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PubMed1992

1H-N.m.r. spectral assignments for two series of heparin-derived oligosaccharides.

Six heparin-derived oligosaccharides, ranging in size from di- to octa-saccharide and forming two closely related series differing in structure by the substitution of an unsulfated D-glucuronate for a 2-sulfated L-iduronate residue, have been characterized by 2-dimensional 1H-n.m.r. spectroscopy. In addition to providing new data on hexa- and octa-saccharides, several important changes to previously published data have been found for the two tetrasaccharides. The D-glucuronic acid H-5 proton is assigned to a resonance in the same region as resonances for the H-3 and H-4 D-glucuronate protons, rather than downfield from these resonances as earlier reported. The presence of D-glucuronic acid in the heparin sequence of the series-1 fragments affects the positions of neighboring D-glucosamine resonances, in particular shifting the anomeric proton signal in the preceding D-glucosamine 0.1-0.2 p.p.m. downfield. Resonances from the reducing-end D-glucosamines differ from internal D-glucosamine resonances both in relative position and in the degree of chemical shift difference between the H-6 and H-6' protons. This work illustrates the usefulness of two-dimensional techniques in determining heparin structure and emphasizes the need for direct analysis, rather than assignment by comparison to model compounds.

Carbohydrate Sequence↗
PubMed2005

Amaranthin in feather cockscombs is synthesized via glucuronylation at the cyclo-DOPA glucoside step in the betacyanin biosynthetic pathway.

Uridine 5'-diphosphate (UDP)-glucuronic acid: cyclo-DOPA 5-glucoside glucuronosyltransferase activity was detected in a crude extract prepared from the purple flowers of feather cockscombs. This suggests that the glucuronic acid moiety of amaranthin and its derivatives may be introduced at the cyclo-DOPA glucoside step, but not at the betanidin glucoside step.

Betacyanins↗
PubMed1988

Hepatic detoxification and hepatic function in chronic active hepatitis with and without cirrhosis.

The detoxification capacity of the liver in chronic active hepatitis (CAH) without liver cirrhosis (LC) is not sufficiently known. Therefore, we examined, in 156 patients with morphologically proven CAH of different stages, plasma ammonia, free phenols, indican, glucuronic acid and urea synthesis rate as parameters for liver detoxification. We found a significant increase of ammonia, phenols, and indican and a significant decrease of glucuronic acid and urea synthesis rate parallel to the stage of CAH without LC. In 34 CAH patients with complete recovery, a retrospective 10-year follow-up was possible. Parallel to the normalization of liver morphology and general liver tests, detoxification parameters also normalized. However, the detoxification disorders in CAH without LC are mild in nature and do not produce hepatic encephalopathy. Probably, they are caused by a reduced synthesis of the urea-cycle enzymes and of glucuronyltransferase in the liver.

Ammonia↗
PubMed1991

Nucleotide profile in rat liver and intestine at portal vein obstruction and reflow.

Liver and intestinal nucleotides and energy charge levels were examined in rats at portal vein clamping for 1, 5 or 30 min and after reflow for 1 or 6 h following 30 min clamping. In both tissues, clamping resulted in a loss of ATP, energy charge, UTP, GTP, UDP-glucuronic acid and UDP-N-acetylhexosamine levels, which all, except ATP and total adenosine phosphates, essentially recovered at 1 h reflow. At 6 h reflow, liver UDP-glucuronic acid and liver glutathione decreased in both clamped and sham operated rats.

Animals↗
PubMed1991

The effects of temporary occlusion of the superior mesenteric vein or splenic vein on biliary bilirubin and bile acid excretion in rats.

To elucidate the possible implication of hepatic blood supply to the occurrence of hepatolithiasis, the rat superior mesenteric vein, which drains blood from the intestine, or the splenic vein, which drains from the spleen, was occluded for 30 minutes. Changes in the hepatic oxygen saturation index, intrahepatic uridine diphosphate-glucuronic acid concentration, bile flow, and the excretion of bilirubin as well as its fraction, along with bile acid in bile before and after the procedure, were observed. In association with superior mesenteric vein occlusion, oxygen saturation index, hepatic uridine diphosphate-glucuronic acid concentration, bile flow, bile acid concentration in bile, and percentage of biliary bilirubin diglucuronide were all decreased. Incubation of bile under sterile conditions from rats with occluded superior mesenteric veins resulted in precipitation of mainly calcium salt of fatty acid. In contrast, splenic vein occlusion caused no changes except for a decrease in biliary bilirubin concentration. Incubation of bile from rats with occluded splenic veins did not induce precipitation. From these findings it can be concluded that blood flow in the superior mesenteric vein is the primary source of oxygen supply to the rat liver and that this vein plays an important role in maintaining bile flow, bile acid excretion, and bilirubin conjugation and in preventing the precipitation of bile (possibly preventing hepatolithiasis).

Animals↗
PubMed2004

Quaternary ammonium-linked glucuronidation of tamoxifen by human liver microsomes and UDP-glucuronosyltransferase 1A4.

Tamoxifen (TAM), a nonsteroidal antiestrogen, is the most widely used drug for chemotherapy of hormone-dependent breast cancer in women. In the present study, we found a new potential metabolic pathway of TAM via N-linked glucuronic acid conjugation for excretion in humans. TAM N(+)-glucuronide was isolated from a reaction mixture consisting of TAM and human liver microsomes fortified with UDP-glucuronic acid (UDPGA) and identified with a synthetic specimen by high-performance liquid chromatography-electrospray ionization-mass spectrometry. However, no TAM-glucuronidating activity was detected in microsomes from rat, mouse, monkey, dog, and guinea pig livers. A strong correlation (r(2) =0.92 ) was observed between N-glucuronidating activities toward TAM and trifluoperazine, a probe substrate for human UDP-glucuronosyltransferase (UGT) 1A4, in human liver microsomes from eight donors (five females, three males). However, no correlation ( (r(2) =0.02 )) was observed in the activities between 7-hydroxy-4-(trifluoromethyl)coumarin and TAM. Only UGT1A4 catalyzed the N-linked glucuronidation of TAM among recombinant UGTs (UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A9, UGT2B4, UGT2B7, UGT2B15, and UGT2B17) expressed in insect cells. Apparent K(m) values for TAM N-glucuronidation by human liver microsomes and recombinant UGT1A4 were 35.8 and 32.4 microM, respectively. These results strongly suggested that UGT1A4 could play a role in metabolism and excretion of TAM without Phase I metabolism in human liver. TAM N(+)-glucuronide still had binding affinity similar to TAM itself for human estrogen receptors, ERalpha and ERbeta, suggesting that TAM N(+)-glucuronide might contribute to the biological activity of TAM in vivo.

Adult↗
PubMed1976

The properties of uridine diphosphate glucuronyltransferase(s) which catalyse the synthesis of steroid glucuronides in microsomal fractions from guinea-pig liver.

The properties of the UDP-glucuronyltransferase(s) of guinea-pig liver that catalyse the synthesis of steroid glucuronides were examined. There are many similarities between apparently different substrate-specific forms of these enzymes in that all are activated by bivalent metal ions, and all contain at least 2 thiol groups important for enzyme activity. On the other hand, there are significant differences between the enzymes conjugating steroids and those conjugating non-steroids. Only the latter are activated by UDP-N-acetylglucosamine, which enhances their relatively poor affinity for UDP-glucuronic acid. The steroid-conjugating forms of UDP-glucuronyltransferase are not activated by UDP-N-acetylglucosamine and have relatively high apparent affinities for UDP-glucuronic acid. The rate of glucuronidation of testosterone was inhibited by treatment with phospholipase A. Treatment with cholate or Triton X-100 did not enhance the rates of glucuronidation of any steroid tested. The data indicate several similarities between different forms of UDP-glucuronyltransferase, suggesting that there is a large family of related proteins. At the same time there are important differences in the parameters that modulate the rates of different glucuronidation reactions.

Animals↗
PubMed2000

13C NMR relaxation studies on cartilage and cartilage components.

We have investigated the molecular motions of polysaccharides of bovine nasal and pig articular cartilage by measuring the 13C NMR relaxation times (T1 and T2). Both types of cartilage differ significantly towards their collagen/glycosaminoglycan ratio, leading to different NMR spectra. As chondroitin sulfate is the main constituent of cartilage, aqueous solutions of related poly- and monosaccharides (N-acetylglucosamine and glucuronic acid) were also investigated. Although there are only slight differences in T1 relaxation of the mono- and the polysaccharides, T2 decreases about one order of magnitude, when glucuronic acid or N-acetylglucosamine and chondroitin sulfate are compared. It is concluded that the ring carbons are motion-restricted primarily by the embedment in the rigid pyranose structure and, thus, additional limitations of mobility do not more show a major effect. Significant differences were observed between bovine nasal and pig articular cartilage, resulting in a considerable line-broadening and a lower signal to noise ratio in the spectra of pig articular cartilage. This is most likely caused by the higher collagen content of articular cartilage in comparison to the polysaccharide-rich bovine nasal cartilage.

Acetylglucosamine↗
PubMed1969

Structural studies on colanic acid, the common exopolysaccharide found in the enterobacteriaceae, by partial acid hydrolysis. Oligosaccharides from colanic acid.

The exopolysaccharide slime colanic acid has been isolated from representative strains of Escherichia coli, Salmonella typhimurium and Aerobacter cloacae. Analysis showed that each polymer contained glucose, galactose, fucose and glucuronic acid, together with acetate and pyruvate. The molar proportions of these components were 1:1.8:1.9:1:1:1 approximately. On the basis of periodate oxidation of the natural and deacetylated polysaccharide, glucose is proposed as the site of the acetyl groups. The pyruvate is attached to galactose. Three neutral oligosaccharides and ten electrophoretically mobile oligosaccharides were isolated and partially characterized. Four of the fragments were esters of pyruvic acid. Most oligosaccharides were isolated from all three polysaccharide preparations. Three further oligosaccharides were isolated from carboxyl-reduced colanic acid and sodium borotritide was used to label the glucose derived from glucuronic acid in these fragments. One trisaccharide was obtained from periodate-oxidized polysaccharide. On the basis of these oligosaccharides a repeating hexasaccharide unit of the following structure is proposed: [Formula: see text] The significance of this structure in colanic acid biosynthesis is discussed.

Acetates↗
PubMedDate not supplied

Modulative effects of metabolic effectors on benzo(a)pyrene-induced cytotoxicity and mutagenicity in mammalian cells.

Conjugation and detoxification of mixed function oxidase (MFO)-mediated benzo(a)pyrene [B(a)P] metabolites with glucuronic acid and glutathione (GSH) are major pathways of B(a)P elimination and ultimately excretion in vivo. We have studied the effects of uridine diphosphate alpha-D-glucuronic acid (UDPGA) and GSH, a cofactor for the synthesis of glucuronide and GSH conjugates, respectively, on B(a)P-induced cytotoxicity and mutagenicity in mammalian cells. The S9-mix used in the Chinese hamster ovary cell/hypoxanthine-guanine phosphoribosyltransferase (CHO/HPRT) mutational assay was supplemented with either UDPGA, GSH, or GSH plus purified GSH-S-transferases (GSHTs), to study modulation of glucuronide and GSH detoxification mechanisms on B(a)P-induced cytotoxic and mutagenic effects. We found that the addition of UDPGA to S9-mix reduces cytotoxicity induced by either B(a)P or B(a)P 6-OH but not by B(a)P 7,8-diol [B(a)P-diol]. The reduction of B(a)P and B(a)P 6-OH-induced cytotoxicity by glucuronide conjugation is likely due to elimination of cytotoxic phenols and quinones. The addition of GSH to the S9-mix resulted in a reduction of B(a)P- and B(a)P-diol-induced cytotoxicity. GSH plus GSHT reduced B(a)P-induced cytotoxicity and mutagenicity. GSH inhibited the mutagenicity at low concentrations of B(a)P-diol. GSH plus GSHTs inhibited the cytotoxicity and mutagenicity of B(a)P-diol at concentrations not affected by GSH alone. These studies demonstrate that mechanisms of detoxification can affect the biological activity of B(a)P and B(a)P-diol as profoundly as bioactivation by the MFO system. Future research should address studies of mutagenicity modulation by metabolic effectors at both the molecular (DNA sequence) and cellular (quantitative mutagenesis) level.

Animals↗
PubMed1992

Electron impact and fast atom bombardment mass spectrometric analysis of the food-borne carcinogens 2-amino-3-methylimidazo [4,5-f] quinoline, 2-amino-3,8-dimethylimidazo [4,5-f] quinoxaline and their metabolites.

Electron impact (EI) and fast atom bombardment (FAB) mass spectrometry were used to characterize the heterocyclic aromatic amines, 2-amino-3-methylimidazo[4,5-f]quinoline and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline and their metabolites. The carcinogenic N2-hydroxy metabolites and several non-conjugated detoxification products were analysed directly by EI mass spectrometry, while several polar sulphate and beta-glucuronic acid conjugates were analysed by FAB mass spectrometry. Analysis of beta-glucuronic acid conjugates was also achieved by EI mass spectrometry following silylation.

Carcinogens↗
PubMed1986

Formation of dermatan sulfate by cultured human skin fibroblasts. Effects of sulfate concentration on proportions of dermatan/chondroitin.

[3H,35S]Dermatan/chondroitin sulfate glycosaminoglycans produced during culture of fibroblasts in medium containing varying concentrations of sulfate were tested for their susceptibility to chondroitin ABC lyase and chondroitin AC lyase. Chondroitin ABC lyase completely degraded [3H]hexosamine-labeled and [35S] sulfate-labeled dermatan/chondroitin sulfate to disaccharides. Chondroitin AC lyase treatment of the labeled glycosaminoglycans produced different results. With this enzyme, dermatan/chondroitin sulfate formed at high concentrations of sulfate yielded small glycosaminoglycans and larger oligosaccharides but almost no disaccharide. This indicated that the dermatan/chondroitin sulfate co-polymer contained mostly iduronic acid with only an occasional glucuronic acid. As the medium sulfate concentration was progressively lowered, there was a concomitant increase in the susceptibility to degradation by chondroitin AC lyase. Thus, the labeled glycosaminoglycans formed at the lowest concentration of sulfate yielded small oligosaccharides including substantial amounts of disaccharide. The smaller chondroitin AC lyase-resistant [3H,35S]dermatan/chondroitin sulfate oligosaccharides were analyzed by gel filtration. Results indicated that, in general, the iduronic acid-containing disaccharide residues present in the undersulfated [3H,35S]glycosaminoglycan were sulfated, whereas the glucuronic acid-containing disaccharide residues were non-sulfated. This work confirms earlier reports that there is a relationship between epimerization and sulfation. Moreover, it demonstrates that medium sulfate concentration is critical in determining the proportions of dermatan to chondroitin (iduronic/glucuronic acid) produced by cultured cells.

Adult↗
PubMed1994

Determination of structural elements of the L2/HNK-1 carbohydrate epitope required for its function.

The L2/HNK-1 carbohydrate epitope has been shown to carry an unusual 3'-sulfoglucuronic acid linked O-glycosidically through a neolactosyl-type backbone to a ceramide residue. Using monoclonal antibodies, the same or a closely related epitope has also been detected N-glycosidically linked to glycoproteins, amongst them several neural cell adhesion molecules. We used synthetic glycolipids carrying sulfated or non-sulfated glucuronic acid attached to ceramide through glycans of different length to show that not only the sulfated glucuronic acid but also the neolactosyl-type backbone is essential for the recognition of the L2/HNK-1 carbohydrate by a monoclonal antibody, its binding to laminin and its role in neural cell migration and outgrowth of processes from neurons and astrocytes.

Animals↗
PubMed1993

Sequential assembly and polymerization of the polyprenol-linked pentasaccharide repeating unit of the xanthan polysaccharide in Xanthomonas campestris.

Lipid-linked intermediates are involved in the synthesis of the exopolysaccharide xanthan produced by the bacterium Xanthomonas campestris (L. Ielpi, R. O. Couso, and M. A. Dankert, FEBS Lett. 130:253-256, 1981). In this study, the stepwise assembly of the repeating pentasaccharide unit of xanthan is described. EDTA-treated X. campestris cells were used as both enzyme preparation and lipid-P acceptor, and UDP-Glc, GDP-Man, and UDP-glucuronic acid were used as sugar donors. A linear pentasaccharide unit is assembled on a polyprenol-P lipid carrier by the sequential addition of glucose-1-P, glucose, mannose, glucuronic acid, and mannose. The in vitro synthesis of pentasaccharide-P-P-polyprenol was also accompanied by the incorporation of radioactivity into a polymeric product, which was characterized as xanthan, on the basis of gel filtration and permethylation studies. Results from two-stage reactions showed that essentially pentasaccharide-P-P-polyprenol is polymerized. In addition, the direction of chain elongation has been studied by in vivo experiments. The polymerization of lipid-linked repeat units occurs by the successive transfer of the growing chain to a new pentasaccharide-P-P-polyprenol. The reaction involves C-1 of glucose at the reducing end of the polyprenol-linked growing chain and C-4 of glucose at the nonreducing position of the newly formed polyprenol-linked pentasaccharide, generating a branched polymer with a trisaccharide side chain.

Carbohydrate Sequence↗
PubMed1994

Ascorbic acid-2-0-beta-glucuronide, a new metabolite of vitamin C identified in human urine and uremic plasma.

A new metabolite of ascorbic acid has been isolated by a multi-step chromatographic procedure both from normal human urine and uremic plasma. Nuclear Magnetic Resonance studies, and chemical and enzymic analyses indicated that the compound is a conjugated structure consisting of equimolar ascorbic and beta-D-glucuronic acids. We determined the pKa value of the ascorbic acid moiety of the compound on the basis of variations of ultraviolet absorbances as a function of pH. Results showed that glucuronic acid is coupled to the 2-position of ascorbic acid.

Ascorbic Acid↗
PubMed1987

Diphenylthiazole-induced changes in renal ultrastructure and enzymology: toxicologic mechanisms in polycystic kidney disease?

The mechanism by which various chemicals induce renal cystic disease is unknown. To examine the early events in cystogenesis the ultrastructure and biochemistry of liver and kidney were analyzed after the administration of a chemical that induces renal cyst formation. Special emphasis was placed on examining potential mechanisms that would account for the observed loss of extracellular proteoglycans. Renal cystic disease was chemically induced in rats by feeding 2-amino-4,5-diphenylthiazole (DPT) for up to 4 weeks. After 4 days of feeding, DPT had induced a 4-fold increase in total urine output relative to diet-restricted control groups. Both groups maintained, but did not gain, weight during the feeding schedule. Cyst formation was localized to the medullary collecting tubules. Relative to diet-restricted controls, rats fed DPT exhibited diminished renal and hepatic catalase activity, but elevated activity for UDP-glucuronosyltransferase. Medulla showed an increase in the specific activities of the enzymes galactosyltransferase and sulfatase B. These enzymological findings correlated with ultrastructural observations of a loss of peroxisomes, proliferation of endoplasmic reticulum and enlargement of the golgi apparatus. Serum and urinary levels of inorganic sulfate were significantly increased in DPT-fed rats relative to controls. Tissue levels of UDP-glucuronic acid and adenosine 3'-phosphate 5'-phosphosulfate were not depressed by DPT feeding. Thus, DPT-induced cyst formation and loss of staining for glycosaminoglycans does not involve gross depletions of UDP-glucuronic acid and adenosine 3'-phosphate 5'-phosphosulfate, mutual cosubstrates for Phase II drug conjugation reactions and glycosaminoglycan synthesis.

Animals↗
PubMedDate not supplied

Covalent binding of zomepirac glucuronide to proteins: evidence for a Schiff base mechanism.

Carboxylic acids can undergo irreversible binding to proteins via their acyl glucuronide metabolites. Such binding occurs in humans and in vitro for bilirubin and the anti-inflammatory drugs zomepirac and tolmetin and may have toxicological significance. The mechanism of the binding is uncertain, but is thought to involve nucleophilic displacement of glucuronic acid by free cysteine thiols, tyrosine, or lysine residues of the protein. We now present evidence, using zomepirac glucuronide, for an alternative mechanism where irreversible binding occurs by isomerization of the glucuronide and formation of an imine linkage between the glucuronic acid moiety of the conjugate and a lysine or terminal amino group of the protein. Involvement of a protein thiol in the binding mechanism was ruled out by experiments with the thiol blocking agent, p-hydroxymercuribenzoate. Moreover, significant irreversible binding occurred when the cysteine free protein, alpha s1-casein, was incubated in solution with zomepirac glucuronide in vitro. When zomepirac glucuronide was added to solutions with albumin in the presence of the imine trapping reagent, sodium cyanide, or the reducing agent, sodium cyanoborohydride, irreversible binding of zomepirac increased 8.3- and 5.5-fold relative to controls, respectively, after 6 hr at 37 degrees C. The product formed after treatment of solutions of zomepirac glucuronide and albumin with sodium cyanoborohydride was stable in dilute acid, whereas similar acid treatment of zomepirac-albumin adduct from control incubations, obtained after sodium cyanide exposure, released 30% of the total adduct. Only isomeric conjugates of zomepirac glucuronide were released from zomepirac-albumin adduct by mild acid; no beta 1-isomer was detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2002

The Caenorhabditis elegans vulval morphogenesis gene sqv-4 encodes a UDP-glucose dehydrogenase that is temporally and spatially regulated.

The development of the Caenorhabditis elegans vulva requires the involution of epithelial cells and provides a model for organ morphogenesis. Mutations in C. elegans sqv (squashed vulva) genes affect both vulval morphogenesis and embryonic development. We found that sqv-4 encodes a protein similar to UDP-glucose dehydrogenases and showed that the SQV-4 protein specifically catalyzes the conversion of UDP-glucose to UDP-glucuronic acid, which is essential for the biosynthesis of chondroitin and heparan sulfate proteoglycans. SQV-4 is expressed in the vulva and in oocytes, among many other cells, and SQV-4 levels are dramatically increased in a specific subset of vulval cells during vulval morphogenesis. We propose that the regulation of UDP-glucuronic acid production in a specific subset of vulval cells helps determine the shape of the vulva.

Amino Acid Sequence↗