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PubMed2001

Structural studies on fucoidans from the brown seaweed Sargassum stenophyllum.

The brown seaweed Sargassum stenophyllum biosynthesizes two different sets of fucoidans. One of them is characterized by higher percentages of glucuronic acid and fewer sulfate groups, which are situated on different sugar units. alpha-L-Fucose was the major component but other sugars like beta-D-galactose, beta-D-mannose, alpha-D-glucuronic acid, alpha-D-glucose and beta-D-xylose were also in substantial amounts. Fucoidans from the other set contain small amounts of alpha-D-glucuronic acid and high percentages of sulfate groups, which are concentrated on the fucose residues, with only fucose and galactose as major components. Structural studies of one fucoidan from each set suggest that these products have a general basic structure that has a formal resemblance to that of the fucosylated chondroitin sulfates from the body wall of sea cucumbers, namely, a linear core (formed mainly by (1-->6)-beta-D-galactose and/or (1-->2)-beta-D-mannose units) with branched chains of 'fucans' (formed by (1-->3) and/or (1-->4)-alpha-L-fucose, (1-->4)-alpha-D-glucuronic acid, terminal beta-D-xylose and, sometimes, (1-->4)-alpha-D-glucose). In fucoidans from the second set, the 'core' is reduced to short galactan chains.

Anticoagulants↗
PubMedDate not supplied

Modulation of pharmacokinetics of radioiodinated sugar-conjugated somatostatin analogues by variation of peptide net charge and carbohydration chemistry.

Sugar conjugation of biooactive peptides has been shown to be a powerful tool to modulate peptide pharmacokinetics. In the case of radiolabeled somatostatin analogues developed for in vivo scintigraphy of somatostatin receptor (sst) expressing tumors, it generally led to tracers with predominant renal excretion and low uptake in nontarget organs, and in some cases also with enhanced tumor accumulation. Especially with respect to endoradiotherapeutic applicability of these tracers, however, understanding the structural requirements for minimal kidney accumulation and maximal tumor uptake is important. The aim of this study was therefore the evaluation of the potential of specific glycoside structures in combination with reduced peptide net charge to reduce kidney accumulation without affecting tumor accumulation. Three glyco analogues of radioiodinated Tyr(3)-octreotate (TOCA) with z = 0 were evaluated in a comparative study using [(125)I]Mtr-TOCA (z = +1), the maltotriose-Amadori analogue of [(125)I]TOCA, as a reference, [(125)I]Glucuron-TOCA, the Amadori conjugate with glucuronic acid, and [(125)I]Gluc-S- and [(125)I]Gal-S-TOCA, the coupling products with glucosyl- and mannosyl-mercaptopropionate. In cells transfected with sst(1)-sst(5), all three new analogues show sst-subtype binding profiles similar to I-Mtr-TOCA with high, but somewhat reduced, affinity for sst(2). In contrast, internalization into sst(2)-expressing cells (in % of [(125)I]Tyr(3)-octreotide ([(125)I]TOC)) as well as the EC(50,R) of unlabeled TOC for internalization determined in dual-tracer experiments are substantially enhanced for [(123)I]Gal-S-TOCA and [(123)I]Gluc-S-TOCA (internalization, 190% +/- 12% and 265% +/- 20%, respectively, vs 168% +/- 6% of [(125)I]TOC for [(123)I]Mtr-TOCA; EC(50,R), 2.62 +/- 0.07 and 2.96 +/- 0.14, respectively, vs 1.81 +/- 0.07 for [(123)I]Mtr-TOCA). The tumor accumulation of [(125)I]Gal-S-TOCA and [(125)I]Gluc-S-TOCA in AR42J tumor-bearing nude mice 1 h p.i. is consequently very high (22.6 +/- 2.2 and 26.2 +/- 5.6%ID/g) and comparable to that of [(125)I]Mtr-TOCA (25.1 +/- 4.4%ID/g). [(125)I]Glucuron-TOCA showed lower uptake in sst-expressing tissues than did [(125)I]Mtr-TOCA, but considerably enhanced accumulation in nontarget organs such as liver, intestine, and kidney. Due to increased lipophilicity, hepatic and intestinal uptake 1 and 4 h p.i. of [(125)I]Gal-S-TOCA and [(125)I]Gluc-S-TOCA was also slightly higher than that of [(125)I]Mtr-TOCA. Kidney accumulation, however, was reduced by approximately 50% for both compounds (2.6 +/- 0.3 and 2.2 +/- 0.4, respectively, vs 4.0 +/- 0.7%ID/g at 1 h p.i.). Because no sugar-specific effect was detected in the latter case, it is concluded that general ligand pharmacokinetics and especially kidney accumulation of the tracers investigated are mainly determined by physicochemical characteristics such as lipophilicity, net charge, and also charge distribution ([(125)I]Glucuron-TOCA vs [(125)I]Gal-S- and [(125)I]Gluc-S-TOCA). With respect to receptor targeting, however, the structure of the carbohydrate moiety plays an important role, leading to dramatically enhanced ligand internalization, especially in the case of [(123)I]Gluc-S-TOCA. Taking into account the combined effects of the Gluc-S-moiety both on kidney and on tumor accumulation, this group seems to be a promising synthon for the synthesis of other radiolabeled peptide analogues with improved pharmacokinetics.

Animals↗
PubMed2006

Tetranuclear copper(II) complexes bridged by alpha-D-glucose-1-phosphate and incorporation of sugar acids through the Cu4 core structural changes.

Tetranuclear copper(II) complexes containing alpha-D-glucose-1-phosphate (alpha-D-Glc-1P), [Cu4(mu-OH){mu-(alpha-D-Glc-1P)}2(bpy)4(H2O)2]X3 [X = NO3 (1a), Cl (1b), Br (1c)], and [Cu4(mu-OH){mu-(alpha-D-Glc-1P)}2(phen)4(H2O)2](NO3)3 (2) were prepared by reacting the copper(II) salt with Na2[alpha-D-Glc-1P] in the presence of diimine ancillary ligands, and the structure of 2 was characterized by X-ray crystallography to comprise four {Cu(phen)}2+ fragments connected by the two sugar phosphate dianions in 1,3-O,O' and 1,1-O mu4-bridging fashion as well as a mu-hydroxo anion. The crystal structure of 2 involves two chemically independent complex cations in which the C2 enantiomeric structure for the trapezoidal tetracopper(II) framework is switched according to the orientation of the alpha-D-glucopyranosyl moieties. Temperature-dependent magnetic susceptibility data of 1a indicated that antiferromagnetic spin coupling is operative between the two metal ions joined by the hydroxo bridge (J = -52 cm(-1)) while antiferromagnetic interaction through the Cu-O-Cu sugar phosphate bridges is weak (J = -13 cm(-1)). Complex 1a readily reacted with carboxylic acids to afford the tetranuclear copper(II) complexes, [Cu4{mu-(alpha-D-Glc-1P)}2(mu-CA)2(bpy)4](NO3)2 [CA = CH3COO (3), o-C6H4(COO)(COOH) (4)]. Reactions with m-phenylenediacetic acid [m-C6H4(CH2COOH)2] also gave the discrete tetracopper(II) cationic complex [Cu4{mu-(alpha-D-Glc-1P)}2(mu-m-C6H4(CH2COO)(CH2COOH))2(bpy)4](NO3)2 (5a) as well as the cluster polymer formulated as {[Cu4{mu-(alpha-D-Glc-1P)}2(mu-m-C6H4(CH2COO)2)(bpy)4](NO3)2}n (5b). The tetracopper structure of 1a is converted into a symmetrical rectangular core in complexes 3, 4, and 5b, where the hydroxo bridge is dissociated and, instead, two carboxylate anions bridge another pair of Cu(II) ions in a 1,1-O monodentate fashion. The similar reactions were applied to incorporate sugar acids onto the tetranuclear copper(II) centers. Reactions of 1a with delta-D-gluconolactone, D-glucuronic acid, or D-glucaric acid in dimethylformamide resulted in the formation of discrete tetracopper complexes with sugar acids, [Cu4{mu-(alpha-D-Glc-1P)}2(mu-SA)2(bpy)4](NO3)2 [SA = D-gluconate (6), D-glucuronate (7), D-glucarateH (8a)]. The structures of 6 and 7 were determined by X-ray crystallography to be almost identical with that of 3 with additional chelating coordination of the C-2 hydroxyl group of D-gluconate moieties (6) or the C-5 cyclic O atom of D-glucuronate units (7). Those with D-glucaric acid and D-lactobionic acid afforded chiral one-dimensional polymers, {[Cu4{mu-(alpha-D-Glc-1P)}2(mu-D-glucarate)(bpy)4](NO3)2}n (8b) and {[Cu4{mu-(alpha-D-Glc-1P)}2(mu-D-lactobionate)(bpy)4(H2O)2](NO3)3}n (9), respectively, in which the D-Glc-1P-bridged tetracopper(II) units are connected by sugar acid moieties through the C-1 and C-6 carboxylate O atoms in 8b and the C-1 carboxylate and C-6 alkoxy O atoms of the gluconate chain in 9. When complex 7 containing d-glucuronate moieties was heated in water, the mononuclear copper(II) complex with 2-dihydroxy malonate, [Cu(mu-O2CC(OH)2CO2)(bpy)] (10), and the dicopper(II) complex with oxalate, [Cu2(mu-C2O4)(bpy)2(H2O)2](NO3)2 (11), were obtained as a result of oxidative degradation of the carbohydrates through C-C bond cleavage reactions.

Carboxylic Acids↗
PubMed1970

The effect of steroids and nucleotidesoon solubilized bilirubin uridine diphosphate-glucuronyltransferase.

1. It was confirmed that bilirubin glucuronyltransferase can be obtained in solubilized form from rat liver microsomes. 2. Michaelis-Menten kinetics were not followed by the enzyme with bilirubin as substrate when the bilirubin/albumin ratio was varied. High concentrations of bilirubin were inhibitory. 3. The K(m) for UDP-glucuronic acid at the optimum bilirubin concentration was 0.46mm. 4. Low concentrations of Ca(2+) were inhibitory in the absence of Mg(2+) but stimulatory in its presence; the converse applied for EDTA. 5. UDP-N-acetylglucosamine and UDP-glucose enhanced conjugation by untreated, but not by solubilized microsomes. 6. The apparent 9.5-fold increase in activity after solubilization was probably due to the absence of UDP-glucuronic acid pyrophosphatase activity in the solubilized preparation. 7. The activation of solubilized enzyme activity by ATP was considered to be a result of chelation of inhibitory metal ions. 8. The solubilized enzyme activity was inhibited by UMP and UDP. The effect of UMP was not competitive with respect to UDP-glucuronic acid. 9. A number of steroids inhibited the solubilized enzyme activity. The competitive effects of stilboestrol, oestrone sulphate and 3beta-hydroxyandrost-5-en-17-one, with respect to UDP-glucuronic acid, may be explained on an allosteric basis.

Adenine Nucleotides↗
PubMed1981

Bovine aortic chondroitin sulphate- and dermatan sulphate-containing proteoglycans. Isolation, fractionation and chemical characterization.

1. Guanidinium chloride (4M) in the presence of proteinase inhibitors extracted 90% of bovine aorta galactosaminoglycans as proteoglycans that were subsequently purified by ion-exchange and gel chromatography. 2. Fractionation of the calcium salts of the purified proteoglycans with increasing concentration of ethanol yielded fractions PG-25 (28%), PG-35 (45%) and PG-50 (37%). 3. Fraction PG-50 contained proteochondroitin 6-sulphate, whereas fractions PG-25 and PG-35 were proteodermatan sulphates of greatly different carbohydrate composition; the molar proportions of L-iduronate-N-acetylgalactosamine 4-sulphate, D-glucuronate-N-acetyl-galactosamine 4-sulphate and D-glucuronate-N-acetylgalactosamine 6-sulphate were 75: 18 :7 in fraction PG-25 and 14 :46 :40 in fraction PG-35. 4. The presence of alternating or mixed sequences with L-iduronate- and D-glucuronate-containing repeating disaccharides was indicated by the formation of tetrasaccharides after chondroitinase AC digestion (single L-iduronate residues) and by the release of fragments containing four or five consecutive D-glucuronate-N-acetylgalactosamine repeats after periodate oxidation and alkaline elimination. 5. The amino acid compositions of fractions PG-25 and PG-35 were similar and markedly different from that of fraction PG-50, which also contained more side chains.

Amino Acids↗
PubMed2000

Matrix polysaccharide precursors in Arabidopsis cell walls are synthesized by alternate pathways with organ-specific expression patterns.

The expression pattern of the single-copy gene UDP-glucose dehydrogenase (Ugd) was analysed in transgenic Arabidopsis plants by promoter:GUS and GFP fusions, Western blots, activity assays and histochemical activity staining. The enzyme oxidizes UDP-glucose to UDP-glucuronic acid and thus directs carbohydrates irreversibly into a cell wall-specific pool of nucleotide sugars. UDP-glucuronic acid is the central intermediate in the interconversion pathway to other nucleotide sugars, including the UDP-derivatives of arabinose, xylose, apiose and galacturonic acid which account for half the biomass of a typical Arabidopsis leaf cell wall. These activated sugars are needed as substrates for the biosynthesis of matrix polysaccharide polymers. In plants up to 5 days old the Ugd gene is strongly expressed in young roots, but very little in hypocotyls. Older plants show a more uniform expression pattern with a preference for the vascular system. A complex expression pattern was observed in flowers with high activity in the stamen, stigma and nectaries. Meristems in the leaf axil of rosette and inflorescence leaves exhibit a high level of activity of the Ugd gene. Although many of the growing tissues show high activity levels of the Ugd gene, others such as the hypocotyl and the cotyledons of young seedlings do not. Instead these tissues efficiently incorporate 3H-inositol into their cell walls. This indicates the biosynthesis of UDP-glucuronic acid through an alternative pathway via the oxidation of inositol to glucuronic acid and subsequent activation to the nucleotide sugar. The data strongly suggest two alternative pathways for matrix polysaccharide precursors with spatial and developmental regulation.

Arabidopsis↗
PubMed1998

Purification of the lysosomal sialic acid transporter. Functional characteristics of a monocarboxylate transporter.

Sialic acid and glucuronic acid are monocarboxylated monosaccharides, which are normally present in sugar side chains of glycoproteins, glycolipids, and glycosaminoglycans. After degradation of these compounds in lysosomes, the free monosaccharides are released from the lysosome by a specific membrane transport system. This transport system is deficient in the human hereditary lysosomal sialic acid storage diseases (Salla disease and infantile sialic acid storage disease, OMIM 269920). The lysosomal sialic acid transporter from rat liver has now been purified to apparent homogeneity in a reconstitutively active form by a combination of hydroxyapatite, lectin, and ion exchange chromatography. A 57-kDa protein correlated with transport activity. The transporter recognized structurally different types of acidic monosaccharides, like sialic acid, glucuronic acid, and iduronic acid. Transport of glucuronic acid was inhibited by a number of aliphatic monocarboxylates (i.e. lactate, pyruvate, and valproate), substituted monocarboxylates, and several dicarboxylates. cis-Inhibition, trans-stimulation, and competitive inhibition experiments with radiolabeled glucuronic acid as well as radiolabeled L-lactate demonstrated that L-lactate is transported by the lysosomal sialic acid transporter. L-Lactate transport was proton gradient-dependent, saturable with a Km of 0.4 mM, and mediated by a single mechanism. These data show striking biochemical and structural similarities of the lysosomal sialic acid transporter with the known monocarboxylate transporters of the plasma membrane (MCT1, MCT2, MCT3, and Mev).

Animals↗
PubMed2005

Up-regulation of human myo-inositol oxygenase by hyperosmotic stress in renal proximal tubular epithelial cells.

myo-Inositol oxygenase (MIOX) catalyzes the oxidative cleavage of myo-inositol (MI) to give d-glucuronic acid, a committed step in MI catabolism. d-Glucuronic acid is further metabolized to xylitol via the glucuronate-xylulose pathway. Although accumulation of polyols such as xylitol and sorbitol is associated with MI depletion in diabetic complications, no causal relationship has been established. Therefore we are examining the role of MIOX in diabetic nephropathy. Here we present evidence that the basis for the depletion of MI in diabetes is likely to be mediated by the increased expression of MIOX, which is induced by sorbitol, mannitol, and xylitol in a porcine renal proximal tubular epithelial cell line, LLC-PK1. To understand the molecular mechanism of regulation of MIOX expression by polyols, we have cloned the human MIOX gene locus of 10 kb containing 5.6 kb of the 5' upstream sequence. Analysis of the 5' upstream sequence led to the identification of an osmotic response element (ORE) in the promoter region, which is present approximately 2 kb upstream of the translation start site. Based on luciferase reporter and electrophoretic mobility shift assays, polyols increased the ORE-dependent expression of MIOX. In addition, we demonstrate that the activity of the promoter is dependent on the binding of the transcription factor, tonicity element-binding protein, or osmotic response element-binding protein, to the ORE site. These results suggest that the expression of MIOX is up-regulated by a positive feedback mechanism where xylitol, one of the products of MI catabolism via the glucuronate-xylulose pathway, induces an overexpression of MIOX.

Animals↗
PubMed1990

Side group addition by xylosyltransferase and glucuronyltransferase in biosynthesis of capsular polysaccharide in Cryptococcus neoformans.

The capsular polysaccharide of Cryptococcus neoformans consists of an O-acetylated mannan backbone with xylosyl and glucuronyl substituents. We have studied two enzymes in the biosynthetic pathway of this polysaccharide. A particulate enzyme preparation contained xylosyltransferase and glucuronyltransferase activities with pH optima of 7.5 and less than 6.5, and optimum incubation temperatures of 25 degrees and 37 degrees C respectively. O-acetylated mannan served as an acceptor for glucuronyl residues but xylomannan did not. Glucuronomannan served as an acceptor for xylosyl residues but acetylated mannan did not. These observations suggest that glucuronate is added before xylose and after acetate. This hypothesis was supported by studies of lipid-linked sugars in which a microsomal preparation was incubated with various combinations of nucleotide sugars. With GDP-mannose, UDP-glucuronate and UDP-[14C]xylose; GDP-mannose, UDP-[14C]glucuronate and UDP-xylose; or GDP-mannose and UDP-[14C]glucuronate, no evidence for a lipid-linked monosaccharide was obtained. However, lipid-linked xylose was detected only if GDP-mannose and UDP-[14C]xylose were provided, a finding consistent with a pool of lipid-linked xylose which is only transferred following glucuronylation. The order of addition inferred is mannosyl, acetyl, glucuronyl and xylosyl.

Carbohydrate Sequence↗
PubMed1994

Patterns of uronosyl epimerization and 4-/6-O-sulphation in chondroitin/dermatan sulphate from decorin and biglycan of various bovine tissues.

Dermatan sulphate is a co-polymer of two types of disaccharide repeats: D-glucuronate-N-acetylgalactosamine and L-iduronate-N-acetylgalactosamine. The former can be O-sulphated at C-4 or C-6 of the galactosamine, whereas the latter contains almost exclusively 4-O-sulphated galactosamine. A minor proportion of the L-iduronate may be O-sulphated at C-2. Chondroitin sulphate has no L-iduronate-containing repeats. We have used our recently developed methods for sequence analysis of galactosaminoglycans to investigate the structure of dermatan/chondroitin sulphates of the proteoglycans decorin and biglycan derived from various bovine tissues, like dermis, sclera, tendon, aorta, cartilage and bone. The glycan chains, radioiodinated at the reducing end, were partially cleaved with specific enzymes (chondroitin lyases), and subjected to high-resolution polyacrylamide gel electrophoresis, blotting and autoradiography to identify fragments extending from the labelled reducing end to the point of cleavage. We used chondroitin B lyase to identify the location of L-iduronate, chondroitin AC-I lyase to locate D-glucuronate and chondroitin C lyase to cleave where D-glucuronate residues were succeeded by 6-O-sulphated N-acetylgalactosamine. We could demonstrate tissue-specific, periodic and wave-like patterns of distribution for the two epimeric uronic acids, as well as specific patterns of sulphation in dermatan sulphates derived from either decorin or biglycan. For example, some dermatan sulphates contained D-glucuronate-rich domains that were always 6-sulphated (scleral decorin), others were always 4-sulphated (decorin from bovine dermis, cartilage and bone; biglycan from aorta) or 6-sulphated near the linkage region, but 4-sulphated in more distal domains (decorin from porcine dermis and bovine tendon). Decorin from bone and articular cartilage, as well as biglycan from articular and nasal cartilage, carried largely chondroitin sulphate chains, but also some dermatan sulphate, whereas galactosaminoglycan chains derived from aggrecan of nasal cartilage were free of L-iduronate. Decorin and biglycan from the same tissue (articular cartilage or sclera) had similar glycan chains. The two side chains in a biglycan molecule are probably also similar to one another. The portion of the glycan chains nearest to the core protein was substituted with charged groups to a variable degree, which may correlate with the structural features of the main chain.

Animals↗
PubMed2004

Functional characterization of GumK, a membrane-associated beta-glucuronosyltransferase from Xanthomonas campestris required for xanthan polysaccharide synthesis.

Xanthomonas campestris is a Gram-negative bacterium that produces an exopolysaccharide known as xanthan gum. Xanthan is involved in a variety of biological functions, including pathogenesis, and is widely used in the industry as thickener and viscosifier. Although the genetics and biosynthetic process of xanthan are well documented, the enzymatic components have not been examined and no data on glycosyltransferases have been reported. We describe the functional characterization of the gumK gene product, an essential protein for xanthan synthesis. Immunoblots and complementation studies showed that GumK is a 44-kDa protein associated to the membrane fraction. This value corresponds to the expected molecular mass for GumK encoded by an extended open reading frame than proposed from previous genetic data and in X. campestris published complete genome. The protein was expressed in Escherichia coli cells. The purified protein catalyzed the transfer of a glucuronic acid residue from UDP-glucuronic acid to mannose-alpha-1,3-glucose-beta-1,4-glucose-P-P-polyisoprenyl with formation of a glucuronic acid-beta-mannose linkage. We examined the acceptor substrate specificity. GumK was unable to use the trisaccharide acceptor freed from the pyrophosphate lipid moiety. Replacement of the natural lipid moiety by phytanyl showed that the catalytic function could proceed with glucuronic acid transfer. These results suggest the enzyme does not show specificity for the lipidic portion of the acceptor. GumK showed diminished activity when tested with 6-O-acetyl-mannose-alpha-1,3-glucose-beta-1,4-glucose-P-P-polyisoprenyl, a putative intermediate in the synthesis of xanthan. This could indicate that acetylation of the internal mannose takes place after the formation of the GumK product.

Cell Membrane↗
PubMed1992

Purification and properties of 4-hydroxybiphenyl UDP-glucuronyltransferase from bovine liver microsomes.

A UDP-glucuronyltransferase isoform glucuronizes phenolic xenobiotics such as 4-nitrophenol, and an isoform glucuronizing 4-hydroxybiphenyl has also been found in rat liver. We purified a UDP-glucuronyltransferase isoform glucuronizing 4-hydroxybiphenyl from bovine liver microsomes by solubilization with 0.7% sodium cholate followed by three column chromatographic separations using DEAE-Toyopearl 650S, UDP-hexanolamine Sepharose 4B, and hydroxyapatite. The purified bovine liver 4-hydroxybiphenyl UDP-glucuronyltransferase (named Bovine 4HBGT) had glucuronidation activities toward 4-hydroxybiphenyl and 4-methylumbelliferone but had little activity toward 4-nitrophenol and 1-naphthol. The apparent molecular mass of Bovine 4HBGT was 54,000 Da on SDS-PAGE, and this was decreased to 50,000 Da by digestion with endo-beta-N-acetylglucosaminidase H. These data suggest that Bovine 4HBGT consists of a 50,000 Da polypeptide and a high mannose type oligosaccharide chain(s) of about 4,000 Da. The NH2-terminal sequence of GT-3 was GKVLVWPVDFSXWINI. These properties of Bovine 4HBGT were very similar to those of rat UDP-glucuronyltransferase glucuronizing xenobiotics. However, the NH2-terminal sequence of Bovine 4HBGT had higher homology with that of rat liver 4-hydroxybiphenyl UDP-glucuronyltransferase than with that of rat liver 4-nitrophenol UDP-glucuronyltransferase.

Amino Acid Sequence↗
PubMed1975

Metabolism of uronic acids in plant tissues: partial purification and properties of uronic Acid oxidase from citrus leaves.

A new enzyme, named uronic acid oxidase, was extracted and purified 67-fold by (NH(4))(2)SO(4) fractionation and CM-Sephadex column chromatography from ethylene-treated Shamouti orange (Citrus sinensis L. Osbeck) leaves. The enzyme catalyzes the oxidation of d-galacturonic acid and d-glucuronic acid to the corresponding hexaric acids in the presence of molecular oxygen with the production of H(2)O(2). The pH optimum for the oxidation of d-galacturonic acid and d-glucuronic acid is between 7 and 8. The enzyme is highly specific for d-galacturonic acid and d-glucuronic acid. It also oxidizes polygalacturonic acid. The apparent Michaelis constant values of the enzyme for d-galacturonic acid and d-glucuronic acid are 0.13 and 0.5 mm, respectively. The molecular weight of the enzyme, as determined by gel filtration, is about 98,000. The enzyme is inhibited by sodium hydrosulfite and other sulfites, indicating that it contains a flavin prosthetic group.

Journal Article↗
PubMed1984

Oxidation of 7-ethoxycoumarin and conjugation of umbelliferone by intact, viable epidermal cells from the hairless mouse.

Intact, viable (greater than 80%) epidermal cells were isolated from the hairless mouse. These cells metabolized 7-ethoxycoumarin (7-EC) to umbelliferone ( UMB ) (3 pmol/min/10(6) cells) and UMB to the sulfate and glucuronide conjugates (1 pmol/min/10(6) cells). The rate of oxidation in intact cells compared well with that in disrupted cells with added NADPH, but conjugation proceeded more rapidly in disrupted cells with added cofactors, due to a combination of "activation" of the UDP-glucuronosyltransferase, and to a limitation of activity by the concentration of UDP-glucuronic acid in the intact cells. Pretreatment of the animals with 5,6-benzoflavone resulted in a 5-fold increase in the rate of oxidation, and a 2-fold increase in both the rate of conjugation and the intracellular concentration of UDP-glucuronic acid. UDP-glucuronic acid concentration in isolated cells increased during incubation with glucose, and was regenerated to a steady-state concentration on incubation of cells with UMB . Pretreatment of animals with 5,6-benzoflavone decreased the percentage of metabolite conjugated (from 30% to 15%), whereas adding an inhibitor of oxidation, ellipticine, to cells isolated from pretreated animals, increased the percentage of metabolite conjugated (from 15% to 40%). Sulfation of UMB was almost undetectable, except at very low concentrations (less than 10 nM) of substrate. Thus, glucuronidation of UMB in epidermal cells may be limited by UDP-glucuronic acid availability; sulfation in the epidermis may contribute little to the conjugation of UMB ; and greater than 70% of the products of 7-EC oxidation in the skin may remain unconjugated.

Animals↗
PubMed1976

Regulation of microsomal UDP-glucuronyltransferase by metal ions. Differential effects of Mn2+ on forward and reverse reactions.

Mn2+ activates UDP-glucuronyltransferase (assayed with p-nitrophenol as aglycone) in assays of the forward reaction. The kinetic mechanism of this activation is an increase in activity at V. The rate of the reverse reaction catalyzed by UDP-glucuronyltransferase (UDP-dependent hydrolysis of p-nitrophenylglucuronic acid) is inhibited by Mn2+. The basis for this inhibition is an increase in KUDP, and a small increase in KNphGlcUA. Mn2+ appears to have no effect of the activity of the reverse reaction of saturating concentrations of both substrates. The differential effects of divalent metal ions on rates of the forward and reverse reactions catalyzed by UDP-glucuronyltransferase are due in part to differences in the affinities of UDP-glucuronic acid and UDP for metals. Keq for the formation of UDP-Mn2+ is 8.6 X 10(3); Keq for the formation of UDP-glucuronic acid-Mn2+ is 4.8 X 10(2). High concentrations of UDP thus can compete for metal ions bound to UDP-glucuronyltransferase, but UDP-glucuronic acid is less likely to do so. This competition for metal ions between the enzyme and substrates accounts for the failure of Mn2+ to increase the activity at V of the reverse reaction. Mn2+-induced inhibition of the reverse reaction, due to an increase of KUDP, reflects that the affinity of the affinity of the enzyme for UDP is greater than that for UDP-Mn2+. On the other hand, formation of a complex between UDP-glucuronic and Mn2+ does not alter the affinity of UDP-glucuronyltransferase for this nucleotide derivative

Animals↗
PubMed1991

alpha-Glucuronidase and Other Hemicellulase Activities of Fibrobacter succinogenes S85 Grown on Crystalline Cellulose or Ball-Milled Barley Straw.

Fibrobacter succinogenes produces an alpha-glucuronidase which cleaves 4-O-methyl-alpha-d-glucuronic acid from birch wood 4-O-methyl-alpha-d-glucuronoxylan. Very low levels of alpha-glucuronidase activity were detected in extracellular enzyme preparations of F. succinogenes on birch wood xylan substrate. The release of 4-O-methyl-alpha-d-glucuronic acid was enhanced when the birch wood xylan substrate was predigested by either a purified Schizophyllum commune xylanase or a cloned F. succinogenes S85 xylanase. These data suggest that the alpha-glucuronidase is unable to cleave 4-O-methyl-alpha-d-glucuronic acid from intact xylan but can act on unique low-molecular-weight glucuronoxylan fragments created by the cloned F. succinogenes xylanase. The cloned xylanase presumably must account for a small proportion of the indigenous xylanase activity of F. succinogenes cultures, since this xylanase source does not support high glucuronidase activity. The alpha-glucuronidase and associated hemicellulolytic enzymes exhibited higher activities in culture fluid from cells grown on ball-milled barley straw than in that of cellulose-grown cells. The profile of xylanases separated by isoelectric focusing (zymogram) of culture filtrate from cells grown on barley straw was more complex than that of culture filtrates from cells grown on cellulose. These data demonstrate that F. succinogenes produces an alpha-glucuronidase with an exacting substrate specificity which enables extensive cleavage of glucuronic acid residues from xylan as a consequence of synergistic xylanase action.

Journal Article↗
PubMed1993

Phagocytosis of monosaccharide-binding latex particles by guinea-pig polymorphonuclear leucocytes.

Phagocytosis of monosaccharide-binding latex particles by guinea-pig polymorphonuclear leucocytes (PMNs) was investigated. When neuraminic acid or glucuronic acid was chemically bound to the surface of latex particles the degree of phagocytosis was somewhat lower than that for bare, glucose-, mannose- or rhamnose-binding latex particles. These experimental findings were interpreted in terms of the kind of monosaccharide and the surface potential and surface hydrophobicity of latex particles. As a result, it was concluded that the inhibitory action of neuraminic acid or glucuronic acid on phagocytosis arises from an increase in the surface hydrophilicity of latex particles brought about by the hydroxyl groups and negative charges on the chemically bound neuraminic acid or glucuronic acid molecules. Physically adsorbed glucuronic acid molecules were also found to decrease the degree of phagocytosis of latex particles by PMNs, though not so remarkable as the chemically bound monosaccharide molecules.

Animals↗
PubMed1993

Identification of goat and mouse urinary metabolites of the pneumotoxin, 3-methylindole.

1. Urine from goats dosed i.v. with 3-methylindole (3MI; 15 mg/kg) or [methyl-14C] 3MI (15 mg/kg, 0.5 microCi/kg) contained at least 11 metabolites of 3MI. 2. Goat metabolized 3MI to sulfate conjugates of 4- or 7-hydroxy-3-methyloxindole, 5- or 6-hydroxy-3-methyloxindole, and 3,5- or 6-dihydroxy-3-methyloxindole; glucuronic acid conjugates of indole-3-carboxylic acid and 4- or 7-hydroxy-3-methyloxindole; and unconjugated 3-hydroxy-3-methyloxindole. Diastereoisomeric glucuronic acid conjugates of 3-hydroxy-3-methyloxindole were also identified in goat urine. 3. Urine from mice dosed i.p. with 3MI (400 mg/kg) or [ring-UL-14C] 3MI (400 mg/kg, 125 microCi/kg) contained at least six metabolites of 3MI. 4. Mice metabolized 3MI to glucuronic acid conjugates of 3,5- or 6-dihydroxy-3-methyloxindole, 5- or 6-hydroxy-3-methyloxindole, and indole-3-carboxylic acid; and unconjugated indole-3-carboxylic acid. Unconjugated 3-hydroxy-3-methyloxindole was identified in mouse urine in a previous report. 5. Both goats and mice metabolized 3MI to a mercapturate, 3-[(N-acetyl-L-cystine-S-yl)methyl]indole, which has been previously identified and was confirmed in this study. 6. 3-Methyloxindole was not identified in the urine of either goats or mice. 7. The major pathways of 3MI biotransformation in goats and mice is the formation of mono- and dihydroxy-3-methyloxindoles and their subsequent conjugation with glucuronic acid or sulfate. 8. There are no apparent qualitative differences in the biotransformation of 3MI between goats and mice that can account for their different sensitivities to 3MI-induced lung injury.

Animals↗