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PubMed1975

Galactose-specific messenger ribonucleic acid contents in Escherichia coli: effect of inducer, gene dosage and galactose genotype.

Galactose specific mRNA (gal-mRNA) and galactokinase were measured in strains of E.coli with varying numbers of copies of the galactose operon. While the fucose induction the amount of gal mRNA has been found to be proportional to the content of galactokinase and to the gene frequency, with galactose induction this was not the case. It is suggested that this is a result of the metabolism of galactose leading to catabolite repression. The amounts of gal-mRNA and galactokinase were also measured in a series of polar mutants. With increasing polarity, there was a greater effect on enzyme content than on gal-mRNA. This suggests that the effect of polarity on RNA is the result of degradation after synthesis rather than prevention of transcription. A method of correlating hybridisation data with the genetic map is described.

Bacteriological Techniques↗
PubMed1980

[The galactose breath test. Modification of the method and comparison with galactose elimination capacity and plasma disappearance of bromsulphatein (author's transl)].

The paper describes a modification of the galactose breath test (GBT) for assessing liver function. Following iv injection of 0.5 g galactose per kg body weight, together with 2 mu Ci generally 14C-labelled galactose, 14CO2 is collected in regular intervals during one hour. Since 14C-activity in breath exhibits a linear rise during 70--100 minutes, the curve obtained permits calculation of an initial slope, as well as the "standardized specific activity" after 45 min GBT was performed in 8 liver normals, 8 alcoholic cirrhotics, 4 patients with chronic active hepatitis (CAH) and 6 with primary biliary cirrhosis (PBC). The results were compared with the simultaneously measured galactose elimination capacity (GEC) and the initial plasma disappearance (ki) of bromsulphthalein (BSP). In the liver normals, the values for initial slope and standardized specific activity were 1.08 +/- S.D. 0.3 and 0.42 +/- S.D. 0.1, respectively. In comparison, the values obtained in all patients groups were markedly reduced. CAH patients exhibited the most severe decrease; the reduction was smallest in PBC patients. The GBT discriminated well between liver normals and patients with liver disease (p less than 0.001, t-test). The results of the GBT correlated linearly with GEC (r = 0.86 and 0.87, respectively) and with BSP-ki (r = 0.9 and 0.92, respectively). These results suggest that the GBT may be regarded as a quantitative measure of a cystosolic hepatic function.

Aged↗
PubMed1982

Glycoprotein Biosynthesis in Chlamydomonas: I. IN VITRO INCORPORATION OF GALACTOSE FROM UDP-[C]GALACTOSE INTO MEMBRANE-BOUND PROTEIN.

A crude membrane fraction from Chlamydomonas reinhardii was found to catalyze d-galactose transfer from UDP-galactose to endogenous proteins. Highest incorporation rates were achieved by incubation at 25 degrees C and pH 7.5 in the presence of 10 millimolar Fe(2+). Hydrolytic studies on the labeled polymer revealed that radioactivity was attached to protein via an alkali-stable and acid-labile linkage. Identification of galactose as the only labeled sugar in the acid hydrolysate and results of a tentative estimation of the molecular weight of the charged alkaline degradation product indicate that monomeric galactose units are transferred to form an O-glycosidic bond with peptidyl hydroxyproline. No indications were found for a similar linkage to serine which, in contrast to the hydroxyproline-O-glycoside linkage, is acid-stable but is cleaved by beta-elimination. Chromatography of the sodium dodecyl sulfate-solubilized polymer on Sepharose-6B demonstrated that galactosyl residues are mainly associated with proteins which are of considerably higher molecular weight than are the majority of sodium dodecyl sulfate-denatured membrane proteins in this fraction.

Journal Article↗
PubMed1976

Galactose transfer and UDP-galactose hydrolysis in urine from normal Balb/c and Balb/c YC8 mice.

By chromatographic method we have shown the existence of a complex system for galactose transfer from UDP-galactose and for nucleotide hydrolysis in urines from Balb/c YC8 and normal Balb/c mice. By action of sera from normal and ascitic mice as source of enzyme, we have been able to detect transfer for galactose in urines from ascitic mice and an important inhibitory effect of the nucleotide sugar hydrolysis by the sera with urines from normal mice.

Animals↗
PubMed1992

Colorimetric determination of galactose and galactose-1-phosphate from dried blood.

A colorimetric microassay for the simultaneous quantitative determination of galactose (Gal) and galactose-1-phosphate (Gal-1-P) in dried blood spots is described. An enzymatic reaction involving alkaline phosphatase (EC 3.1.3.1) and galactose dehydrogenase (EC 1.1.1.48) produces NADH, which is coupled with diaphorase (EC 1.8.1.4) and iodonitrotetrazolium violet (INT). The colourless INT is converted to a formazan of red colour the intensity of which is quantitated either photometrically by a microplate reader or determined visually with sufficient sensitivity for screening purposes. We evaluated the assay on 200,000 blood samples in a newborn screening program, and were able to distinguish between classical and milder forms of galactosemia with ease.

Alkaline Phosphatase↗
PubMed1989

2-Deoxy-2-[18F]fluoro-D-galactose as an in vivo tracer for imaging galactose metabolism in tumors with positron emission tomography.

The feasibility of 2-deoxy-2-[18F]fluoro-D-galactose ([ 18F]FdGal) for imaging galactose metabolism in tumors with positron emission tomography (PET), was investigated using two hepatomas, Yoshida sarcoma, or glioma in rats, and mouse mammary carcinoma. In hepatoma-bearing rats the highest uptake of [18F]FdGal was observed in the liver followed by the kidney and tumor. The tumor uptake increased with time, and the high uptake ratios of tumor to organ were observed except for the liver and kidney. Tumor uptake was also measured in all tumors. As main metabolites in all tumors, [18F]FdGal 1-phosphate and UDP-[18F]FdGal were found by HPLC. Two hepatomas showed a slightly higher uptake and a larger percentage of UDP derivative than the other three tumors. By autoradiography the brain tumor was visualized clearly. These results indicate that [18F]FdGal has potential as a tracer for imaging galactose metabolism in tumors with PET.

Animals↗
PubMed2002

Galactose biosynthesis in Arabidopsis: genetic evidence for substrate channeling from UDP-D-galactose into cell wall polymers.

The biosynthesis of plant cell wall polysaccharides requires the concerted action of nucleotide sugar interconversion enzymes, nucleotide sugar transporters, and glycosyl transferases. How cell wall synthesis in planta is regulated, however, remains unclear. The root epidermal bulger 1 (reb1) mutant in Arabidopsis thaliana is partially deficient in cell wall arabinogalactan-protein (AGP), indicating a role for REB1 in AGP biosynthesis. We show that REB1 is allelic to ROOT HAIR DEFICIENT 1 (RHD1), one of five ubiquitously expressed genes that encode isoforms of UDP-D-glucose 4-epimerase (UGE), an enzyme that acts in the formation of UDP-D-galactose (UDP-D-Gal). The RHD1 isoform is specifically required for the galactosylation of xyloglucan (XG) and type II arabinogalactan (AGII) but is not involved either in D-galactose detoxification or in galactolipid biosynthesis. Epidermal cell walls in the root expansion zone lack arabinosylated (1-->6)-beta-D-galactan and galactosylated XG. In cortical cells of rhd1, galactosylated XG is absent, but an arabinosylated (1-->6)-beta-D-galactan is present. We conclude that the flux of galactose from UDP-D-Gal into different downstream products is compartmentalized at the level of cytosolic UGE isoforms. This suggests that substrate channeling plays a role in the regulation of plant cell wall biosynthesis.

Arabidopsis↗
PubMed2002

The role of galactose, lactose, and galactose valency in the biorecognition of N-(2-hydroxypropyl)methacrylamide copolymers by human colon adenocarcinoma cells.

PURPOSE: To examine the beta-galactoside and beta-lactoside binding capacity of three human colon-adenocarcinoma cell lines and their sugar specificity, using N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer conjugates of galactosamine, lactose, and triantennary galactose. METHODS: Three types of HPMA copolymers containing the saccharide epitopes galactosamine (P-Gal), lactose (P-Lac), or triantennary galactose (P-TriGal) were synthesized. The relationship between the content of the saccharide moieties, the valency of the galactose residues, and their biorecognition by the cell lines (Colo-205, SW-480, and SW-620) was investigated using flow cytometry and confocal fluorescence microscopy analysis. RESULTS: The binding of the glycoconjugates to the human colonadenocarcinoma cell lines was dependent on the type and the number of bound sugar residues per macromolecule. The higher the sugar contents in the HPMA copolymers, the higher the extent of binding. Although introduction of galactoside residues into the HPMA copolymer resulted in a significant increase in the binding of the copolymers to the cells, low biorecognition of the lactoside-containing HPMA copolymers by all cell lines used was observed. The trivalent galactoside-containing HPMA copolymers did not yield a notable glycoside cluster effect for the beta-galactoside-binding lectin expressed on human colon-adenocarcinoma cells. Among the various cell line little differences in the extent of binding of the glycopolymers to the cells were observed. The data on the internalization of HPMA copolymer conjugates obtained by confocal fluorescence microscopy correlated well with the flow cytometry analysis of their biorecognition by target cells. CONCLUSIONS: The lectin-mediated endocytosis of the HPMA glycoconjugates in human colon cancer cell lines suggests their potential use as targeting tools of cytotoxic drugs to colon adenocarcinoma.

Adenocarcinoma↗
PubMed1974

Multiple regulation of the galactose operon-genetic evidence for a distinct site in the galactose operon that responds to capR gene regulation in Escherichia coli K-12.

Previous results demonstrated that the capR (lon) locus, which is not linked to the gal operon, independently controls the synthesis of the gal operon enzymes and gal mRNA, i.e., galO(+)capR9 strains are derepressed 4- to 6-fold as compared to galO(+)capR(+) strains. A mutation has been isolated and localized in the galactose operator region that defines a new and distinct site of control. Mutation in this site, designated galO(capR+), causes a 4-fold increase in the galactose enzymes, galactokinase (EC 2.7.1.6) and UDP-galactose-4-epimerase (EC 5.1.3.2), in a capR(+) background. These mutants exhibit a reduced response to regulation by the unlinked regulator gene capR (lon). However, the galO(capR+) mutants are still subject to control by the galR repressor, since they can be further derepressed by growth in the presence of D-fucose. They also synthesize more galactokinase when grown in glycerol as compared to glucose. Thus there are now at least three, and probably four, sites for control of mRNA synthesis in the operator-promoter regions of the gal operon, making it one of the most complex control systems to date for a single operon in bacteria. The complexity is sufficient to accommodate models for differentiation in higher organisms that require more than one "switch" to control a single group of genes.

Alleles↗
PubMed1995

Substrate recognition domain of the Gal2 galactose transporter in yeast Saccharomyces cerevisiae as revealed by chimeric galactose-glucose transporters.

The Gal2 galactose transporter takes up galactose in yeast. A homologous glucose transporter from the same organism, Hxt2, was selected, and various chimeras between these two transporters were constructed by making use of homologous recombination in Escherichia coli. Comparison of the galactose transport activities of three series of chimeras enabled us to positively identify a crucial substrate recognition region of 101 amino acids that lies close to the carboxyl terminus of the Gal2 transporter.

Base Sequence↗
PubMed1978

Galactose metabolism in Dictyostelium discoideum. Regulation of galactose-1-phosphate-uridyl transferase during growth and development.

Dictyostelium discoideum is able to metabolize [1-14C]galactose to 14CO2 despite the observation that galactose is inhibitory with respect to growth. Galactose-1-phosphate uridyl transferase activity is present throughout growth and development and varies in activity only slightly during the entire life cycle of D. discoideum, in contrast to the rapid increase in UDP-glucose 4-epimerase activity during development. Therefore, in D. discoideum, these two enzymes of the Leloir pathway are independently regulated, unlike E. coli where these enzymes are coordinately controlled.

Dictyostelium↗
PubMed2004

Energetics of galactose- and glucose-aromatic amino acid interactions: implications for binding in galactose-specific proteins.

An aromatic amino acid is present in the binding site of a number of sugar binding proteins. The interaction of the saccharide with the aromatic residue is determined by their relative position as well as orientation. The position-orientation of the saccharide relative to the aromatic residue was found to vary in different sugar-binding proteins. In the present study, interaction energies of the complexes of galactose (Gal) and of glucose (Glc) with aromatic residue analogs have been calculated by ab initio density functional (U-B3LYP/ 6-31G**) theory. The position-orientations of the saccharide with respect to the aromatic residue observed in various Gal-, Glc-, and mannose-protein complexes were chosen for the interaction energy calculations. The results of these calculations show that galactose can interact with the aromatic residue with similar interaction energies in a number of position-orientations. The interaction energy of Gal-aromatic residue analog complex in position-orientations observed for the bound saccharide in Glc/Man-protein complexes is comparable to the Glc-aromatic residue analog complex in the same position-orientation. In contrast, there is a large variation in interaction energies of complexes of Glc- and of Gal- with the aromatic residue analog in position-orientations observed in Gal-protein complexes. Furthermore, the conformation wherein the O6 atom is away from the aromatic residue is preferred for the exocyclic -CH2OH group in Gal-aromatic residue analog complexes. The implications of these results for saccharide binding in Gal-specific proteins and the possible role of the aromatic amino acid to ensure proper positioning and orientation of galactose in the binding site have been discussed.

Amino Acids, Aromatic↗
PubMed1986

Galactose- and maltose-stimulated lipoamide dehydrogenase activities related to the binding-protein-dependent transport of galactose and maltose in toluenized cells of Escherichia coli.

The binding protein-dependent transport of galactose and maltose occurs at a reduced but significant rate in Escherichia coli cells which have undergone a mild toluenization. Dihydrolipoate and 3-acetyl-NAD produce a severalfold stimulation of these transports in the toluenized cells. In parallel to the stimulation of galactose and maltose transport by dihydrolipoate and 3-acetyl-NAD, there is a stimulation by galactose and maltose of lipoamide dehydrogenase activities which seem to be related to the binding-protein-dependent transport of these sugars. The lipoamide dehydrogenase component of the pyruvate and 2-oxoglutarate dehydrogenase complexes (the lpd gene product) is not involved in this stimulation. These results are discussed in relation to our recent studies showing a possible involvement of lipoic acid and of the 2-oxoacid dehydrogenases in the binding-protein-dependent transports.

ATP-Binding Cassette Transporters↗
PubMed1966

Galactose conversion to D-xylulose: an alternate route of galactose metabolism.

Galactose dehydrogenase, a soluble enzyme of the mammalian liver, catalyzes the conversion of galactose to galactonic acid. This reaction, together with the subsequent formation of 3-ketogalactonic acid which can be decarboxylated to yield d-xylulose, is a newly discovered pathway for the metabolism of galactosee. This pathway may account for the oxidation of galactose observed in pathients with galactosemia.

Alcohol Oxidoreductases↗
PubMed1993

Identification of a complex operator for galP1, the glucose-sensitive, galactose-dependent promoter of the Streptomyces galactose operon.

The galP1 promoter is responsible for galactose-dependent, glucose-sensitive transcription of the galactose utilization operon of Streptomyces coelicolor and Streptomyces lividans. We describe the characterization of mutations that were positioned directly upstream of the apparent transcription start site of galP1 and that resulted in deregulated expression. Certain combinations of base changes within a series of hexamers that lie within two pairs of direct repeat sequences resulted in significant expression from galP1 in the absence of inducer. These motifs are further implicated in regulation by the observation that DNA fragments containing the hexamers and direct repeat sequences resulted in increased transcription from the chromosomal copy of galP1 on multicopy plasmids in the absence of galactose. We suggest that these hexamers and direct repeat sequences constitute an operator for the negative regulation of the Streptomyces gal operon.

Base Sequence↗
PubMed1978

Simultaneous localization of an hepatic binding protein specific for galactose and of galactose-containing receptors on rat hepatocytes.

The hepatic binding protein, specific for galactose-terminated glycoproteins (asialoglycoproteins) and the receptors for the Ricinus communis lectin, specific for galactose residues (RCA1), were simultaneously localized on isolated rat hepatocytes by the gold method. The marker for the binding protein was prepared from gold granules (5 nm in diam.) labeled with ceruloplasmin and desialylated. The marker specific for galactose-containing receptors consisted of granules (17 nm in diameter) labeled with RCA1. It was established that both markers did not interact. Hepatocytes (fresh or briefly fixed with glutaraldehyde) were successively incubated with the asialoceruloplasmin and the RCA1 marker. Examination of thin sections by electron microscopy indicated that the binding protein and the RCA1 receptors were often in the proximity of each other on the plasmamembrane. Using the same technique, wheat germ agglutinin (WGA) receptors were generally found on area of the plasmamembrane poorly marked by the RCA1 gold marker. The binding of asialoceruloplasmin gold markers was studied as a function of the size of the granules. It became insignificant when the size was above 17 nm. Previous results have shown that the binding of RCA1 is low when the marker reaches 50 nm in size while WGA markers up to 75 nm are well bound by hepatocytes. It is therefore hypothesized that the binding protein and RCA1 receptors are located between glycoprotein brushes of increasing spacing while part or all of the WGA receptors are located at the periphery of the brushes.

Animals↗
PubMed1980

[Half-life of galactose in the blood plasma of lambs and sheep and the effect on various blood components after an i.v. galactose solution infusion].

Three lambs, aged between four and five weeks, and four sheep, aged one year, received infusions of galactose solutions (0.5 g galactose/kg body weight). The average half-life values were 28.7 minutes in the lambs and 59 minutes in the sheep. Average galactose concentrations, five minutes from mid-infusion, were 61 +/- 1.2 mg/100 ml of blood plasma in the lambs and 71 +/- 3.3 mg/100 ml in the sheep. The infusions caused statistically significant rises of glucose in the blood plasma of both lambs and sheep and an additional rise of fructose in the blood plasma of the sheep. In sheep galactose infusion resulted in rise of insulin in the blood plasma, within ten minutes from mid-infusion, the latter rise being statistically significant, from 53 +/- 26 microE/ml to 96 +/- 23.3 microE/ml. The lambs exhibited, as a result of the infusions, statistically significant rises of blood-borne lactate from 6.7 +/- 2.3 mg/100 ml to 16.7 +/- 1.2 mg/100 ml on average, within five minutes from mid-infusion.

Animals↗
PubMed1978

Incorporation of galactose from UDP-galactose into microsomal and Golgi membranes of rat liver.

Rough and smooth microsomes and Golgi membranes were incubated with UDP[14C]galactose and the incorporation of radioactivity into the lipid extract and into endogenous protein acceptors were measured. Antagonistic pyrophosphatases were inhibited with ATP and interference from beta-galactosidase activity was greatly decreased by carrying out the incubation at pH 7.8. After incubation the particles were centrifuged to remove free oligosaccharide residues. Radioactivity was found in the lipid extract from Golgi membranes but not from rough and smooth microsomes. This radioactivity, however, was not associated with dolichol or retinyl phosphates. The incorporation of radioactivity into proteins of the Golgi fraction was more than double than that of the microsomal fractions. In addition, the transferases in these two types of particles exhibited different properties. Trypsin treatment of intact rough microsomal vesicles, smooth vesicles and Golgi membranes removed about 5, 15 and 50%, respectively, of newly incorporated protein-bound galactose, indicating that the proportion of the newly galactosylated proteins, which are localized at the cytoplasmic surface of the membrane, is lowest in rough microsomes, intermediate in smooth, and highest in Golgi membranes.

Animals↗