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At least 1,423 records · Page 79Linked to original sources
PubMed1999

Structures of the complexes of peanut lectin with methyl-beta-galactose and N-acetyllactosamine and a comparative study of carbohydrate binding in Gal/GalNAc-specific legume lectins.

The crystal structures of complexes of peanut lectin with methyl-beta-galactose and N-acetyllactosamine have been determined at 2.8 and 2.7 A, respectively. These, and the complexes involving lactose and the T-antigenic disaccharide reported previously, permit a detailed characterization of peanut-lectin-carbohydrate association and the role of water molecules therein. The water molecules in the combining site are substantially conserved in the four complexes. The role of interacting sugar hydroxyl groups, when absent, are often mimicked by ordered water molecules not only at the primary combining site, but also at the site of the second sugar ring. The similarity of peanut-lectin-sugar interactions with those in other galactose/N-acetylgalactosamine-specific lectins also extend to a substantial degree to water bridges. The comparative study provides a structural explanation for the exclusive specificity of peanut lectin for galactose at the monosaccharide level, compared with that of the other lectins for galactose as well as N-acetylgalactosamine. The complexes also provide a qualitative structural rationale for differences in the strengths of binding of peanut lectin to different sugars.

Amino Sugars↗
PubMed1991

Antibodies to mouse laminin in patients with systemic sclerosis (scleroderma) recognize galactosyl (alpha 1-3)-galactose epitopes.

Employing radioimmunoinhibition assays with distinct oligosaccharides as inhibitors, this study demonstrates that the epitope recognized on mouse laminin by sera from patients with systemic sclerosis (scleroderma) is a terminal galactosyl (alpha 1-3)-galactose disaccharide. The reaction with this alpha-digalactose was further confirmed when the sera were tested in radioimmunoassay (RIA) binding assay and in ELISA with synthetic galactose alpha 1-3 galactose coupled to human serum albumin. The circulating antibody appeared restricted to the IgG class and mostly to the subclass IgG3 and IgG4. Antibodies with the same specificity can be found in patients with American cutaneous leishmaniasis and Chagas disease; however, whilst in these diseases the antibody production is triggered by antigenic determinants present on the surface of the parasites, the events eliciting their appearance in systemic sclerosis are unknown.

Disaccharides↗
PubMed1986

Isolation and characterization of a galactose binding lectin with insulinomimetic activities. From the seeds of the bitter gourd Momordica charantia (Family Cucurbitaceae).

A galactose binding lectin was isolated from the seeds of the bitter gourd Momordica charantia by delipidation with petroleum ether, extraction with phosphate buffered saline, ammonium sulfate precipitation and affinity chromatography on lactogel. The lectin had a molecular weight of 124,000 and approximately 5% carbohydrate content. The molecular weights of the individual subunits were 37,000, 35,000 and 33,000. The lectin exhibited potent hemagglutinating activity. In addition, it demonstrated antilipolytic and lipogenic activities in isolated rat adipocytes although it did not possess intrinsic lipolytic activity. The antilipolytic activity was susceptible to destruction by heat, trypsin, chymotrypsin, glutathione and galactose, indicating that the integrity of the protein moiety, the disulfide linkages, and galactose, which is the sugar specifically bound by the lectin, all play an important role in interaction with the adipocyte leading to an expression of this insulin-like activity.

Adipose Tissue↗
PubMed1995

Structural studies of the putative O-specific polysaccharide of Acinetobacter baumannii O2 containing 3,6-dideoxy-3-N-(D-3-hydroxybutyryl)amino-D-galactose.

A polysaccharide containing D-galactose, 2-deoxy-2-N-acetylamino-D-galactose and 3,6-dideoxy-3-N-(D-3-hydroxybutyryl)amino-D-galactose, probably corresponding to the lipopolysaccharide side chain, was obtained from an aqueous phenol extract of isolated cell walls from Acinetobacter baumannii strain O2. By means of NMR studies and chemical degradations, the repeating unit of the polymer was identified as a branched hexasaccharide of the structure shown, where Fuc3N represents 3-amino-3,6-dideoxygalactose and R represents D-3-hydroxybutyryl. Serological tests indicated that the polymer corresponded to the O2 antigen.

Acinetobacter↗
PubMed1997

Structural studies of the O-antigenic polysaccharide of the lipopolysaccharide from Acinetobacter (DNA group 11) strain 94 containing 3-amino-3,6-dideoxy-D-galactose substituted by the previously unknown amide-linked L-2-acetoxypropionic acid or L-2-hydroxypropionic acid.

A polysaccharide containing D-Gal, D-GalNAc, 3-(L-2-acetoxypropionamido)-3,6-dideoxy-D-galactose (approximately 80%) and 3-(L-2-hydroxypropionamido)-3,6-dideoxy-D-galactose (approximately 20%) was isolated by mild acid hydrolysis, followed by gel-permeation chromatography, from the phenol-soluble lipopolysaccharide (phenol/water extracted) derived from Acinetobacter strain 94. The polysaccharide, characterised by means of monosaccharide analyses, partial acid hydrolysis, and NMR studies, consisted of a branched tetrasaccharide repeating unit, as depicted below, in which Fucp3Nacyl represents 3-(L-2-hydroxypropionamido)-3,6-dideoxy-D-galactose, in which approximately 80% of the acyl residues are O-acetylated. These Fucp3N derivatives and an O-acetylated acyl group are therefore constituents of bacterial LPS, but to our knowledge are not present in any other natural carbohydrates. [sturcture: see text]

Acinetobacter↗
PubMed1976

Utilization of Lactose, Glucose, and Galactose by a Mixed Culture of Streptococcus thermophilus and Lactobacillus bulgaricus in Milk Treated with Lactase Enzyme.

The mechanism responsible for an increased rate of acid production when yogurt starter cultures are grown in milk treated with lactase enzyme was investigated by studying carbohydrate utilization and acid development by a pure culture of Streptococcus thermophilus and a mixed yogurt starter culture consisting of S. thermophilus and Lactobacillus bulgaricus. In milk containing glucose, galactose, and lactose, glucose and lactose (but not free galactose) were fermented. Fermentation of lactose in control milk was accompanied by the release of free galactose, with the result that carbohydrate utilization was less efficient than in treated milk. This phenomenon also occurred when lactose was fermented by S. thermophilus in broth culture. Carbohydrate utilization by the mixed yogurt culture was more rapid when the lactose in milk was partially prehydrolyzed. Our results suggest that the more rapid acid development that took place when a mixed yogurt starter culture was grown in milk containing prehydrolyzed lactose was the result of a more rapid and efficient utilization of carbohydrate by S. thermophilus when free glucose in addition to lactose was available for fermentation. The evidence presented also suggests that uptake and utilization of glucose and lactose by S. thermophilus are different in broth and milk cultures.

Journal Article↗
PubMed2000

Correlation of activities of the enzymes alpha-phosphoglucomutase, UDP-galactose 4-epimerase, and UDP-glucose pyrophosphorylase with exopolysaccharide biosynthesis by Streptococcus thermophilus LY03.

The effects of different carbohydrates or mixtures of carbohydrates as substrates on bacterial growth and exopolysaccharide (EPS) production were studied for the yoghurt starter culture Streptococcus thermophilus LY03. This strain produces two heteropolysaccharides with the same monomeric composition (galactose and glucose in the ratio 4:1) but with different molecular masses. Lactose and glucose were fermented by S. thermophilus LY03 only when they were used as sole energy and carbohydrate sources. Fructose was also fermented when it was applied in combination with lactose or glucose. Both the amount of EPS produced and the carbohydrate source consumption rates were clearly influenced by the type of energy and carbohydrate source used, while the EPS monomeric composition remained constant (galactose-glucose, 4:1) under all circumstances. A combination of lactose and glucose resulted in the largest amounts of EPS. Measurements of the activities of enzymes involved in EPS biosynthesis, and of those involved in sugar nucleotide biosynthesis and the Embden-Meyerhof-Parnas pathway, demonstrated that the levels of activity of alpha-phosphoglucomutase, UDP-galactose 4-epimerase, and UDP-glucose pyrophosphorylase are highly correlated with the amount of EPS produced. Furthermore, a weaker relationship or no relationship between the amounts of EPS and the enzymes involved in either the rhamnose nucleotide synthetic branch of the EPS biosynthesis or the pathway leading to glycolysis was observed for S. thermophilus LY03.

Carbohydrate Metabolism↗
PubMed1988

Regulation of the galactose-inducible lac operon and the histidine utilization operons in pts mutants of Klebsiella aerogenes.

Galactose appears to be the physiological inducer of the chromosomal lac operon in Klebsiella aerogenes. Both lactose and galactose are poor inducers in strains having a functional galactose catabolism (gal) operon, but both are excellent inducers in gal mutants. Thus the slow growth of K. aerogenes on lactose reflects the rapid degradation of the inducer. Several pts mutations were characterized and shown to affect both inducer exclusion and permanent catabolite repression. The beta-galactosidase of pts mutants cannot be induced at all by lactose, and pts mutants appear to have a permanent and constitutive inducer exclusion phenotype. In addition, pts mutants show a reduced rate of glucose metabolism, leading to slower growth on glucose and a reduced degree of glucose-mediated permanent catabolite repression. The crr-type pseudorevertants of pts mutations relieve the constitutive inducer exclusion for lac but do not restore the full level of glucose-mediated permanent catabolite repression and only slightly weaken the glucose-mediated inducer exclusion. Except for weakening the glucose-mediated permanent catabolite repression, pts and crr mutations have no effect on expression of the histidine utilization (hut) operons.

Ammonia-Lyases↗
PubMed1990

Kinetics and balance of glucose and galactose appearance in the portal blood after intake of lactose or hydrolysed lactose in conscious pigs.

Five pigs (mean body weight: 66.2 kg) were fitted with portal and arterial catheters and an electromagnetic flow probe around the portal vein. One week after the surgical operation, each animal was successively fed, at 3-day intervals, with two experimental meals containing 392 g dry matter either from hydrolysed or non-hydrolysed lactose together with a protein-mineral-vitamin mixture (200 g). Portal and arterial blood concentrations of glucose, galactose and amino nitrogen were measured together with the portal blood flow rate during a postprandial period of 8 h after the intake of these experimental meals. Amounts of hexoses appearing in the portal blood after hydrolysed-lactose intake were 3- and 2-fold larger within 2 and 8 h, respectively, than after non-hydrolysed-lactose intake. Thus, enzymatic hydrolysis in the intestine is the limiting factor of lactose digestion in unadapted pigs. Whatever the type of lactose ingested, glucose appeared more rapidly and in larger amounts in the portal blood than galactose. After hydrolysed-lactose intake, the amount of glucose appearing in the portal blood exceeded the amount ingested already after 5 h. This means that a fraction of galactose was transformed into glucose during the transport by the enterocyte.

Animals↗
PubMed1969

Galactose-1-phosphate uridyltransferase and galactokinase activity in cultured human diploid fibroblasts and peripheral blood leukocytes. I. Analysis of transferase genotypes by the ratio of the activities of the two enzymes.

The specific activities of galactokinase and galactose-1-phosphate uridyltransferase were determined in peripheral blood leukocytes directly after separation from whole blood, and in cultured skin fibroblasts at various times during the subculture growth period. Growth curves were obtained for fibroblasts based on three different parameters: direct cell counts, total protein, and total deoxyribonucleic acid (DNA) content. At the time in culture when the specific activity of both enzymes was maximal and least variable, the ratio of transferase to galactokinase correlated well with the transferase genotypes of the original tissue donors. Leukocyte transferase: galactokinase ratios gave a similar distribution pattern. Whereas transferase activity in both fibroblasts and leukocytes was similar, galactokinase was approximately three times as active in fibroblasts as in leukocytes. All fibrobast cell strains tested had similar galactokinase activity regardless of transferase genotype.The kinetic properties of fibroblast galactokinase were examined. Galactose-1-phosphate inhibits galactokinase activity in both normal and galactosemic cell strains, whereas other glycolytic intermediates have no effect. There was no detectable transferase activity in eight galactosemic (Gt(G)/Gt(G)) cell strains when transferase activity was maximal in cell strains of other transferase genotypes. Inhibitors responsible for the absence of transferase activity could not be demonstrated. In addition, transferase activity in galactosemic cell lysates was not observed in cells during logarithmic growth; measurable uridine diphosphate galactose (UDPgal) pyrophosphorylase activity was found in human diploid fibroblast cultures, as well as significant levels of endogenous uridine triphosphate (UTP) in lysates of fibroblast cultures.

Black People↗
PubMed1986

A modified method for the estimation of galactose-1-phosphate.

The measurement of galactose-1-phosphate has been advocated for monitoring galactosaemia. A radioenzymatic method is described in which red-cell haemolysates are incubated with radiolabelled uridine diphospho-glucose and exogenous galactose-1-phosphate uridyl transferase. Labelled glucose-1-phosphate is formed in proportion to the amount of galactose-1-phosphate present and is separated from the labelled uridine diphospho-glucose by affinity chromatography. The method is reproducible and has a low limit of detection. This allows it to be carried out on 100 microL of packed red cells.

Boronic Acids↗
PubMed1980

A new variant of galactosemia: galactose-1-phosphate uridylytransferase sensitive to product inhibition by glucose 1-phosphate.

In the erythrocytes of a patient with the clinical symptoms of galactosemia, a galactose-1-phosphate uridylyltransferase with abnormal kinetics was observed. Under standard assay conditions, the uridylyltransferase activity was almost normal initially and became completely inactivated within 30 min. The abnormal kinetics could be ascribed to a product inhibition by glucose 1-phosphate. The inhibition was produced by a variety of sugar phosphates, the most potent of which proved to be glucose 1-phosphate, mannose 1-phosphate, and fructose 6-phosphate. The variant galactose-1-phosphate uridylyltransferase was further characterized by a lowered affinity towards galactose 1-phosphate, non-Michaelis-Menten kinetics towards UDP-glucose, an increased thermal stability, and complete inactivity upon Cellogel electrophoresis.

Child, Preschool↗
PubMed1984

Evidence that desialylation and uptake by hepatic receptors for galactose-terminated glycoproteins are immaterial to the metabolism of human choriogonadotropin in the rat.

It is widely known that removal of sialic acid from the carbohydrate chains of glycoproteins in vitro drastically reduces their survival time in the circulation; however, it is not known whether desialylation plays a significant role in the metabolism of sialylated serum glycoproteins in vivo. We have studied the metabolism of hCG and desialylated hCG (as-hCG) in rat serum and liver in vivo to assess this putative metabolic pathway for glycoprotein hormones. A single injection of as-hCG into rats was followed by its rapid removal from the circulation, principally by the liver, and its degradation into fragments of the hCG beta-subunit that lacked the carboxy-terminal peptide antigenic determinant. Continuous infusion of desialylated fetuin (as-fetuin) at a high rate along with as-hCG dramatically reduced accumulation of the beta-subunit fragments in liver and resulted in increased serum levels of as-hCG. Consequently, the MCR of as-hCG was reduced from 301 +/- 10.3 ml/h (mean +/- SE) to 13.4 +/- 1.15 ml/h by infusion of as-fetuin, which is known to compete for hepatic receptors for galactose-terminated glycoproteins. In contrast, coinfusion of as-fetuin with hCG did not influence the MCR of hCG. Furthermore, there was no serum accumulation of hCG desialylated in its hCG beta carboxy-terminal portion, with or without as-fetuin, and the quantity and pattern of immunoreactive hCG products in liver homogenate were not affected by coinfusion of as-fetuin with hCG. Thus, blockade of hepatic receptors for galactose-terminated glycoproteins did not impede hCG turnover in the circulation, impair hepatic catabolism of hCG, or lead to the accumulation of desialylated products of hCG in plasma. These data indicate that in the rat, there is negligible catabolism of glycoproteins, such as hCG, by a pathway that involves peripheral desialylation and subsequent hepatic uptake via receptors for galactose-terminated glycoproteins.

Animals↗
PubMed1988

The galactose-recognizing system of rat peritoneal macrophages; identification and characterization of the receptor molecule.

Resident rat peritoneal macrophages express a galactose-recognizing system, which mediates binding and uptake of cells and glycoproteins exposing terminal galactose residues. Here we describe the identification, isolation, and characterization of the corresponding receptor molecule. Using photoaffinity labelling of adherent peritoneal macrophages with the 4-azido-6-125I-salicylic acid derivative of anti-freeze glycoprotein 8 followed by SDS-PAGE and autoradiography, we identified the receptor of these cells as a protein with an apparent molecular mass of 42 kDa. Furthermore, cell surface receptors were radioiodinated by an affinity-supported labelling technique using the conjugate of asialoorosomucoid and lactoperoxidase, followed by extraction and isolation by affinity chromatography. Finally, the native receptor was isolated and analysed. To estimate its binding activity in solutions, a suitable binding assay was developed, using the precipitation of receptor-ligand complex with polyethylene glycol to separate bound from unbound 125I-asialoorosomucoid, which was used as ligand. It is shown that the isolated receptor binds to galactose-exposing particles and distinguishes between sialidase-treated and -untreated erythrocytes, similar to peritoneal macrophages. The binding characteristics of the membrane-bound and the solubilized receptor are described in the following paper of Lee et al.

Animals↗
PubMed1980

A new mass screening method of detecting UDP-galactose-4-epimerase deficiency.

A new mass screening method for detecting UDP-galactose-4-epimerase deficiency in newborn infants was devised so as to make a useful addition to the Guthrie test. Like Beutler's method, this method enables one to perform convenient spot tests on the basis of fluorometry of NADH. The preferred procedure was determined to be as follows: To a mixture of 10 microliter of 5-10 mM UDP-galactose, 10 microliter of 26 mM NAD, 10 microliter of a 1 M tris-HCl buffer (pH 8.0) and 10 microliter of a 1/100 dilution of a 5 mg/ml UDP-glucose dehydrogenase stock solution, distilled water is added until the total volume reaches 100 microliter. Then a blood-bearing filter paper disc is added to the mixture and, the reaction mixture is incubated at 37 degrees C for 6-17 hr. The resulting test solution is spotted on a Whatman No. 1 filter paper with a capillary tube, air-dried and tested for fluorescence with an ultraviolet light detector. No cases of UDP-galactose-4-epimerase deficiency were found in the present study.

Carbohydrate Epimerases↗
PubMed1992

Purification of uridine diphosphate-galactose:glucosyl ceramide, beta 1-4 galactosyltransferase from human kidney.

A galactosyltransferase that transfers galactose from UDP-galactose to glucosylceramide was purified 440-fold to apparent homogeneity from normal human kidney "buffy coat" preparation employing detergent extraction, ultrafiltration, and Sepharose Q column chromatography. On reducing and nonreducing gels, the enzyme resolved into two bands with apparent molecular weights on the order of 60,000 and 58,000, respectively. The activity of the enzyme was also associated with these two bands following separation on polyacrylamide gels. Analytical isoelectric focusing revealed that the pI of this enzyme is approximately 4.55. Product characterization and substrate specificity studies employing chromatography, enzymatic digestion with various glycosidases, and use of a variety of glycosphingolipid substrates revealed that the major product synthesized by this enzyme was Cer1-1 beta Glc4-1Gal, and Cer1-1 beta Glc was the preferred substrate. Digestion of the 60- and 58-kDa proteins with Staphylococcus aureus (V-8) protease revealed at least six peptides having identical electrophoretic migration. This finding suggests that the two proteins may be related to each other. Western immunoblot assays revealed that the antibody against UDP-galactose:GlcCer, beta 1-4 galactosyltransferase (GalT-2) but not galactosyltransferase UDP-Gal:N-acetyl-D-glucosaminyl-glycopeptide 4-beta-D-galactosyltransferase (EC 2.4.1.38) (B-GT) immunoprecipitated (recognized) the kidney GalT-2. In contrast, antibody against B-GT did not immunoprecipitate GalT-2. Thus our data indicate that GalT-2 and B-GT are two distinct enzymes. The availability of the enzyme GalT-2 and corresponding antibody will allow functional studies in the near future.

Blotting, Western↗
PubMed1992

UDP-galactose:globotriaosylceramide alpha-galactosyltransferase activity in rat pheochromocytoma (PC12h) cells.

The activity of alpha-galactosyltransferase in cultured rat pheochromocytoma subcloned (PC12h) cells was examined using Gb3 as the acceptor for the galactose from UDP-galactose. The major reaction product was identified as gal alpha 1-3Gb3 based on its mobility on thin-layer chromatographic (TLC) plates and susceptibility to specific galactosidases. The enzyme activity in PC12h cells was the highest at pH 7.0 while the presence of Triton CF-54 (0.1%) and Mn2+ (5 mM) was required for its full activity. The apparent Km values for Gb3 and UDP-galactose were 57 and 17 microM, respectively. The enzyme activity in PC12h cells was compared with that in parent PC12 cells, in which gal alpha 1-3Gb3 is not expressed in an appreciable amount. In the enzyme reaction with exogenous Gb3, the enzyme activity in PC12h cells was about 1.5-fold higher than that in PC12 cells. In the absence of exogenous Gb3, this difference became even more pronounced; gal alpha 1-3Gb3 was generated from endogenous Gb3 at a much higher rate in PC12h cells than in PC12 cells. These findings suggest that the higher level of the alpha-galactosyltransferase activity in PC12h cells may, at least in part, be responsible for the accumulation of unique neutral glycosphingolipids having gal alpha 1-3 terminal residues in the cells.

Adrenal Gland Neoplasms↗
PubMed1990

Monoclonal antibodies directed against the galactose-binding lectin of Entamoeba histolytica enhance adherence.

The Entamoeba histolytica galactose-binding lectin is a surface glycoprotein composed of 170- and 35-kDa subunits. Inhibition of this lectin with galactose or anti-170 kDa subunit polyclonal antibody blocks amebic adherence to target cells and colonic mucin glycoproteins. We describe the properties of 10 mAb with specificity for the 170-kDa subunit. Based on competitive binding studies, six nonoverlapping antigenic determinants on the lectin were identified. The effect of the mAb on adherence of amebic trophozoites to both Chinese hamster ovary (CHO) cells and human colonic mucins was measured. Antilectin antibodies directed against epitopes 1 and 2 enhanced adherence, with the number of amebae having at least three adherent CHO cells increasing with the addition of epitope 1 mAb from 26 +/- 9 to 88 +/- 2% and the binding of colonic mucins increasing from 34 +/- 1 to 164 +/- 3 pg/10(5) amebae. Antibody-enhanced adherence remained 90 to 100% galactose inhibitable, occurred at 4 degrees C and was not Fc mediated. Univalent Fab fragments of epitope 1 mAb augmented mucin binding by 238% and CHO cell adherence by 338%. The binding of purified lectin to CHO cells was increased from 1.1 +/- 0.1 to 2.4 +/- 0.3 ng/10(3) CHO cells by mAb directed to epitope 1, demonstrating that enhanced adherence was due to direct activation of the lectin. mAb to epitope 3 bound to the lectin only upon its solubilization from the membrane and had no effect on adherence. Adherence to CHO cells and mucins was inhibited from 50 to 75% by mAb to epitopes 4 and 5; epitope 6 mAb inhibited amebic adherence to CHO cells but not mucins. The pooled sera from 10 patients with amebic liver abscess blocked the binding to the 170-kDa subunit of mAb directed to all six epitopes. Striking individual variations in the effects of immune sera on adherence were observed. Although the sera of all 44 South African patients with amebic liver abscess had high titer anti-lectin antibodies, 16 patients' sera significantly (more than 3 SEM) enhanced adherence whereas 25 patients' sera significantly inhibited adherence. Antilectin antibodies exert profound functional effects on the interaction of E. histolytica with target cells and human colonic mucins. Exploration of the clinical consequences of adherence-enhancing and inhibitory antibody responses may give insight into the role of antilectin antibodies in immunity to invasive amebiasis.

Amebiasis↗