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Results for “GALACTOSE”

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At least 145 records · Page 8Linked to original sources
PubMed2005

Epigallocatechin-3-gallate suppresses galactose-alpha1,4-galactose-1beta,4-glucose ceramide expression in TNF-alpha stimulated human intestinal epithelial cells through inhibition of MAPKs and NF-kappaB.

Intestinal epithelial cells (IECs) have been known to produce galactose-alpha1,4-galactose-beta1,4-glucose ceramide (Gb3) that play an important role in the mucosal immune response. The regulation of Gb3 is important to prevent tissue damage causing shiga like toxin. Epigallocatechin-3-gallate (EGCG) has been studied as anti-carcinogenic, anti-oxidant, anti-angiogenic, and anti-viral activities, and anti-diabetic. However, little is known between the expressions of Gb3 on IECs. The aim of this study was to examine the inhibitory effect of EGCG, a major ingredient of green tea, on Gb3 production via mitogen-activated protein kinases (MAPKs) and nuclear factor-kappaB (NF-kappaB) in the TNF-alpha stimulated human colon epithelial cells, HT29. To investigate how Gb3 is regulated, ceramide glucosyltransferase (CGT), lactosylceramide synthase (GalT2), and Gb3 synthase (GalT6) were analyzed by RT-PCR in HT 29 cells exposed to TNF-alpha in the presence or absence of EGCG. EGCG dose-dependently manner, inhibits TNF-alpha induced Gb3 expression by blocking in both the MAPKs and NF-kappaB pathways in HT29 cells. TNF-alpha enhanced CGT, GalT2 and GalT6 mRNA levels and EGCG suppressed the level of these enzymes enhanced by TNF-alpha treatment.

Apoptosis↗
PubMed2004

Lack of galactose-alpha-1,3-galactose expression on porcine endothelial cells prevents complement-induced lysis but not direct xenogeneic NK cytotoxicity.

The galactose-alpha-1,3-galactose (alphaGal) carbohydrate epitope is expressed on porcine, but not human cells, and therefore represents a major target for preformed human anti-pig natural Abs (NAb). Based on results from pig-to-primate animal models, NAb binding to porcine endothelial cells will likely induce complement activation, lysis, and hyperacute rejection in pig-to-human xenotransplantation. Human NK cells may also contribute to innate immune responses against xenografts, either by direct recognition of activating molecules on target cells or by FcgammaRIII-mediated xenogeneic Ab-dependent cellular cytotoxicity (ADCC). The present study addressed the question as to whether the lack of alphaGal protects porcine endothelial cells from NAb/complement-induced lysis, direct xenogeneic NK lysis, NAb-dependent ADCC, and adhesion of human NK cells under shear stress. Homologous recombination, panning, and limiting dilution cloning were used to generate an alphaGal-negative porcine endothelial cell line, PED2*3.51. NAb/complement-induced xenogeneic lysis of PED2*3.51 was reduced by an average of 86% compared with the alphaGal-positive phenotype. PED2*3.51 resisted NK cell-mediated ADCC with a reduction of lysis ranging from 30 to 70%. However, direct xenogeneic lysis of PED2*3.51, mediated either by freshly isolated or IL-2-activated human NK cells or the NK cell line NK92, was not reduced. Furthermore, adhesion of IL-2-activated human NK cells did not rely on alphaGal expression. In conclusion, removal of alphaGal leads to a clear reduction in complement-induced lysis and ADCC, but does not resolve adhesion of NK cells and direct anti-porcine NK cytotoxicity, indicating that alphaGal is not a dominant target for direct human NK cytotoxicity against porcine cells.

Animals↗
PubMed2002

Antisense suppression of l-galactose dehydrogenase in Arabidopsis thaliana provides evidence for its role in ascorbate synthesis and reveals light modulated l-galactose synthesis.

l-Galactose dehydrogenase (l-GalDH), a novel enzyme that oxidizes l-Gal to l-galactono-1,4-lactone (l-GalL), has been purified from pea seedlings and cloned from Arabidopsis thaliana. l-GalL is a proposed substrate for ascorbate biosynthesis in plants, therefore the function of l-GalDH in ascorbate biosynthesis was investigated by overexpression in tobacco and antisense suppression in A. thaliana. In tobacco the highest expressing lines had a 3.5-fold increase in extractable activity, but this did not increase leaf ascorbate concentration. Arabidopsis thaliana, transformed with an antisense l-GalDH construct, produced lines with 30% of wild-type activity. These had lower leaf ascorbate concentration when grown under high light conditions. l-Gal pool size increased in antisense transformants with low l-GalDH activity, and l-Gal concentration was negatively correlated with ascorbate. The results provide direct evidence for a role of l-GalDH in ascorbate biosynthesis. Ascorbate pool size in A. thaliana is increased by acclimation to high light, but l-GalDH expression was not affected. l-Gal accumulation was higher in antisense plants acclimated to high light, indicating that the capacity to synthesize l-Gal from GDP-mannose is increased. Because the only known function of l-GalL is ascorbate synthesis, these antisense plants provide an opportunity to investigate ascorbate function with minimal effects on carbohydrate metabolism. Measurements of other antioxidants revealed an increase in ascorbate- and pyrogallol-dependent peroxidase activity in low-ascorbate lines. As ascorbate is the major hydrogen peroxide-scavenging antioxidant in plants, this could indicate a compensatory mechanism for controlling hydrogen peroxide concentration.

Antioxidants↗
PubMed2006

Carbohydrate ligands of human C-reactive protein: binding of neoglycoproteins containing galactose-6-phosphate and galactose-terminated disaccharide.

Binding of carbohydrate ligand by human C-reactive protein (CRP), in both native form and structurally deviated form (neoCRP or mCRP), was investigated using galactose-6-phosphate (Gal6P)- and Galbeta3GalNAc-containing bovine serum albumin (BSA) derivatives. To this end, we synthesized glycosides of Gal6P and Galbeta3GalNAc that can potentially generate a terminal aldehyde group. omega-Aldehydo glycosides were then conjugated to BSA via reductive amination. Using these neoglycoproteins, we showed that: (1) Gal6P-BSA and Galbeta3GalNAc-BSA bound to both forms of CRP, the former with or without calcium and the latter only in the absence of calcium; (2) phosphate-containing ligands can be bound with or without calcium, but the binding is much stronger in the presence of calcium than in the absence, underscoring the importance of direct coordination of phosphate to two calcium ions observed in the X-ray structure of phosphorylcholine (PC)-CRP complex; (3) cross-inhibition studies further corroborated the hypothesis that binding sites of PC and sugar are contiguous; (4) while PC-BSA bound to the native CRP over a wide pH range of 4.5 to 9, all the carbohydrate ligands and protamine-BSA (poly-cation-based ligand) exhibited optimal binding at around pH 6 to 6.5; and (5) ligand-binding conformation of mCRP appears to be more fragile than that of the native CRP in the acidic media (pH < 6).

Binding Sites↗
PubMed2000

Enzymatic synthesis of UDP-(3-deoxy-3-fluoro)-D-galactose and UDP-(2-deoxy-2-fluoro)-D-galactose and substrate activity with UDP-galactopyranose mutase.

The novel UDP-sugar uridine 5'-(3-deoxy-3-fluoro-D-galactopyranosyl diphosphate) (1) and UDP-(2-deoxy-2-fluoro)-D-galactose (2) have been prepared enzymatically and tested as substrate analogues for the enzyme UDP-galactopyranose mutase (UDP-Galp mutase EC 5.4.99.9). Turnover of both 1 and 2 by UDP-Galp mutase was observed by HPLC and 19F NMR. The HPLC elution profile and 19F chemical shift of the products are consistent with the formation of the predicted furanose forms of 1 and 2. The Km values for compounds 1 and 2 were similar to those of the natural substrate UDP-Galp (0.26 mM for 1, 0.2 mM for 2, and 0.6 mM for UDP-Galp), but the values for kcat were substantially different (1.6/min for 1, 0.02/min for 2, and 1364/min for UDP-Galp). A correlation was also observed between the equilibrium yield of product formed during turnover of UDP-sugar by UDP-Galp mutase (UDP-Galp, compound 1 or compound 2), and the amount of furanose present for the free sugar at thermal equilibrium in aqueous solution, using 1H and 19F NMR spectroscopy. The implications of these results to the mechanism of the unusual enzymatic reaction are discussed.

Bacterial Proteins↗
PubMed2006

Cloning and expression analysis of a UDP-galactose/glucose pyrophosphorylase from melon fruit provides evidence for the major metabolic pathway of galactose metabolism in raffinose oligosaccharide metabolizing plants.

The Cucurbitaceae translocate a significant portion of their photosynthate as raffinose and stachyose, which are galactosyl derivatives of sucrose. These are initially hydrolyzed by alpha-galactosidase to yield free galactose (Gal) and, accordingly, Gal metabolism is an important pathway in Cucurbitaceae sink tissue. We report here on a novel plant-specific enzyme responsible for the nucleotide activation of phosphorylated Gal and the subsequent entry of Gal into sink metabolism. The enzyme was antibody purified, sequenced, and the gene cloned and functionally expressed in Escherichia coli. The heterologous protein showed the characteristics of a dual substrate UDP-hexose pyrophosphorylase (PPase) with activity toward both Gal-1-P and glucose (Glc)-1-P in the uridinylation direction and their respective UDP-sugars in the reverse direction. The two other enzymes involved in Glc-P and Gal-P uridinylation are UDP-Glc PPase and uridyltransferase, and these were also cloned, heterologously expressed, and characterized. The gene expression and enzyme activities of all three enzymes in melon (Cucumis melo) fruit were measured. The UDP-Glc PPase was expressed in melon fruit to a similar extent as the novel enzyme, but the expressed protein was specific for Glc-1-P in the UDP-Glc synthesis direction and did not catalyze the nucleotide activation of Gal-1-P. The uridyltransferase gene was only weakly expressed in melon fruit, and activity was not observed in crude extracts. The results indicate that this novel enzyme carries out both the synthesis of UDP-Gal from Gal-1-P as well as the subsequent synthesis of Glc-1-P from the epimerase product, UDP-Glc, and thus plays a key role in melon fruit sink metabolism.

Amino Acid Sequence↗
PubMed2001

D-galactose-specific sea urchin lectin sugar-specifically inhibited histamine release induced by datura stramonium agglutinin: differences between sugar-specific effects of sea urchin lectin and those of D-galactose- or L-fucose-specific plant lectins.

A new sea urchin lectin from Toxopneustes pileolus, is D(+)galactose (Gal)-, D(+)fucose (Fuc)-specific. Incubation of rat peritoneal mast cells with the lectin in the presence of 0.3 mM CaCl2 for 10 min significantly and dose-dependently inhibited the histamine release induced by N-acetyl glucosamine (GlcNAc)-specific Datura stramonium agglutinin (DSA), an activator of the Gi-protein-dependent pathway in mast cells. This inhibition by the sea urchin lectin was sugar-specifically reversed in the presence of D(+)Gal or D(+)Fuc but not L(-)Fuc. The sea urchin lectin had no effect on the histamine release induced by compound 48/80, slightly inhibited the histamine release induced by substance P and mastoparan, and slightly enhanced the histamine release induced by melittin, but these effects were not dose-dependent. Compound 48/80, substance P, mastoparan and melittin are mast cell activators without sugar residues. It is suggested that the lectin binds to D(+)Gal residues of DSA to interfere with mast cell activation induced by DSA, a glycoprotein with arabinose and Gal residues. The effects of plant lectins with affinity to D(+)Gal, N-acetyl galactosamine and/or sialic acid and L(-)Fuc on the histamine release induced by DSA, compound 48/80 and substance P were also examined.

Agglutinins↗
PubMed2002

Human and Drosophila UDP-galactose transporters transport UDP-N-acetylgalactosamine in addition to UDP-galactose.

A putative Drosophila nucleotide sugar transporter was characterized and shown to be the Drosophila homologue of the human UDP-Gal transporter (hUGT). When the Drosophila melanogaster UDP-Gal transporter (DmUGT) was expressed in mammalian cells, the transporter protein was localized in the Golgi membranes and complemented the UDP-Gal transport deficiency of Lec8 cells but not the CMP-Sia transport deficiency of Lec2 cells. DmUGT and hUGT were expressed in Saccharomyces cerevisiae cells in functionally active forms. Using microsomal vesicles isolated from Saccharomyces cerevisiae expressing these transporters, we unexpectedly found that both hUGT and DmUGT could transport UDP-GalNAc as well as UDP-Gal. When amino-acid residues that are conserved among human, murine, fission yeast and Drosophila UGTs, but are distinct from corresponding ones conserved among CMP-Sia transporters (CSTs), were substituted by those found in CST, the mutant transporters were still active in transporting UDP-Gal. One of these mutants in which Asn47 was substituted by Ala showed aberrant intracellular distribution with concomitant destabilization of the protein product. However, this mutation was suppressed by an Ile51 to Thr second-site mutation. Both residues were localized within the first transmembrane helix, suggesting that the structure of the helix contributes to the stabilization and substrate recognition of the UGT molecule.

Amino Acid Sequence↗