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At least 1,531 records · Page 85Linked to original sources
PubMed1995

Enzyme-assisted synthesis of a bivalent high-affinity dodecasaccharide inhibitor of mouse gamete adhesion. The length of the chains carrying distal alpha 1,3-bonded galactose residues is critical.

Proposing to study the molecular mechanisms of mouse gamete adhesion with the aid of high affinity adhesion inhibitors of saccharide nature, we report here the enzymatic synthesis of a bivalent oligosaccharide Gal alpha 1-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4GlcNAc beta 1-3(Gal alpha 1-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4GlcNAc beta 1-6)Gal beta 1-4GlcNAc (4), consisting of two long arms that link together two distal alpha 1,3-galactose residues. Binding data reported elsewhere (E. Litscher et al., Biochemistry, 1995, 34, 4662-4669) show that 4 is a high affinity inhibitor of mouse gamete adhesion in vitro (IC50 = 9 microM), while a related octasaccharide Gal alpha 1-3Gal beta 1-4GlcNAc beta 1-3(Gal alpha 1-3Gal beta 1-4GlcNAc beta 1-6)Gal beta 1-4GlcNAc, consisting of two short arms is of very low inhibitory activity. The data highlight the importance of the two alpha-galactose residues of 4, and the length of the sugar chains joining them.

Animals↗
PubMed1992

Regulation of open complex formation at the Escherichia coli galactose operon promoters. Simultaneous interaction of RNA polymerase, gal repressor and CAP/cAMP.

The regulation of open complex formation at the Escherichia coli galactose operon promoters by galactose repressor and catabolite activator protein/cyclic AMP (CAP/cAMP) was investigated in DNA-binding and kinetic experiments performed in vitro. We found that gal repressor and CAP/cAMP bind to the gal regulatory region independently, resulting in simultaneous occupancy of the two gal operators and the CAP/cAMP binding site. Both CAP/cAMP and gal repressor altered the partitioning of RNA polymerase between the two overlapping gal promoters. Open complexes formed in the absence of added regulatory proteins were partitioned between gal P1 and P2 with occupancies of 25% and 75%, respectively. CAP/cAMP caused open complexes to be formed nearly exclusively at P1 (98% occupancy). gal repressor caused a co-ordinated, but incomplete, switch in promoter partitioning from P1 to P2 in both the absence and presence of CAP/cAMP. We measured the kinetic constants governing open complex formation and decay at the gal promoters in the absence and presence of gal repressor and CAP/cAMP. CAP/cAMP had the largest effect on the kinetics of open complex formation, resulting in a 30-fold increase in the apparent binding constant. We conclude that the regulation of open complex formation at the gal promoters does not result from competition between gal repressor, CAP/cAMP and RNA polymerase for binding at the gal operon regulatory region, but instead results from the interactions of the three proteins during the formation of a nucleoprotein complex on the gal DNA fragment. Finally, we present a kinetic model for the regulation of open complex formation at the gal operon.

Base Sequence↗
PubMed1988

Statil-sensitive polyol formation in nerve of galactose-fed mice.

The sciatic nerve of diabetic C57BL/Ks mice did not accumulate either sorbitol or fructose despite elevated nerve glucose levels, nor did they show a depletion of free myo-inositol. Galactose feeding of both nondiabetic and diabetic mice for five days resulted in marked accumulations of dulcitol in nerve indicating polyol forming activity. Levels of myo-inositol showed small elevations in nerves of galactose-fed mice which reached significance when compared to diabetic mice fed the standard diet. Dulcitol accumulation was prevented by concurrent administration of the aldose reductase inhibitor Statil, but this did not prevent the increased levels of myo-inositol.

Aldehyde Reductase↗
PubMed1995

Identification of galactitol 2-phosphate and galactitol 3-phosphate in the lens of galactose-fed rats.

Production of unusual phosphorylated metabolites in the lens is one of several changes caused by hyperglycemia. Sorbitol 3-phosphate (Sor-3P) and fructose 3-phosphate (Fru-3P) are two such compounds identified in the diabetic lens, and galactitol 2-phosphate (Gal-2P) and galactitol 3-phosphate (Gal-3P) are identified here in the galactosemic lens. These new compounds are the first example of galactitol metabolism in mammalian tissue other than liver. Sor-3P and Fru-3P are also present in the galactosemic lens, apparently synthesized directly from their precursors, sorbitol and fructose, which are elevated in the lens due to increased flux of glucose through the aldose reductase (AR) pathway. The NADPH necessary to support this increased flux is derived from activation of the hexose monophosphate shunt (HMPS), which is clearly demonstrated by a large increase in the concentration of sedoheptulose 7-phosphate (Sed-7P), a HMPS-specific metabolite. Additionally, during 3 weeks of galactose feeding, there is a dramatic increase in lenticular concentrations of galactitol, sorbitol, galactose, and fructose and a sharp decrease in inositol. Glucose remains unchanged. A precipitous loss of both phosphorylated and nonphosphorylated metabolites occurs after 3 weeks, possibly due to lens rupture.

Animals↗
PubMedDate not supplied

Galactose and cataract.

Galactosemia is a disorder caused by a deficiency of any one of three possible enzymes involved in the metabolism of galactose: galactokinase, transferase or epimerase. Any single deficient enzyme can result in cataract through the accumulation of galactitol in the lens. The ophthalmologist may play an important role in this disease, since early recognition of cataract development followed by the initiation of a galactose-free diet may lead to clearing of lenticular opacities. The clinical and laboratory findings that distinguish the three enzyme deficiency disorders of galactosemia are discussed. The biochemical genetics of each enzyme also are reviewed, along with the recent evidence linking heterozygous galactokinase deficiency and presenile cataract.

Animals↗
PubMed1979

Resolution of D- and L-galactose peracetates as their bis(ethyl L-lactate) acetals by gas-liquid chromatography.

Reaction between ethyl L-lactate and each of a pair of sugar enantiomers, the peracetylated D-galactose and L-galactose diethyldithioacetals, produced two acyclic diasterioisomers. They could be separated by conventional gas-liquid chromatography. The corresponding fucose diastereomers were also separated. This process should make it possible to develop a general analytical method by which small amounts of enantiomeric sugars can be identified and their quantities measured.

Chromatography, Gas↗
PubMed1984

Selective spin labeling of terminal galactose and N-acetylgalactosamine residues on the membrane surface of erythrocytes.

A method to selectively spin label galactose and N-acetylgalactosamine residues of erythrocyte membrane glycoconjugates is described. The method is based on the activation of the C-6 CH2OH group of these two sugars by galactose oxidase followed by reductive amination with 2,2,6,6-tetramethyl-4-aminopiperidine-1-oxyl in the presence of a mild reducing agent, NaBH3CN. The extent and distribution of the spin labeling suggest that the major sialoglycoprotein, PAS-1, incorporates the greatest amount of spin label while the glycolipids incorporate less than 10% of the spin label.

Acetylgalactosamine↗
PubMed1994

Demonstration of the interaction between the CD23 molecule and the galactose residue of glycoproteins.

The CD23 molecule is a low-affinity receptor for IgE and has a marked homology in amino acid sequence with C-type animal lectins, including asialoglycoprotein receptor. We tested whether the CD23 antigen can indeed interact with the sugar chain of glycoproteins. Detergent extract of the membrane component from Epstein-Barr Virus (EBV)-transformed human B-cell line, L-KT9 cells, was incubated with asialofetuin (ASF)-coupled Sepharose, and bound proteins were effectively eluted by 0.3 M lactose or galactose which were among the competitive sugars tested. In this eluate, the CD23 molecule was detected by an immunoblotting technique. Because fetuin has both an N- and O-type sugar chain on the molecule, we tested which type of sugar chain can interact with CD23. The CD23 molecule interacted with asialocasein having a sugar chain with the Gal-GalNAc structure with asialobovine submaxillary mucin having the GalNAc structure, and also with ASF; however, it faintly interacted with ASF after removal of the O-type sugar chain by beta-elimination. These results showed that the CD23 molecule can, indeed, interact with the galactose residue, especially with the Gal-GalNAc rather than the Gal-GlcNAc structure of the terminal sugar chain of glycoproteins.

Acetylgalactosamine↗
PubMed1983

Associative properties of the Escherichia coli galactose-binding protein and maltose-binding protein.

The ligand-binding characteristics of periplasmic galactose-binding protein and maltose-binding protein of Escherichia coli are analyzed. The saturation function was decreased upon increasing protein concentration and the monomer-dimer equilibrium was shifted towards the monomeric protein form upon an increase of the ligand concentration. An association constant K0 = 6 X 10(8) M-1 was found for the galactose-binding protein. These data fit a monomer-dimer system in equilibrium, in which the monomer has a higher affinity for the ligand.

ATP-Binding Cassette Transporters↗
PubMed1990

Use of quantitative liver function tests--caffeine clearance and galactose elimination capacity--after orthotopic liver transplantation.

To establish the potential value of quantitative tests of liver function following orthotopic liver transplantation (OLT), a total of 100 determinations of caffeine clearance (CafCl) and galactose elimination capacity (GEC) were made in ten OLT recipients early in the post-operative course (days 2, 4, 6, 8 and 12) and later when clinically stable (3-12 months). Values were compared with a reference range in six normal volunteers in whom it was shown that the standard doses of caffeine (125 mg) and galactose (0.5 g per kg body weight) could be given together without interference. In orthotopic liver transplantation recipients initial GEC and CafCl measurements showed no correlation with peri-operative blood loss, donor ischaemia time, initial bile flow or survival. Throughout the early post-operative period, there were wide inter- and intra-individual variations in both CafCl (17-fold range from 0.16 to 2.7 ml.min-1.kg-1) and GEC (2.4-fold range from 5.1 to 12 mg.min-1.kg-1), but the only correlation of test values with standard liver function tests results was between GEC and gamma-glutamyltranspeptidase. However, GEC values fell by 19% during periods of acute rejection and there was an inverse correlation of GEC with white cell count probably related to sepsis.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Receptor-mediated endocytosis of galactose and mannose exposing ligands: an electron microscopic study on adult and neonatal cultured rat hepatocytes.

We compared the receptor-mediated endocytosis for galactose and mannose exposing ligands in primary cultures of hepatocytes from newborn and adult rats. The endocytic pathway was revealed ultrastructurally using colloidal gold particles coupled to lactosylated bovine serum albumin and invertase. The binding activity on the cell surfaces is observed by keeping the cells at 4 degrees C. For both ligands used, the binding capacity for hepatocytes from adult rats was greater than for neonatal cultured cells. Increasing the temperature to 37 degrees C, we observed that the protein-gold complexes entered the intracellular endocytic organelles. Within 5-15 min, the marker was confined in vesicles close to the cell surface and in the endosome, while after 60 min, the marker is found in lysosome-like compartments. We found that the process of endocytosis is similar for galactose and mannose exposing ligands. The organelles involved in the process of endocytosis in newborn cultured hepatocytes are not different in shape from those of cultured cells of adult rats, but the process of internalization is slower.

Aging↗
PubMed1983

Galactose-particle receptor on liver macrophages. Quantitation of particle uptake.

Liver macrophages have been shown previously to bind and ingest gold particles coated with asialoglycoproteins via a N-acetyl-D-galactosamine / D-galactose-specific lectin (Kolb-Bachofen, V., Schlepper-Schäfer, J., Vogell, W. and Kolb, H. (1982) Cell 29, 859-866). We present here a quantitative analysis of lectin-dependent particle endocytosis. We used a conjugate of asialofetuin with colloidal gold as ligand, the cellular uptake of which could be followed by spectrophotometry. Freshly isolated Kupffer cells from the rat liver ingest asialofetuin at a rate of approx. 4200 particles/cell per min. Uptake is inhibited by saccharides related in structure to D-galactose and depends on the presence of Ca2+. The rate of endocytosis is zero below 10 degrees C, shows a modest increase until 20 degrees C and a steep increase between 20 and 37 degrees C. Uptake is energy-dependent and strongly inhibited by cytochalasin B but only slightly by colchicine.

Animals↗
PubMed1993

Clearance of circulating gamma-glutamyltransferase by the hepatic galactose receptor. Variability in clearance rate due to carbohydrate heterogeneity of the enzyme.

The clearance and organ uptake of gamma-glutamyltransferase was studied by injecting the purified human liver enzyme intravenously in the rat. The enzyme was almost exclusively taken up by liver hepatocytes with a rapid initial uptake. The clearance was significantly inhibited by asialofetuin as well as by galactose and fucose. The uptake of neuraminidase-treated enzyme was much more rapid than that of the native enzyme. Subfractions of gamma-glutamyltransferase obtained by lectin affinity chromatography revealed significant differences in clearance rates. The data strongly indicates that the uptake of circulating gamma-glutamyltransferase involves the galactose (asialo-glycoprotein) receptor of the parenchymal cells, and that the heterogeneity of gamma-glutamyltransferase results in varying clearance rates.

Animals↗
PubMed1982

In vivo ageing of rat erythrocytes and cell surface labeling by D-galactose oxidase and sodium borotritide.

1. Young and old rat erythrocytes, separated in vitro, according to their age in vivo, were radioactively labeled at the cell surface D-galactosyl and 2-acetamido-2-deoxy-D-galactose (Gal and GalNAC) residues by treatment with D-galactose oxidase, followed by reduction with sodium borotritide: 2. The number of labeled surface residues per erythrocyte was found to be 0.52 X 10(6) +/- 0.08 X 10(6) for young, 0.38 X 10(6) +/- 0.05 X 10(6) for middle-aged and 0.32 X 10(6) +/- 0.05 X 10(6) for old, indicating a significant decrease of these surface Gal and GalNAC residues during ageing. 3. Qualitative changes were observed between the sodium dodecyl sulfate electrophoretic patterns of young, middle-aged and old labeled erythrocytes. 4. Quantitative changes were previously observed between the electrophoretic patterns of the labeled glycoproteins from young, middle-aged and old human labeled erythrocytes. 5. It is concluded that some of the changes occurring during in vivo ageing of rat and of human erythrocytes are different.

Animals↗
PubMed1989

Purification and characterization of a galactose-binding lectin from the skin mucus of the conger eel Conger myriaster.

1. A galactose-binding lectin was purified from the skin mucus of the conger eel Conger myriaster by affinity chromatography and HPLC. 2. The lectin was a simple protein having the same two subunits with a mol. wt of 12,500 and a N-terminal amino acid of phenylalanine. 3. Electrofocusing suggested that the purified lectin was composed of several isolectins. 4. From the ultraviolet difference spectra attributable to tryptophanyl residues in the binding site, the binding constant of the lectin for D-galactose was estimated to be 5.3 x 10(3)/M.

Animals↗
PubMed1982

Reduction of the sialic acid and galactose concentrations in erythrocyte membranes in alcoholics.

The sialic acid and galactose concentrations in erythrocyte membranes were examined in 32 and 17 alcoholics respectively, during current abuse, and the sialic acid concentration in 10 patients after one and four weeks of abstention. During current alcohol abuse the concentrations of these two surface carbohydrates were decreased by an average of 10% and 16% respectively, when compared to matched, healthy controls (p less than 0.0005). After one and four weeks of abstention the sialic acid values were not significantly different from those of the controls suggesting that the abnormal cells were eliminated within one week after cessation of alcohol intake. No correlations were found between the sialic acid or galactose concentrations and peripheral red cell characteristics or serum liver enzyme levels. Hemolysis in isotonic Tris was significantly increased during current abuse, and was highly dependent on the sialic acid concentration at one particular stage of Tris-induced lysis. The mechanism behind the change of the oligosaccharide concentration of the membrane may either be increased hydrolytic cleavage or inhibition of the synthesis of glycoproteins and glycolipids. Previous similar findings in serum transferrin in alcoholics and in synaptosomes from young rat brain after ethanol exposure indicate that glycoprotein and glycolipid metabolism may be an important target, directly or indirectly, in the biological actions of ethanol.

Adult↗
PubMed1993

Alternate interactions of the D-galactose-specific yeast lectin Kb-CWL I with sensitive yeast strains.

In vitro growth assays with a purified D-galactose-specific lectin Kb-CWL I extracted from Kluyveromyces bulgaricus showed marked antifungal effects on 9 of 12 test strains belonging to the genera Kluyveromyces, Saccharomyces, Pichia, Candida, Rhodotorula and Schizosaccharomyces. The inhibition of growth was proportional to the lectin concentration (0.04 and 0.08 mg ml-1) in the culture medium. Under the test conditions, K. bulgaricus, K. lactis and S. bayanus were consistently agglutinated without growth inhibition. D-Galactose, the inhibitory sugar of the cell aggregation activity, did not abolish the antifungal effects of the lectin Kb-CWL I on other yeast strains tested. In C. albicans and C. tropicalis, the lectin influenced the dimorphism of these strains and stimulated germ tube formation.

Antifungal Agents↗
PubMed1981

Expression of Pseudomonas fluorescens D-galactose dehydrogenase in E. coli.

To investigate the heterologous expression of Pseudomonas genes in Escherichia coli we have cloned P. fluorescens DNA in an E. coli [cosmid] system. A colony bank representing the whole P. fluorescens chromosome was screened immunologically using a modification of the method described by Broome and Gilbert (1978). Radioactive labelling of the antibodies was replaced by conjugation with horseradish peroxidase. Among 523 E. coli colonies one was D-galactose dehydrogenase-positive. The expression of this enzyme in primary clones was lower than in the uninduced Pseudomonas. Subcloning of the D-galactose dehydrogenase gene, in vitro mutagenesis of the DNA, and coupling to a strong E. coli promoter yielded an E. coli strain that produces 90 times more of the enzyme than the induced P. fluorescens.

Bacterial Proteins↗