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PubMed2001

Roles of galactose and sulfate residues in sulfatides for their antagonistic functions in the blood coagulation system.

We previously reported that the sulfatide (galactosylceramide I3-sulfate) may have contradictory functions, namely both coagulant and anticoagulant roles in vivo: sulfatide induced giant thrombi formation when injected into rats with vein ligation, whereas no thrombi were formed when sulfatide was injected into rats without vein ligation. Rather it prolonged bleeding time. To investigate the structural features of sulfatide for both functions, a synthetic sulfatide (galactosylceramide I6-sulfate) which does not occur naturally, cholesterol 3-sulfate and ganglioside GM4 were examined together with naturally occurring sulfatide. Both sulfatides and cholesterol 3-sulfate induced giant thrombi in the rats with vein ligation within ten minutes of injection, although cholesterol 3-sulfate exhibited weaker coagulant activity than the sulfatides. On the contrary, both sulfatides significantly prolonged bleeding time but cholesterol 3-sulfate barely prolonged it when injected without vein ligation. GM4 exhibited neither coagulant nor anticoagulant activity. These results suggested that sulfate moiety in the sulfatides is essential for coagulant activity and that galactose residue enhances the activity, whereas both galactose and sulfate residues seem to be important for anticoagulant activity. This is because the sulfatides possess both residues but GM4 possesses galactose without sulfate and cholesterol 3-sulfate possesses sulfate without galactose. We previously reported that the possible mechanism of anticoagulation by sulfatide was due to its binding to fibrinogen, thereby inhibiting the conversion to fibrin. In this paper we reveal that both sulfatides inhibited thrombin activity independent of heparin cofactor II, thus providing evidence of another anticoagulation mechanism for the sulfatides.

Animals↗
PubMed2000

Increasing galactose consumption by Saccharomyces cerevisiae through metabolic engineering of the GAL gene regulatory network.

Increasing the flux through central carbon metabolism is difficult because of rigidity in regulatory structures, at both the genetic and the enzymatic levels. Here we describe metabolic engineering of a regulatory network to obtain a balanced increase in the activity of all the enzymes in the pathway, and ultimately, increasing metabolic flux through the pathway of interest. By manipulating the GAL gene regulatory network of Saccharomyces cerevisiae, which is a tightly regulated system, we produced prototroph mutant strains, which increased the flux through the galactose utilization pathway by eliminating three known negative regulators of the GAL system: Gal6, Gal80, and Mig1. This led to a 41% increase in flux through the galactose utilization pathway compared with the wild-type strain. This is of significant interest within the field of biotechnology since galactose is present in many industrial media. The improved galactose consumption of the gal mutants did not favor biomass formation, but rather caused excessive respiro-fermentative metabolism, with the ethanol production rate increasing linearly with glycolytic flux.

Bacterial Proteins↗
PubMed1975

Galactose metabolism in relation to cataract formation in marsupials.

Erythrocytic galactokinase and/or galactose-1-phosphate uridyl transferase activity were low in many species of marsupials. However, cataract formation was observed only in pouch-young members of these species when reared on cow's milk. The galactose tolerance of young kangaroos was found to be greatly impaired, but improved rapidly and markedly at the stage of which the definitive structure of the ruminant type of stomach as in adults is formed. The combination of high absorption of galactose and low levels of galactokinase and/or transferase thus appears to determine the predisposition of pouch-young marsupials to galactose cataractogenesis.

Adult↗
PubMed1970

Biosynthesis of the carbohydrate portion of immunoglobulins. Kinetics of synthesis and secretion of [3H] leucine-, [3H] galactose- and [3H] mannose-labelled myeloma protein by two plasma-cell tumours.

The kinetics of incorporation of leucine, galactose and mannose into intracellular and secreted myeloma protein, MOPC 21 IgG(1) and MOPC 46 kappa-type light chain, by cell suspensions of two myeloma plasma-cell tumours, MOPC 21 and MOPC 46, were similar. Radioactive galactose was incorporated to over 90% into galactose residues of intracellular and secreted protein, mannose to over 90% into glucosamine and mannose residues of intracellular protein and to over 90% into glucosamine, mannose and fucose residues of secreted protein, but not into galactose residues. The results show that specific residues in the carbohydrate portion of myeloma proteins can be labelled by specific radioactive monosaccharides, and suggest that fucose residues are added, while myeloma protein is in its final stage of secretion from the plasma cell. The kinetics of incorporation indicate at least three sequential precursor-product relationships between different intracellular forms and the secreted form of myeloma protein.

Animals↗
PubMed1976

Studies on the purification and properties of UDP-galactose glycoprotein galactosyltransferase from rat liver and serum.

1. Rat liver microsomal preparations incubated with 200mM-NaCl at either 0 or 30 degrees C released about 20-30% of the membrane-bound UDP-galactose-glycoprotein galactosyl-transferase (EC 2.4.1.22) into a 'high-speed' supernatant. The 'high-speed' supernatant was designated the 'saline wash' and the galactosyltransferase released into this fraction required Triton X-100 for activation. It was purified sixfold by chromatography on Sephadex G-200, and appeared to have a higher molecular weight than the soluble serum enzyme. 2. Rat serum galactosyltransferase was purified 6000-7000-fold by an affinity-chromatographic technique using a column of activated Sepharose 4B coupled with alpha-lactalbumin. The purified enzyme ran as a single broad band on polacrylamide gels and contained no sialytransferase, N-acetylglucosaminyltransferase and UDP-galactose pyrophosphatase activities. 3. The highly purified enzyme had properties similar to those of both soluble and membrane-bound galactosyltransferase. It required 0.1% Triton X-100 for stabilization, but lost activity on freezing. The enzyme had an absolute requirement for Mn2+, not replaceable by Ca2+, Mg2+, Zn2+ or Co2+. It was active over a wide pH range (6-8) and had a pH optimum of 6.8. The apparent Km for UDP-galactose was 12.5 x 10(-6) M. Alpha-Lactalbumin had no appreciable effect on UDP-galactose-glycoprotein galactosyltransferase, but it increased the specificity for glucose rather than for N-acetylglucosamine, thus modifying the enzyme to a lactose synthetase. 4. The possibility of a conversion of higher-molecular-weight liver enzyme into soluble serum enzyme is discussed, especially in relation to the elevated activities of this and other glycosyltransferases in patients with liver diseases.

Acetylglucosamine↗
PubMed1977

Effects of dolichol monophosphate on galactose incorporation into glycoconjugates of cell cultures.

Cultured-cell homogenates catalysed the incorporation of galactose from UDP-galactose into protein and sphingolipid acceptors. Dolichol monophosphate stimulated the incorporation of galactose into glycoproteins, but it did not affect the rate of glycosylation of either exogenous or endogenous glycosphingolipids. It is proposed that, under certain conditions, galactose may be incorporated into glycoproteins via polyisoprenol intermediates, as is the case with N-acetylglucosamine and mannose.

Clone Cells↗
PubMed1983

The association of proton movement with galactose transport into subcellular membrane vesicles of Escherichia coli.

1. Subcellular membrane vesicles were prepared from a strain of Escherichia coli constitutive for the GalP galactose-transport system. 2. The addition of substrates of the GalP transport system to vesicle suspensions promoted alkaline pH changes, which provided direct evidence for the coupling of sugar and proton transport. 3. Respiration-energized galactose transport was progressively inhibited at pH values above 6.0, and was abolished by agents that render the membrane permeable to protons. 4. The combined effects of valinomycin, the nigericin-like compound A217 and pH on galactose transport suggested that both delta pH and delta psi components of the protonmotive force contributed to energization of galactose transport. 5. These results substantiate the conclusion that the GalP transport system operates by a chemiosmotic mechanism.

Biological Transport, Active↗
PubMed1988

A novel aspect of the inhibition by arsenicals of binding-protein-dependent galactose transport in gram-negative bacteria.

The inhibitory effects of arsenate and arsenite on binding-protein-dependent transport systems are reconsidered. It is shown that arsenate inhibits binding-protein-dependent galactose transport in proteoliposomes energized either by dihydrolipoamide and NAD+ or by a membrane potential (under conditions where ATP metabolism is not implicated); this result is in contradiction with the current interpretation of arsenate inhibition of binding-protein-dependent transport systems (which is based on ATP depletion) and can be explained by reference to the recently discovered ATP inhibition of the binding-protein-dependent galactose transport. In whole cells, the greater inhibition by arsenate of lipoamide-dependent transport than of protonmotive-force-dependent transport may be explained by a modification by arsenate of the pools of several compounds metabolized by 2-oxo-acid dehydrogenases (which have been implicated in binding-protein-dependent transport). The inhibition of binding-protein-dependent galactose transport by arsenite is probably linked to the inhibition by arsenite of the galactose-stimulated lipoamide dehydrogenase activity implicated in this transport and is reminiscent of the known arsenite inhibition of lipoamide dehydrogenases.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1979

Changes in blood glucose and plasma insulin after intravenous galactose in human injury.

1. The increase in blood glucose after intravenous galactose was measured at 6--8 h and 14 days after hip replacement (14 patients) and accidental injury (14 patients). 2. After hip replacement there was a greater rise of glucose after galactose on the day of the operation than on recovery, despite basal hyperglycaemia. This earlier period was also associated with inappropriately low insulin concentrations for the prevailing glucose concentration, and hyperketonaemia (13 out 14 patients). 3. After accidental injury patients with initial hyperketonaemia (nine out of 14) also had a greater rise of blood glucose after galactose than on recovery and had relative insulin deficiency; in contrast those who were initially normoketonaemic (five out of 14) showed a rise in glucose comparable with that after recovery and basal insulin concentrations more appropriate to the existing glucose concentration. 4. It is concluded that in most subjects after injury hepatic glucose release after galactose administration is not suppressed despite hyperglycaemia.

Adolescent↗
PubMed1996

The relationship between exposed galactose and N-acetylglucosamine residues on IgG in rheumatoid arthritis (RA), juvenile chronic arthritis (JCA) and Sjögren's syndrome (SS).

The relationship between exposed galactose and N-acetylglucosamine on IgG in RA, JCA and SS was investigated. This was achieved using IgG isolated from serum where the levels of galactose and N-acetylglucosamine (GlcNAc) were detected using biotinylated lectins. Galactose and GlcNAc on IgG from patients with RA and JCA are inversely related, but in contrast, in SS, galactose expression on IgG decreased while GlcNAc expression remained similar to normal levels. Alterations in IgG glycosylation are closely associated with the development of adult and juvenile chronic arthritis and SS, but the changes involved are different in RA compared with SS, suggesting that the precise pattern of exposed sugars is associated with different rheumatological diseases.

Acetylglucosamine↗
PubMed1999

[13C]-Galactose breath test: correlation with liver fibrosis in chronic hepatitis C.

BACKGROUND: The galactose elimination capacity test is a quantitative liver function test that has been shown to be a potential surrogate marker for death in advanced chronic liver diseases. However, this test lacks sensitivity in early liver disease. The goal of this study was to evaluate a [13C]-galactose breath test (GBT) in a population of patients with chronic hepatitis C. DESIGN: The GBT was performed in 10 control subjects and 50 patients with chronic hepatitis C; the results were compared with the METAVIR pathological scoring of liver biopsy specimens and with standard biochemical liver function tests. RESULTS: In 10 patients, oral vs. intravenous administration of galactose yielded similar results for the GBT (3.01% +/- 0.12% dose h-1 for oral galactose vs. 2.98 +/- 0.21 for intravenous). The GBT was then performed orally in the remaining 40 patients and 10 control subjects. A significant difference was observed between control subjects and patients (4.51% +/- 0.18% vs. 2.97% +/- 0.14% dose h-1, P < 0.0001). A significant difference for GBT results was observed between each fibrosis stage, but not with regard to the activity score. CONCLUSIONS: The GBT results are dependent on the severity of liver fibrosis in chronic hepatitis C. Further studies are needed to evaluate the usefulness of the GBT for the follow-up of chronic hepatitis C.

Administration, Oral↗
PubMed1973

Induction of lymphocyte transformation by sequential treatment with neuraminidase and galactose oxidase.

Treatment of mouse-spleen cells with galactose oxidase (EC 1.1.3.9) after incubation with neuraminidase (EC 3.2.1.18) induced extensive blastogenesis. Treatment of the cells with galactose oxidase before incubation with neuraminidase had very little stimulatory effect. Either of these enzymes alone had practically no effect on the cells. The lymphocyte transformation induced by galactose oxidase in neuraminidase-treated cells was decreased upon reacting the cells with borohydride or hydroxylamine, whereas treatment with these compounds did not affect transformation of cells by concanavalin A. It is suggested that galactosyl residues exposed by the action of neuraminidase on the cell membrane are oxidized by galactose oxidase, and the aldehyde moiety thus formed is involved in the induction of blastogenesis.

Alcohol Oxidoreductases↗
PubMed1976

Receptor interactions in a signalling system: competition between ribose receptor and galactose receptor in the chemotaxis response.

Galactose and ribose receptors are shown to compete for a common site by comparing the specificities of the purified receptors with the specificity of the whole organism response. Ribose does not bind to the purified galactose receptor but inhibits the in vivo galactose response. A mutant lacking the ribose receptor shows no inhibition of the galactose response even at very high ribose concentrations. The results can be explained by a mechanism involving (a) a ligand-induced conformational change in the receptor which produces a combining site with affinity for the molecule that serves as a first component of the signalling system and (b) a limited number of such first component molecules that cannot bind both receptors simultaneously. The mechanism may have considerable generality for sensory, hormonal, and transport systems.

Allosteric Regulation↗
PubMed1979

Identification of a methyl-accepting chemotaxis protein for the ribose and galactose chemoreceptors of Escherichia coli.

The ribose and galactose chemoreceptors of Escherichia coli have previously been identified as the ribose- and galactose-binding proteins. We now report the discovery of a methyl-accepting chemotaxis protein that functions in the transfer of receptor signals from these two binding proteins to the flagella. This protein is distinct from previously described methyl-accepting chemotaxis proteins. Its level of methylation is influenced by D-ribose, D-galactose, and certain structural analogues of them. This methyl-accepting protein is required for chemotaxis toward those attractants; mutants in the trg gene, which do not methylate this protein, are devoid of taxis toward D-ribose, D-galactose, and their analogues. In addition, methylation of the methyl-accepting protein in response to each of these attractants requires the appropriate binding protein. The binding protein's chemoreceptor function is required for such methylation, but its transport activity is not. Because the function of this methyl-accepting chemotaxis protein involves two of the best-characterized chemoreceptors, the discovery of this protein represents a promising base for further study of the linkage between chemoreceptors and flagella in bacteria.

Bacterial Proteins↗
PubMed1979

Gene expression of an Escherichia coli ribosomal RNA promoter fused to structural genes of the galactose operon.

The promoter region of the rrnB ribosomal RNA gene of Escherichia coli has been ligated within the epimerase gene (galE) of the galactose operon in a lambda phage vector. The recombinant lambda phage has been characterized by restriction mapping and assays of both galK (galactokinase) gene activity and galactose messenger RNA hybridization. In such lyosgens, expression of the fused galactose operon occurs as a function of growth rate in a manner characteristic of ribosomal RNA gene expression and is subject to stringent control by amino acid availability for protein synthesis. Galactose messenger RNA arising from the ribosomal promoter is not as metabolically stable as ribosomal RNA.

Bacteriophage lambda↗
PubMed2003

Cu(I)-dependent biogenesis of the galactose oxidase redox cofactor.

Galactose oxidase is a copper metalloenzyme containing a novel protein-derived redox cofactor in its active site, formed by cross-linking two residues, Cys228 and Tyr272. Previous studies have shown that formation of the tyrosyl-cysteine (Tyr-Cys) cofactor is a self-processing step requiring only copper and dioxygen. We have investigated the biogenesis of cofactor-containing galactose oxidase from pregalactose oxidase lacking the Tyr-Cys cross-link but having a fully processed N-terminal sequence, using both Cu(I) and Cu(II). Mature galactose oxidase forms rapidly following exposure of a pregalactose oxidase-Cu(I) complex to dioxygen (t(1/2) = 3.9s at pH7). In contrast, when Cu(II) is used in place of Cu(I) the maturation process requires several hours (t(1/2) = 5.1 h). EDTA prevents reaction of pregalactose oxidase with Cu(II) but does not interfere with the Cu(I)-dependent biogenesis reaction. The yield of cross-link corresponds to the amount of copper added, although a fraction of the pregalactose oxidase protein is unable to undergo this cross-linking reaction. The latter component, which may have an altered conformation, does not interfere with analysis of cofactor biogenesis at low copper loading. The biogenesis product has been quantitatively characterized, and mechanistic studies have been developed for the Cu(I)-dependent reaction, which forms oxidized, mature galactose oxidase and requires two molecules of O2. Transient kinetics studies of the biogenesis reaction have revealed a pH sensitivity that appears to reflect ionization of a protein group (pKa = 7.3) at intermediate pH resulting in a rate acceleration and protonation of an early oxygenated intermediate at lower pH competing with commitment to cofactor formation. These spectroscopic, kinetic, and biochemical results lead to new insights into the biogenesis mechanism.

Aspergillus niger↗
PubMed2004

Determinants of function and substrate specificity in human UDP-galactose 4'-epimerase.

UDP-galactose 4'-epimerase (GALE) interconverts UDP-galactose and UDP-glucose in the final step of the Leloir pathway. Unlike the Escherichia coli enzyme, human GALE (hGALE) also efficiently interconverts a larger pair of substrates: UDP-N-acetylgalactosamine and UDP-N-acetylglucosamine. The basis of this differential substrate specificity has remained obscure. Recently, however, x-ray crystallographic data have both predicted essential active site residues and suggested that differential active site cleft volume may be a key factor in determining GALE substrate selectivity. We report here a direct test of this hypothesis. In brief, we have created four substituted alleles: S132A, Y157F, S132A/Y157F, and C307Y-hGALE. While the first three substitutions were predicted to disrupt catalytic activity, the fourth was predicted to reduce active site cleft volume, thereby limiting entry or rotation of the larger but not the smaller substrate. All four alleles were expressed in a null-background strain of Saccharomyces cerevisiae and characterized in terms of activity with regard to both UDP-galactose and UDP-N-acetylgalactosamine. The S132A/Y157F and C307Y-hGALE proteins were also overexpressed in Pichia pastoris and purified for analysis. In all forms tested, the Y157F, S132A, and Y157F/S132A-hGALE proteins each demonstrated a complete loss of activity with respect to both substrates. In contrast, the C307Y-hGALE demonstrated normal activity with respect to UDP-galactose but complete loss of activity with respect to UDP-N-acetylgalactosamine. Together, these results serve to validate the wild-type hGALE crystal structure and fully support the hypothesis that residue 307 acts as a gatekeeper mediating substrate access to the hGALE active site.

Alleles↗
PubMed2006

Comparison of exogenous glucose, fructose and galactose oxidation during exercise using 13C-labelling.

Six subjects exercised for 120 min on a cycle ergometer (65 (se 3) % VO2max) when ingesting a placebo or glucose, fructose or galactose (100 g in 1000 ml water) labelled with 13C. The oxidation of energy substrates including exogenous hexoses was compared using indirect respiratory calorimetry and 13CO2 production at the mouth. Total carbohydrate progressively decreased and total fat oxidation increased over the 120 min exercise period in the four experimental situations. During the 120 min of exercise, the amount of fructose oxidized (38.8 (se 2.6) g; 9.0 (se 0.6) % energy yield) was not significantly (approximately 4 %) lower than that of exogenous glucose (40.5 (se 3.4) g; 9.2 (se 0.8) % energy yield), while that of galactose (23.7 (se 3.5) g; 5.5 (se 0.9) % energy yield) was only 59 % and 61 % that of glucose and fructose, respectively. When compared with the placebo, the ingestion and oxidation of the three hexoses did not significantly modify fat oxidation or total carbohydrate oxidation, but it significantly reduced (9-13 %) endogenous carbohydrate oxidation. The present data indicate that fructose and exogenous glucose ingested during exercise could be oxidized at a similar rate, but that the oxidation rate of galactose was only approximately 60 % that of the exogenous glucose and fructose, presumably because of a preferential incorporation of galactose into liver glycogen (Leloir pathway). The reduction in endogenous carbohydrate oxidation was, however, similar with the three hexoses.

Administration, Oral↗