-loaded media demonstrated the formation of the lactone. The significance of the lactone was discussed with respect to the galactose metabolism in lens.

Animals↗
PubMed1989

In vivo assessment of 6-deoxy-6-[18F]fluoro-D-galactose as a PET tracer for studying galactose metabolism.

The potential of 6-deoxy-6-[18F]fluoro-D-galactose (6-[18F]FdGal) as an in vivo tracer for studying galactose metabolism in tumors and liver was investigated. High uptake and rapid clearance of the radioactivity were observed in many organs of mice after i.v. injection of the tracer. D-Galactose loading did not affect liver uptake. Three experimental tumors showed a slightly higher uptake than other tissues, and rat brain tumor was clearly visualized by autoradiography. However, the radioactivity in tumors decreased rapidly. In the liver, a significant amount of the tracer was found in a galactonate form, while this oxidation was a minor metabolic pathway in the tumors. In both tumor and liver tissues, small amounts of the tracer were incorporated into macromolecular glycoconjugate via phosphate and uridylate forms as intermediate precursors. These results indicate that 6-[18F]FdGal is not suitable for studying galactose metabolism in vivo because of the low affinity of the tracer for the metabolism.

Animals↗
PubMedDate not supplied

Preparation and characterization of a bifunctional fusion enzyme composed of UDP-galactose 4-epimerase and galactose-1-P uridylyltransferase.

A fusion enzyme consisting of UDP-galactose 4-epimerase and galactose-1-P uridylyltransferase with an intervening Ala3 linker was constructed by in-frame fusion of E. coli gene galT to the 3'-terminus of the E. coli gene galE that had been extended with the coding sequence for three alanine residues, all contained within a high-expression plasmid. The fusion enzyme was expressed in E. coli and purified 24-fold to about 98% homogeneity by chromatography on hydroxylapatite and Q-Sepharose. On the basis of the comparison of the elution profile for enzyme activities upon gel permeation chromatography (Sephacryl S-400) with the molecular weight of 80,000 determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis, the fusion enzyme appears to exist in monomeric, dimeric, and tetrameric forms, all of which exhibit both enzymatic activities. The Km values of the fusion enzyme for substrates were similar to those for the corresponding native enzymes, except for UDP-glucose, but the kcat values were smaller than those for the native enzymes. The fusion enzyme shows kinetic advantages in that the initial velocity to produce glucose-1-P from UDP-galactose and galactose-1-P is about 20% faster than that for a mixture of equal activities of the separate enzymes.

Alanine↗
PubMed2006

Trypanosoma brucei UDP-galactose-4'-epimerase in ternary complex with NAD+ and the substrate analogue UDP-4-deoxy-4-fluoro-alpha-D-galactose.

The structure of the NAD-dependent oxidoreductase UDP-galactose-4'-epimerase from Trypanosoma brucei in complex with cofactor and the substrate analogue UDP-4-deoxy-4-fluoro-alpha-D-galactose has been determined using diffraction data to 2.7 A resolution. Despite the high level of sequence and structure conservation between the trypanosomatid enzyme and those from humans, yeast and bacteria, the binding of the 4-fluoro-alpha-D-galactose moiety is distinct from previously reported structures. Of particular note is the observation that when bound to the T. brucei enzyme, the galactose moiety of this fluoro-derivative is rotated approximately 180 degrees with respect to the orientation of the hexose component of UDP-glucose when in complex with the human enzyme. The architecture of the catalytic centre is designed to effectively bind different orientations of the hexose, a finding that is consistent with a mechanism that requires the sugar to maintain a degree of flexibility within the active site.

Animals↗
PubMed1982

Identification of galactose as the immunodominant sugar of leishmanial excreted factor and subsequent labeling with galactose oxidase and sodium boro[3H]hydride.

Inhibition by low-molecular-weight sugars of precipitin line formation between a polysaccharide (EF) excreted by Leishmania tropica subsp. major, Leishmania enriettii, and rabbit antileishmanial antibodies on double gel diffusion plates revealed that galactose residues, possibly as components of lactosyl groups, were the critical immunodominant sugars mediating antibody recognition of EF. The galactose residues of the EF of L. tropica subsp. major were specifically labeled with tritium via galactose oxidase and sodium boro[3H]hydride. The radioactive EF had an apparent molecular weight of about 85,000 on sodium dodecyl sulfate-polyacrylamide gels and was precipitated by antileishmanial antibodies as well as Ricinus communis lectins I and II (galactose specific). Lectins specific for glucose-mannose residues, fucose, N-acetylglucosamine, and N-acetylgalactosamine did not precipitate the labeled EF. Treatment of [3H]EF with proteolytic (trypsin, papain, protease) or glycosidic (alpha-amylase, beta-galactosidase) enzymes had no effect on either the electrophoretic pattern of the material or on its recognition by antileishmanial antibodies or R. communis lectin. This resistance to enzyme activity suggests that EF may be a useful marker for the presence of the parasite in vivo if it can be detected in minute quantities.

Animals↗
PubMed1968

Galactose transport in Saccharomyces cerevisiae. I. Nonmetabolized sugars as substrates and inducers of the galactose transport system.

The inducible galactose transport system in bakers' yeast carries out the facilitated diffusion of the nonmetabolized galactose analogues d-fucose and l-arabinose. This capacity depends on the activity of the Ga 2 gene. In some strains, d-fucose and l-arabinose are also gratuitous inducers. Mutants in which the inducibility of the galactose pathway enzymes is altered show a parallel alteration of the inducibility of the galactose transport system.

Arabinose↗