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PubMed1978

Galactose-6-sulfatase from Actinobacillus sp. IFO-13310 and its action on sulfated oligosaccharides from keratan sulfate.

A 6-sulfatase specific for sugasr of the galactose configuration was purified 81-fold from the crude extract of Actinobacillus sp. IFO-13310. This preparation contained activity towards both N-acetylgalactosamine 6-sulfate and galactose 6-sulfate (relative activity, 2.4 : 1). The enzyme also release inorganic sulfate from the non-reducing galactose 6-sulfate end group of a trisaccharide disulfate prepared from keratan sulfate by sequential degradation with endo-beta-galactosidase, N-acetylglucosamine-6-sulfatase and exo-beta-N-acetylglucosaminidase. In addition, a tetrasaccharide trisulfate bearing the non-reducing N-acetylglucosamine 6-sulfate end group, also enzymatically prepared from keratan sulfate, was degraded to give rise to inorganic sulfate, N-acetylglucosamine and galactose by the sequential action of this enzyme, N-acetylglucosamine-6-sulfatase, exo-beta-N-acetylglucosaminidase and exo-beta-galactosidase (Charonia lampas).

Acetylgalactosamine↗
PubMed1993

Chemical synthesis and kinetic characterization of UDP-2-deoxy-D-lyxo-hexose("UDP-2-deoxy-D-galactose"), a donor-substrate for beta-(1-->4)-D-galactosyltransferase.

Bovine beta-(1-->4)-galactosyltransferase (GalT) transfers galactose from UDP-galactose to beta-D-GlcpNAc-terminating oligosaccharides to produce N-acetyllactosamine sequences. We report here the chemical synthesis, structural characterization and enzymatic evaluation of the very labile UDP-2-deoxy-D-lyxo-hexose ("UDP-2-deoxy-galactose," 2) as an alternate donor for GalT. Donor 2 had kinetic parameters, including a Km value of 51 microM, almost identical to those for the natural substrate UDP-galactose when beta-D-GlcpNAc-O(CH2)8COOMe was used as the acceptor. The product of the enzymatic transfer was isolated and confirmed to have the expected 2'-deoxy-N-acetyllactosamine sequence.

Animals↗
PubMed1994

The sugar-combining area of the galactose-specific toxic lectin of mistletoe extends beyond the terminal sugar residue: comparison with a homologous toxic lectin, ricin.

Viscumin (the major lectin of mistletoe extract), also known as ML-1, and ricin (RCA II) belong to a group of heterodimeric toxic lectins composed of an A chain, which inhibits protein synthesis, and a B chain, which mediates entry into the cell in a galactose-specific manner. Although most of the binding force for the association of viscumin with galactose-containing ligands is generated by the nonreducing terminal galactose residue, a particular hydroxyl group on the penultimate sugar also appears to participate in the binding, suggesting that viscumin has an extended combining site. In this paper, we give further examples of affinity enhancement by the hydroxyl group situated on the penultimate sugar next to the glycosidic linkage of the terminal galactose. The structure with highest affinity for viscumin thus far discovered is beta-D-Gal-(1-->2)-beta-D-Gal. In contrast to viscumin, ricin does not have this extended binding area, as none of the disaccharides tested exhibited significant affinity enhancement.

Carbohydrate Conformation↗
PubMed1995

Mono-, di- and tri-antennary D-galactose ligands as competitive inhibitors and photoaffinity labels of the hexose transporting system in erythrocytes. A model for the irreversible blocking of receptors in cell membranes.

Starting from pentaerythritol, photolabile mono-, di-, and tri-dentate galactose derivatives as well as their 3H-labelled isotopomers were synthesised. The hydrophilic chains linking the 6 position of D-galactose to pentaerythritol consist of 13 atoms in line. The mono-, di- and tri-dentate compounds, although themselves not transported, inhibit in increasing order 14C-D-galactose transport into erythrocytes. On irradiating whole cells in the presence of ligand with 350-nm UV light, these compounds also in increasing order, could irreversibly block the hexose transport system. Irradiation without ligand has no effect. By using the 3H-labelled tridentate galactose compound the hexose transporter (zone 4.5) is specifically radiolabelled, as could be shown in an SDS-PAGE of membrane proteins from erythrocytes previously photoaffinity labelled. Radiolabelling is significantly suppressed in the presence of D-glucose.

Affinity Labels↗
PubMed1976

Biokinetics of galactose in the homozygotes and heterozygotes of both forms of galactosemia.

41 heterozygoes and 4 homozygotes with a deficiency of galactose 1-phosphate uridyl transferase and also 3 heterozygotes and 1 homozygous patient with galactokinase deficiency were subjected to intravenous galactose loading tests with a dose of 350 mg/kg body weight in order to answer the question whether it is possible to detect the heterozygotes of both types of galactosemia by this method. For comparison, 38 healthy children and adolescents, 24 children with epidemic hepatitis and 4 children with cirrhosis of the liver, which was verified by histology, were included in the study. The elimination half-life (and also the other pharmacokinetic parameters as inaugurated by Dost) was the same for all the heterozygotes for both types of galactosemia almost without exception, and for the healthy cs, children in the acute stages of hepatitis and patients with cirrhosis of the liver was prolonged 2 to 5 times the normal. In patients with hepatitis, however, the elimination half-life was normal before the transaminases. Accordingly, the galactose clearance was decreased to half and one-fourth of the normal. Hence, heterozygotes with galactosemia cannot be detected with galactose loading tests.

Adolescent↗
PubMed1988

The Philadelphia variant of galactokinase: impaired [1-14C]galactose oxidation by intact erythrocytes.

Probands with the Philadelphia variant of galactokinase (GALKP) are black people who exhibit reduced galactokinase (GALK) activity in their red blood cells (RBC), but normal activity in their white blood cells (WBC). This reduced RBC GALK was demonstrated in disrupted erythrocytes. To investigate the possibility of a missing cofactor in hemolysates from individuals with GALKP phenotype, we compared [1-14C]galactose oxidation by intact erythrocytes, with the direct GALK assay in disrupted erythrocytes. The rate of [1-14C]glucose oxidation was also measured in order to differentiate an impaired galactose metabolism from a defect further along the pentose phosphate pathway. A good correlation (p less than 0.001) was found between the direct GALK assay and [1-14C]galactose oxidation in control subjects, which indicates that this method can be used effectively for the detection of GALK defects. This was further supported by studies on samples from heterozygotes and homozygotes for the GALKG deficient gene. For all the probands with a GALKP phenotype, diminished CO2 production from galactose was observed in the absence of impaired glucose metabolism. This allowed us to confirm the existence of a GALK deficiency in intact erythrocytes due to the GALKP variant. Further studies of RBC GALK catalytic properties are needed to investigate the molecular basis of this GALK deficiency.

Blood Glucose↗
PubMed1995

Radiochemical assay of minute quantities of galactose-1-phosphate uridyltransferase activity in erythrocytes and leukocytes of galactosemia patients.

A sensitive radioisotopic method has been developed which can detect galactose-1-phosphate uridyltransferase (GALT) activity as low as 0.1% of normal control values in both erythrocytes and leukocytes. This assay utilizes carbon-14 labeled galactose-1-phosphate with high specific activity and requires removal of endogenous galactose-1-phosphate (Gal-1-P) and uridine diphosphate glucose (UDPGlc) through dialysis. Optimal exogenous UDPGlc concentration has been determined with a fixed concentration of Gal-1-P in the incubation. The rate of product, uridine diphosphate galactose (UDPGal), formation is monitored at three different times. Among 423 patients with galactosemia studied by this method, 363 patients exhibited no detectable GALT activity in their erythrocytes and 60 patients were found to have detectable erythrocyte GALT activity ranging from 0.02 to 5.0 units normal values: > 20 units). The former group of patients was designated as classic galactosemia (GG) and the latter group as galactosemia variant (GV). Leucocytes from ten patients belonging to the GG group also showed complete absence of GALT activity while leukocytes from two patients belonging to the GV group showed GALT activity at levels comparable with those found in their erythrocytes. Because there is extensive biochemical heterogeneity among galactosemia patients, we recommend that an assay with increase sensitivity be carried out on blood samples from galactosemia patients so that clinical, biochemical and molecular correlations made by different groups of investigators can be compared.

Carbon Radioisotopes↗
PubMed1988

Contact-dependent regulation of growth of diploid human fibroblasts is dependent upon the presence of terminal galactose residues on plasma membrane glycoproteins.

The growth of diploid human fibroblasts has previously been shown to be regulated mainly by the extent of cell-cell contacts [R. J. Wieser and F. Oesch (1986) J. Cell Biol. 103, 361], these contacts being effective only when terminal, beta-glycosidically linked galactose residues were present on plasma membrane glycoproteins. These studies, in which a high cell density in sparse cell cultures has been mimicked by the addition of immobilized plasma membrane glycoproteins, have been further extended to investigate the role of terminal galactose residues directly in cell cultures. The studies presented herein show that (i) culturing human fibroblasts in the presence of beta-galactosidase resulted in an approximately twofold higher saturation density, as well as a twofold higher proliferation rate at high cell densities when compared to the rates found in control cultures. (ii) The presence of alpha-lactalbumin in the culture medium, which acts as a modifier of the activity of galactosyltransferase, had the same effect as beta-galactosidase. (iii) Addition of the lectin I from Bandeiraea simplicifolia (BS I), which is specific for terminal galactose residues, resulted in an increase in the proliferation rate of cell cultures at high cell densities, while the proliferation was not affected at low cell densities. These data show that the presence of terminal, beta-glycosidically linked galactose is vital for the efficient growth control of normal cells.

Cells, Cultured↗
PubMed1985

Acid phosphatase II. Cytochemical localization in lenses of normal and galactose-fed rats.

Previous cytochemical and biochemical studies have shown an increase in the activity of acid phosphatase and arylsulfatase during the induction of galactose cataracts in rat lenses. It was postulated that these enzymes may be involved in lens fiber degradation observed during cataractogenesis, however, the role of these enzymes in the repair process was not ruled out. The present investigation has evaluated the level of acid phosphatase activity in lenses in which the induction of opacity is inhibited with the aldose reductase inhibitor sorbinil and during the recovery of galactose induced opacity. Sprague-Dawley rats received 50% galactose diet, or galactose diet with sorbinil, or laboratory chow diet. Following 20 days on this diet all rats received lab chow plus 50 mg kg-1 sorbinil (recovery diet). The lenses were removed at desired intervals following the initiation of the above three diets and following the transfer of animals to the recovery diet. Cytochemical localization and biochemical quantitation of acid phosphatase activity were performed with methods previously reported. Most of the enzyme activity was localized within the epithelial cells and superficial cortical fibers. In the epithelial cell layer, the enzyme activity was primarily localized in lysosomes and at extracellular sites near the epithelial cell membrane which abut each other and cortical fibers. In cortical fibers the enzyme activity was observed at various extracellular sites between the cell membranes of neighboring fibers. The effect of sorbinil, if any, and the possible role of acid hydrolases in the repair process during cataract reversal is discussed.

Acid Phosphatase↗
PubMed1993

Synthesis of 2-deoxy-D-galactose containing gangliosides in vivo.

Incorporation of 2-deoxy-D-galactose into the oligosaccharide moieties of different gangliosides of rat liver was examined. After intraperitoneal administration of 2-deoxy-D-galactose it was shown by GLC/MS analysis that this hexose analogue is metabolized and incorporated into all the gangliosides investigated, and predominantly into GM3 and GD3. In both of these gangliosides, 25-55% of the galactose residues were substituted by 2-deoxy-D-galactose. The epimer, 2-deoxy-D-glucose, was not detectable.

Animals↗
PubMed1983

The sialic acid and galactose concentrations in erythrocyte membranes in patients with myotonic dystrophy, limb-girdle and facioscapulohumeral dystrophy.

Sialic acid is an important constituent of membrane-bound glycoproteins and glycolipids. It occurs linked to galactose at the surface of the membrane and is involved in, e.g., cation exchange, receptor function, maintenance of membrane polarity and intercellular interactions. In myotonic dystrophy there is evidence of an as yet basically undefined plasma-membrane abnormality. Considering the importance of sialic acid in membrane function, sialic acid as well as galactose concentrations were measured in erythrocyte membranes from 17 patients with myotonic dystrophy and compared to 17 matched healthy controls. There was a highly significant (P less than 0.0005) reduction of the sialic acid concentration in the patients, while no significant difference in galactose concentration was found. In 16 patients with limb-girdle and facioscapulohumeral dystrophy, sialic acid and galactose concentrations did not differ from matched controls. The possible importance of a reduced concentration of membrane-bound sialic acid in myotonic dystrophy is discussed in relation to previously reported biochemical membrane abnormalities in this disease.

Adult↗
PubMed1991

Nerve conduction velocity and axonal transport of 6-phosphofructokinase activity in galactose-fed rats.

This study examined sciatic motor nerve conduction velocity (MNCV) and the accumulation of 6-phosphofructokinase (PFK) activity proximal and distal to a sciatic nerve ligature in rats fed a diet containing 20% galactose for 4 weeks. MNCV was reduced in the galactose-fed rats to 94% of controls, (P less than 0.05) but PFK activity accumulations were not different from those in controls. Daily administration of the aldose reductase inhibitor ponalrestat throughout the study to another group of galactose-fed rats prevented dulcitol accumulation, myo-inositol depletion and increased water content of the sciatic nerve seen in galactose-fed rats. This effective aldose reductase inhibition also prevented the reduced MNCV and had no effect on accumulations of PFK activity. These data support earlier work suggesting that deficits in the axonal transport of PFK activity in diabetic rats are unrelated to either exaggerated flux through the polyol pathway, polyol accumulation or ischemic hypoxia and indicate the possible need for the elucidation of other pathogenic mechanisms which may contribute to the development of diabetic neuropathy.

Aldehyde Reductase↗
PubMed1990

In vivo metabolism and UTP-depleting action of 2-deoxy-2-fluoro-D-galactose.

The metabolism of 2-deoxy-2-fluoro-D-galactose (dGalF) was studied in rodents using HPLC, enzymatic methods, and 19F-NMR spectroscopy in vivo and in vitro. The liver took up the major part of the administered dose of the 14C-labeled D-galactose analog. This was confirmed in vivo by use of the 18F-labeled sugar (1.5 mCi/kg; 25 mumol/kg) and examination by positron emission tomography. After a dose of 1 mmol/kg, dGalF-1-phosphate accumulated rapidly (5.3 +/- 0.4 mmol/kg after 30 min), followed by formation of UDP-dGalF and UDP-2-deoxy-2-fluoro-D-glucose (0.7 +/- 0.1 and 1.8 +/- 0.1 mmol/kg, respectively, after 5 hr). Good quantitative agreement was obtained between the measurements by HPLC and enzymatic analyses and by 19F-NMR. The noninvasive in vivo 19F-NMR technique is particularly advantageous, since it allows the simultaneous analysis of all dGalF metabolites. The diversion of uridylate, due to the accumulation of UDP-2-deoxy-2-fluoro-D-hexoses, was associated with a rapid depletion of hepatic UTP, UDP-glucose, and UDP-galactose. The UTP content was decreased to 11 +/- 6% of normal within 15 min after administration of dGalF at a dose of 1 mmol/kg. The UTP-depleting action was minimal, however, at a dose of 25 mumol/kg or less, indicating that interference in uridylate metabolism will be negligible at the doses required for positron emission tomography of the liver using the 18F-labeled compound. At higher doses the UTP deficiency induced by dGalF may be useful in the chemotherapy of D-galactose-metabolizing tumors such as hepatocellular carcinoma. At moderate doses of dGalF, 19F-NMR spectroscopy in vivo or in vitro could be used to pinpoint defects of the enzymes that cause galactosemia, i.e. of galactokinase, uridyltransferase, or 4-epimerase.

Animals↗
PubMed1981

Studies on the galactose-binding site of ricin and the hybrid toxin Man6P-ricin.

N-acetylimidazole (NAI) was used to O-acetylate the plant seed toxin ricin. O-acetylation of one to two tyrosine residues per molecule of ricin inhibited ricin binding to Sepharose 4B and decreased toxicity by 90% in a protein synthesis inhibition assay in HeLa cells. Lactose, known to block the binding site on the ricin B subunit, protected ricin from NAI modification of binding or toxicity. Thus NAI, under these conditions, can be a lactose site-specific inhibitor. The lactose site-specific modification of the hybrid toxin, Man6P-ricin, performed under the same conditions, exhibited the same 90% inhibition of Man6P receptor-mediated toxicity as the galactose-containing receptor-mediated toxicity of either Man6P-ricin or ricin. Thus the ricin B chain lactose-binding site appears to be essential for the high potency of Man6P-ricin via the new cell type-specific Man6P receptor. Treatment of fibroblasts with neuraminidase exposes galactose residues, thus increasing the sensitivity to ricin eight fold. The Man6P receptor-mediated toxicity of Man6P-ricin is not affected by this treatment, although the galactose-inhibited route is potentiated eight fold. The Man6P-ricin hybrid appears to require the ricin B chain galactose-binding site to enter the cytosol after initially binding to the Man6P receptor. These data provide some insights into the proper design of hybrid toxins. We discuss a number of possible models for hybrid toxin entry.

Acetylation↗
PubMed1982

Uptake of galactose by the epithelial syncytium of Schistosoma mansoni.

A steady-state compartmental analytical solution to radiolabeled galactose fluxes into and out of S. mansoni using a three compartment model is presented. Experiments included phlorizin inhibition, Na+-free incubations and inhibition experiments with glucose and 3-O-methylglucose. The inward rate constants exceeded the outward exchange rates by a factor of 1.55 in females and 1.85 in males. Phlorizin, Na+-free conditions and the other hexoses reduced the inward exchange rates such that net secretion of galactose would be favored since the inward to outward exchange rates were less than unity. In the Na+-free incubations, the outward exchange rate was increased but not in the other experiments. The steady-state Kt values were increased in Na+-free incubations and during inhibitions by glucose and 3-O-methylglucose, but not in response to phlorizin. The size of the exchangeable tissue pool of galactose was decreased in a predictable manner when the exchange rates across the surface epithelial syncytium were reduced by glucose, 3-O-methylglucose, phlorizin and Na+-free incubations. The results were generally consistent with previous findings of stereospecific Na+-coupled uptake of galactose by S. mansoni.

3-O-Methylglucose↗
PubMed1975

Affinity chromatography of galactose containing biopolymers using covalently coupled Ricinus communis lectin to Sepharose 4B.

A galactose-specific lectin isolated from Ricinus communis beans has been covalently coupled to Sepharose 4B activated with cyanogen bromide. The immobilized lectin retains its polysaccharide-binding property. The Sepharose-lectin can be used for the purification of polysaccharides containing terminal nonreducing galactose. Only a small fraction of 'native fetuin' and 'native ceruloplasmin' are retarded on Sepharose-lectin. On analysis it was observed that they had a lower content of sialic acids as compared to the native and unbound glycoproteins (sialated fractions). However, on desialation, fetuin and ceruloplasmin were completely adsorbed to Sepharose-lectin. The asialoglycoproteins interact strongly with Sepharose-lectin as compared to 'partially sialated glycoproteins'. This has been attributed to the exposure of galactose residues of these glycoproteins on enzymatic desialation. These experiments demonstrated that Sepharose-lectin interacts with glycoproteins through their terminal, non-reducing galactose. On the basis of these experiments it is suggested that Sepharose-lectin can be used as an analytical tool for separation of 'fully sialated glycoproteins' from the 'partially sialated glycoproteins'.

Ceruloplasmin↗
PubMed1977

Incorporation of galactose into galactosyltransferase.

Bovine skim milk galactosyltransferase (EC 2.4.1.22) retained its catalytic activity after partial enzymatic removal of sialic acid and galactose. Desialylated and degalactosylated galactosyltransferase was a galactosyl acceptor in the galactosyltransferase reaction. [14C]Galactose from UDP-[14C]galactose was incorporated into the carbohydrate-depleted galactosyltransferase by native galactosyltransferase. The results suggest that galactosyltransferase participates in the biosynthesis of its glycopeptides of the sialic acid-galactose-N-acetylglucosamine type.

Animals↗
PubMedDate not supplied

Effect of chronic ethanol on D-galactose absorption by the rat whole intestinal surface.

The in vivo absorption of D-galactose by rat whole intestinal surface after 4 weeks of 30% ethanol ingestion in drinking water has been studied, and the results were compared with ad lib-fed control rats. The total serosal intestinal area was determined by integration obtaining similar values between control and alcohol-treated groups. In the caecum surface of ethanol-fed rats slight but not significant increases were found, while the jejunum area decreased with respect to control rats. Total galactose absorption during 10 min of perfusion was slightly increased in ethanol-fed rats but these results were not significant with the substrate concentrations tested. When absorption data were referred to serosal surface, the absorption/cm2 values in ethanol-fed rats were increased at the studied galactose concentrations although these results were only statistically significant at 10 mM. In conclusion, the present data indicates a slight increase in D-galactose absorptive capacity by the whole intestine in ethanol-fed rats which suggest that the tissue traditionally not evaluated such as caecum and colon could modify the functional response to the absorption nutrients.

Animals↗