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PubMed1986

Piperine-mediated inhibition of glucuronidation activity in isolated epithelial cells of the guinea-pig small intestine: evidence that piperine lowers the endogeneous UDP-glucuronic acid content.

Piperine (1-peperoyl piperidine), a major component of the Piper species was reported recently by us to inhibit the activities of rat hepatic monooxygenases and UDP-glucuronyltransferase. This study explores further the basis of inhibition of glucuronidation. The effect of piperine on the rate of glucuronidation of 3-hydroxybenzo(a) pyrene and UDP-glucuronic acid content in the intact isolated epithelial cells of the guinea-pig small intestine was studied. The cells offered a fairly good system to study the modulation of glucuronidation activity. Glucuronidation of 3-hydroxybenzo(a) pyrene was dependent on the time of incubation, cellular protein and substrate concentration. From the kinetics of glucuronidation of 3-hydroxybenzo(a)pyrene in the isolated cell preparation the Vmax of 0.5 nmol of BP-3-glucuronide formed per min/mg of protein and Km of 25 microM were observed. The endogeneous concentration of UDP-glucuronic acid observed was 1.6 to 2.3 nmol/mg of cellular protein. Piperine caused a concentration-related decrease in UDP-glucuronic acid content and the rate of glucuronidation in the cells. It required much lower concentrations of piperine than D-galactosamine to diminish the endogeneous level of UDP-glucuronic acid. Rate of glucuronidation of 3-hydroxybenzo (a) pyrene was dependent on the endogeneous level of UDP-glucuronic acid. At 50 microM piperine, the rate of glucuronidation was reduced to about 50% of the basal rate. Piperine caused noncompetitive inhibition of hepatic microsomal UDP-glucuronyltransferase with Ki of 70 microM. The studies demonstrate that piperine modifies the rate of glucuronidation by lowering the endogeneous UDP-glucuronic acid content and also by inhibiting the transferase activity.

Alkaloids↗
PubMed2002

The donor substrate specificity of the human beta 1,3-glucuronosyltransferase I toward UDP-glucuronic acid is determined by two crucial histidine and arginine residues.

The human beta1,3-glucuronosyltransferase I (GlcAT-I) plays a key role in proteoglycan biosynthesis by catalyzing the transfer of glucuronic acid onto the trisaccharide-protein linkage structure Galbeta1,3Galbeta1,4Xylbeta-O-Ser, a prerequisite step for polymerization of glycosaminoglycan chains. In this study, we identified His(308) and Arg(277) residues as essential determinants for the donor substrate (UDP-glucuronic acid) selectivity of the human GlcAT-I. Analysis of the UDP-glucuronic acid-binding site by computational modeling in conjunction with site-directed mutagenesis indicated that both residues interact with glucuronic acid. Substitution of His(308) by arginine induced major changes in the donor substrate specificity of GlcAT-I. Interestingly, the H308R mutant was able to efficiently utilize nucleotide sugars UDP-glucose, UDP-mannose, and UDP-N-acetylglucosamine, which are not naturally accepted by the wild-type enzyme, as co-substrate in the transfer reaction. To gain insight into the role of Arg(277), site-directed mutagenesis in combination with chemical modification was carried out. Substitution of Arg(277) with alanine abrogated the activity of GlcAT-I. Furthermore, the arginine-directed reagent 2,3-butanedione irreversibly inhibited GlcAT-I, which was effectively protected against inactivation by UDP-glucuronic acid but not by UDP-glucose. It is noteworthy that the activity of the H308R mutant toward UDP-glucose was unaffected by the arginine-directed reagent. Our results are consistent with crucial interactions between the His(308) and Arg(277) residues and the glucuronic acid moiety that governs the specificity of GlcAT-I toward the nucleotide sugar donor substrate.

Arginine↗
PubMed1997

Fermentation of biomass-derived glucuronic acid by pet expressing recombinants of E. coli B.

The economics of large-scale production of fuel ethanol from biomass and wastes requires the efficient utilization of all the sugars derived from the hydrolysis of the heteropolymeric hemicellulose component of lignocellulosic feedstocks. Glucuronic and 4-O-methyl-glucuronic acids are major side chains in xylans of the grasses and hardwoods that have been targeted as potential feedstocks for the production of cellulosic ethanol. The amount of these acids is similar to that of arabinose, which is now being viewed as another potential substrate in the production of biomass-derived ethanol. This study compared the end-product distribution associated with the fermentation of D-glucose (Glc) and D-glucuronic acid (GlcUA) (as sole carbon and energy sources) by Escherichia coli B (ATCC 11303) and two different ethanologenic recombinants--a strain in which pet expression was via a multicopy plasmid (pLOI297) and a chromosomally integrated construct, strain KO11. pH-stat batch fermentations were conducted using a modified LB medium with 2% (w/v) Glc or GlcUA with the set-point for pH control at either 6.3 or 7.0. The nontransformed host culture produced only lactic acid from glucose, but fermentation of GlcUA yielded a mixture of ethanol, acetic, and lactic acids, with acetic acid being the predominant end-product. The ethanol yield associated with GlcUA fermentation by both recombinants was similar, but acetic acid was a significant by-product. Increasing the pH from 6.3 to 7.0 increased the rate of glucuronate fermentation, but it also decreased the ethanol mass yield from 0.22 to 0.19 g/g primarily because of an increase in acetic acid production. In all fermentations there was good closure of the carbon mass balance, the exception being the recombinant bearing plasmid pLOI297 that produced an unidentified product from GlcUA. The metabolism of GlcUA by this metabolically engineered construct remains unresolved. The results offered insights into metabolic fluxes and the regulation of pyruvate catabolism in the wild-type and engineered strains. End-product distribution for metabolism of glucuronic acid by the nontransformed, wild-type E. coli B and recombinant strain KO11 suggests that the enzyme pyruvate-formate lyase is not solely responsible for the production of acetylCoA from pyruvate and that derepressed pyruvate dehydrogenase may play a significant role in the metabolism of GlcUA.

Acetyltransferases↗
PubMed1984

Enzymatic determination of free glucuronic acid with glucuronolactone reductase. I. Isolation and purification of glucuronolactone reductase from rat kidney.

Glucuronolactone reductase [EC 1.1.1.20] from rat kidney was purified over 300-fold by ammonium sulfate fractionation, chromatography on DEAE-cellulose and hydroxylapatite columns, and preparative isoelectric focusing. The substrate specificity of the enzyme in the reduction reaction was broad, and hexuronic acid was one of the best substrates among monosaccharides. Km values for D-glucuronic acid, D-glucuronolactone, D-galacturonic acid, and L-iduronic acid were 6, 9, 4, and 6 mM, respectively. An investigation of the activity for aldose led to the finding that triose and tetrose served as good substrates for this enzyme. However, the activity for aldopentose or aldohexose was less than 1% of that for D-glucuronic acid at the same concentration. The enzyme was inactive towards most hexosamines (galactosamine, mannosamine, N-acetylglucosamine, N-acetylgalactosamine, and N-acetylmannosamine, but not glucosamine), meso-inositol, D-fructose, and tetrasaccharides from hyaluronic acid and chondroitin 4-sulfate. Trisaccharides from hyaluronic acid and chondroitin 6-sulfate which possess glucuronic acid at the reducing end were poor substrates for the enzyme and the activity towards these 4-substituted glucuronic acids was less than 3% of that towards non-substituted glucuronic acid.

Animals↗
PubMed1993

Determination of the human liver UDP-glucuronosyltransferase 2B4 domains involved in the binding of UDP-glucuronic acid using photoaffinity labeling of fusion proteins.

The interactions between UDP-glucuronic acid and two human liver UDP-glucuronosyltransferase 2B4 peptides (14-150 and 299-446) purified from E. coli as Staphylococcus aureus protein A fusion proteins have been investigated. Photoaffinity labeling with azidonucleotides ([beta-32P]5N3UDP-Glucuronic acid and [beta-32P]5N3UDP-Glucose) and competition experiments with UDP-glucuronic acid and structurally related compounds emphasized the presence of a specific UDP binding site between amino acids 299 and 446. Moreover, competition experiments strongly suggested an interaction between the amino terminal part of the protein and glucuronic acid. It would involve an electrostatic bond in the binding of the cosubstrate via the carboxyl group of UDP-glucuronic acid and a positively charged amino acid of the N-terminal domain of the enzyme.

Affinity Labels↗
PubMed1990

Role of nucleotide pyrophosphatase in enflurane-induced reduction of UDP-glucuronic acid concentration in mouse liver.

Because hepatic UDP-glucuronic acid levels decrease upon exposure to volatile anesthetics, the present study was designed to determine the mechanism by which enflurane decreases UDP-glucuronic acid in mice by measuring the concentrations of intermediates and the activities of enzymes in the UDP-glucuronic acid pathway. UDP-glucuronic acid concentrations were decreased by 40% in both male and female mice after 10 min of enflurane-induced narcosis. Concentration of UDP-glucose and the activities of diethylstilbestrol UDP-glucuronosyltransferase and UDP-glucose dehydrogenase were not affected by enflurane treatment. In contrast, nucleotide pyrophophatase activity was increased approximately 50% in both sexes. Thus, the decrease in hepatic UDP-glucuronic acid upon exposure of mice to enflurane is probably due to increased degradation by nucleotide pyrophosphatase.

Animals↗
PubMed1996

Uridine diphosphoxylose enhances hepatic microsomal UDP-glucuronosyltransferase activity by stimulating transport of UDP-glucuronic acid across the endoplasmic reticulum membrane.

The UDP-glucuronosyltransferase (UGT) system fulfils a pivotal role in the biotransformation of potentially toxic endogenous and exogenous compounds. Here we report that the activity of UGT in rat liver is stimulated by UDP-xylose. This stimulation was found in native microsomal vesicles as well as in the intact endoplasmic reticulum (ER) membrane, as studied in permeabilized hepatocytes, indicating the potential physiological importance of UDP-xylose in the regulation of UGT. We present evidence that UDP-xylose enhances UGT activity by stimulation of (i) the uptake of UDP-glucuronic acid across the ER membrane and (ii) the elimination of the UDP and/or UMP reaction product out of the ER lumen. UDP-xyloe produced a marked trans-stimulation of microsomal UDP-glucuronic acid uptake when it was present within the lumen of the ER. When UDP-xylose was presented at the cytosolic side of the ER, it acted as a weak inhibitor of UDP-glucuronic acid uptake. Likewise, cytosolic UDP-glucuronic acid strongly trans-stimulated efflux of intravesicular UDP-xylose, whereas cytosolic UDP-xylose was inefficient in trans-stimulating efflux of UDP-glucuronic acid. Microsomal UDP-xylose influx was markedly stimulated by UMP and UDP. Such stimulation was only apparent when microsomes had been preincubated and thereby preloaded with UMP or UDP, indicating that UMP and UDP exeted their effect on UDP-xylose uptake by trans-stimulation from the luminal side of the ER membrane.

Animals↗
PubMed1996

Trimetrexate glucuronate associated with anti-Kaposi sarcoma effect.

Trimetrexate glucuronate, a dihydrofolate reductase inhibitor related to methotrexate, was developed by Parke-Davis as an alternative antineoplastic agent for tumors, especially sarcomas, that had developed resistance to methotrexate. This is a report on a patient with AIDS who developed Pneumocystis carinii pneumonia, which was treated with trimethoprim sulfamethoxazole (Bactrim) with poor response, then with pentamidine with poor response, and finally with trimetrexate glucuronate (Neutrexin) and leucovorin rescue, with good response. The patient also suffered from cutaneous and visceral Kaposi's sarcoma (KS), which had been treated with high- dose HCG1 and well recognized chemotherapeutic protocols. Both HCG and chemotherapy resulted in tumor regression. The patient's KS flared, however, when he developed pneumocystis pneumonia. When trimetrexate glucuronate and leucovorin rescue were administered, his tumor burden decreased significantly, suggesting that trimetrexate glucuronate may have some activity against KS. The regression of KS in this anecdotal observation may be secondary to a delayed response from HCG and/or chemotherapy, or secondary to a spontaneous partial regression. Such regression may only be of the decreased edema around the KS lesions and not the neoplastic tissue itself. If other clinicians see this same phenomenon, however, it is possible that trimetrexate glucuronate may have an anti-KS effect. Such future clinical observations would warrant further testing at the basic science level.

AIDS-Related Opportunistic Infections↗
PubMed1979

[Radioenzymatic micromethod for the determination of UDP-glucuronic acid (author's transl)].

A new senitive and specific micromethod for determination of UDP-glucuronic acid is described Extracts from 2.5 mg of liver are incubated with twice washed guinea pig microsomes (as a source of UDP-glucuronyl transferase) and [14C]p-nitrophenol. The content of UDP-glucuronic acid is calculated from the [14C]p-nitrophenyl glucuronide/[14C]p-nitrophenol radioactivity ratio and the known amount of introduced [14C]p-nitrophenol. These values are corrected for losses of UDP-glucuronic acid by a calibration experiment, containing in addition to the aforementioned constituents, a known amount of UDP-glucuronic acid. The mean concentration of UDP-glucuronic acid in mice liver was found to be 171 mumol/kg wet weight.

Animals↗
PubMed1990

Biosynthesis of heparin. O-sulfation of D-glucuronic acid units.

Incubation of a microsomal fraction from murine mastocytoma, with UDP-[1-3H]GlcA, UDP-GlcNAc, and adenosine 3'-phosphate 5'-phosphosulfate (PAPS), yielded labeled, N-sulfated polysaccharides, in which most of the incorporated O-sulfate groups were located at C2 of L-iduronic acid and at C6 of D-glucosamine units. Analysis by anion-exchange high pressure liquid chromatography of disaccharides, generated by deaminative cleavage of these polysaccharides, revealed that, in addition, an appreciable portion of the -GlcNSO3-HexA-GlcNSO3- sequences in the intact polymers contained O-sulfated (at C2 or C3) D-glucuronic acid units. Calculations based on such compositional analysis of the N- and O-sulfated biosynthetic product, isolated by chromatography on DEAE-cellulose, showed that glucuronosyl 2/3-O-sulfate accounted for approximately 12% of the total incorporated O-sulfate groups. With [35S]PAPS (at a low total PAPS concentration) as an alternative source of label, the sulfated glucuronic acid residues were again detectable, albeit in much smaller amounts (1.8% of the total O-sulfate groups). Incorporation of label from UDP-[5-3H]GlcA was retained by the O-sulfated glucuronic acid units, thus demonstrating that these components had in fact been formed by sulfation of glucuronic acid residues and not by "back epimerization" of sulfated iduronic acid units. Structural analysis of polysaccharide intermediates at various stages of biosynthetic polymer modification, separated by ion-exchange chromatography, showed O-sulfation of glucuronic and iduronic acid units to appear simultaneously and before the 6-O-sulfation of glucosamine residues.

Animals↗
PubMed1977

Glucuronosyl diacylglycerol of Pseudomonas diminuta ATCC 11568. In vitro biosynthesis from UDP-glucuronate and diacylglycerol.

The biosynthesis of glucuronosyl diacylglycerol from UDP-glucuronate and diacylglycerol is catalyzed by an enzyme found in both the 34,800 X g supernatant and particulate preparations from disrupted Pseudomonas diminuta (ATCC 11586). UDP-glucuronate served as the glucuronosyl donor and could not be replaced by glucuronic acid, glucuronate-1-phosphate, and a number of nucleotide-linked sugars. The maximum velocity was estimated to be 19 nmol of glucuronosyl diacylglycerol synthesized/h/mg of protein in the presence of the 34,800 X g particulate enzyme and 63 nmol/h/mg of protein with the 34,800 X g supernatant preparation. The apparent Km for UDP-glucuronate was 4.2 micronM for supernatant and 4.4 to 6.0 micronM for particulate preparations. The biosynthesis of glucuronosyl diacylglycerol in vitro, was strongly dependent upon exogenous diacylglycerols containing unsaturated and shorter chain fatty acids. The enzymatic activity was very heat-labile and lost about 80% of the initial rate of synthesis after preincubation for 5 min at 37 degrees. The reaction was stimulated by 14.7 mM Triton X-100 and had an optimal pH of 7.1 and an ionic strength of 0.2 M. Divalent cations were not required.

Diglycerides↗
PubMed1965

REGULATION OF ASCORBIC ACID AND OF XYLULOSE SYNTHESIS IN RAT-LIVER EXTRACTS. THE EFFECT OF STARVATION ON THE ENZYMES OF THE GLUCURONIC ACID PATHWAY.

1. The synthesis of ascorbic acid in rat-liver extracts is impaired during starvation, and more from glucuronolactone and glucuronate than from gulonate and gulonolactone. 2. The formation of xylulose from gulonate and from gulonolactone is greatly enhanced during starvation, whereas it is decreased from glucuronolactone and from glucuronate. 3. The activity of the enzymes of the glucuronic acid pathway during starvation has been determined in rat-liver preparations. Gulonolactone oxidase is decreased, NAD-linked gulonate dehydrogenase is enhanced, and uronolactonase, aldonolactonase and NADP-linked hexonate dehydrogenase are unchanged. 4. The impairment of ascorbic acid synthesis from gulonate observed during starvation can be accounted for by the depressed activity of gulonolactone oxidase. 5. The cause of the enhanced formation of xylulose has been located in the sedimentable fraction of liver homogenate. 6. The hypothesis is formulated of an increased utilization of the glucuronic acid pathway during starvation.

Alcohol Oxidoreductases↗
PubMedDate not supplied

Mechanism of covalent adduct formation of diclofenac to rat hepatic microsomal proteins. Retention of the glucuronic acid moiety in the adduct.

The nonsteroidal antiinflammatory drug diclofenac can bind irreversibly to hepatocellular proteins via its acyl glucuronide metabolite. In view of a possible involvement of these protein adducts in the pathogenesis of diclofenac-associated liver damage, we investigated the mechanism of adduct formation in rat hepatic microsomes. [14C]Diclofenac covalently bound to hepatic microsomal proteins as a function of exposure time and the concentration of the cofactor, UDP-glucuronic acid (UDPGA). The rate and extent of protein binding were significantly increased in the presence of the imine-trapping agent, sodium cyanide. Moreover, hepatic microsomes incubated with [14C]UDPGA and nonradiolabeled diclofenac resulted in similar covalent binding of the radiolabeled compound to microsomal proteins. Covalent binding of [14C]UDPGA was significantly decreased in the presence of 7,7,7-triphenylheptyl-UDP, a specific inhibitor of UDP-glucuronosyltransferase. Finally, the protein adducts formed after incubation with both the radiolabeled aglycone and radiolabeled glucuronic acid were resolved by sodium dodecyl sulfate gel electrophoresis. Under both conditions, a radiolabeled protein band of apparent M(r) 60 kDa was found by fluorographic analysis. These results indicate that diclofenac acyl glucuronide covalently binds to hepatic microsomal proteins by two apparent mechanisms. Besides nucleophilic displacement of the glucuronic acid, the open-chain glucuronic acid can form an imine bond with a nucleophilic site of the target protein and is thus retained within the adduct.

Animals↗
PubMed1970

Measurement of uridine diphosphate glucuronic acid concentrations and synthesis in animal tissues.

1. A method for the isolation from animal tissues of UDP-glucuronic acid by one-dimensional paper chromatography is described and its concentrations in some tissues of several species of vertebrates are reported; the incorporation of [(32)P]-phosphate into UDP-glucuronic acid in vivo was also investigated. 2. The concentration of UDP-glucuronic acid was higher in the liver of rats, rabbits and guinea pigs than in the same tissue of some species of birds, amphibia and fishes; also, the concentration of UDP-glucuronic acid in rat liver, kidney and small intestine was several times lower than that of the same tissues of guinea pigs. 3. The rate of [(32)P]-phosphate incorporation into UDP-glucuronic acid was very high in rat liver and kidney and almost reached equilibrium with the radioactivity of UDP-glucose 30min after the administration of the [(32)P]phosphate.

Animals↗
PubMed1983

Glucuronic acid-containing glycopeptide from squid cartilage.

A glycopeptide fraction containing glucuronic acid as a component sugar was extracted and purified from squid cartilage to give a single band migrating much slower than hyaluronic acid in cellulose acetate electrophoresis. The molecular weight of the glycopeptide was fairly large since its Kav value in Sephadex G-200 chromatography was 0.18; however, it was soluble in 66% ethanol. This glycopeptide contained glucuronic acid, glucosamine, galactosamine, galactose, and fucose. The total amino acid content was 1.87 mumol of amino acid per mg of the glycopeptide. Threonine, serine and proline represented 80% of the amino acids. Digestion with chondroitinase ABC or reaction with nitrous acid did not result in degradation of the glycopeptide; however, it was completely degraded by reaction with 0.5 M KOH at 37 degrees C. Two hexasaccharides were separated from the alkaline degradation products, and they both contained glucuronic acid, fucose, galactosamine, and reducing terminal glucosamine in the molar ratio, 2:1:2:1. These results indicated that the glycopeptide contains glucuronic acid-containing sugar chains that are distinct from any known glycosaminoglycan.

Amino Acids↗
PubMed1988

Effect of dietary terpenes on glucuronic acid excretion and ascorbic acid turnover in the brushtail possum (Trichosurus vulpecula).

1. Glucuronic acid was excreted in the urine of the brushtail possum, Trichosurus vulpecula, in response to dietary terpenes (essential oils found in Eucalyptus foliage). 2. The relationship between urinary glucuronic acid and the estimated terpene content of the diet was not equimolar, but varied from 1-17%, with levels of 5-39% found in animals maintained on terpenes or eucalypt leaves for several weeks. 3. Blood levels of ascorbate and the turnover rate of ascorbate were increased in the brushtail possum in response to dietary terpenes. 4. The presence of an active glucuronic acid pathway and associated glucose-ascorbate-glucose cycle was postulated for the brushtail possum and the other arboreal marsupials, Pseudocheirus peregrinus (common ringtail possum) and Petauroides volans (greater glider). 5. By means of these pathways these animals may utilise the high ascorbate content of Eucalyptus leaves to conserve glucose required for synthesis of glucuronic acid used for conjugation of dietary terpenes.

Animals↗
PubMed1995

Identification of O-sulphate substituents on D-glucuronic acid units in heparin-related glycosaminoglycans using novel synthetic disaccharide standards.

The two disaccharides, methyl 4-O-(2-O-sulpho-beta-D-glucopyranosyl-uronic acid)-2-deoxy-2-amino-alpha-D-glucopyranoside and methyl 4-O-(3-O-sulpho-beta-D-glucopyranosyluronic acid)-2-deoxy-2-amino-alpha-D-glucopyranoside, were prepared by de novo synthesis, and converted to the corresponding 2,5-anhydro-D-[1-3H]mannitol derivatives by deamination with nitrous acid followed by reduction with NaB3H4. The resultant labelled products were used as standards in the identification, by anion-exchange high-performance liquid chromatography (HPLC), of disaccharides generated by HNO2/NaB3H4 treatment of heparan sulphate isolated from human brain. The two standards, containing 2-O- and 3-O-sulphated glucuronic acid, respectively, were clearly separated by the HPLC procedure. Comparison with the deamination products derived from heparan sulphate showed that the mono-O-sulphated disaccharide species containing a sulphated glucuronic acid unit co-eluted with the 2-O-sulphated standard. The corresponding component isolated from other heparan sulphate preparations, or from heparin, also eluted at the same position. No disaccharide derived from heparin or heparan sulphate appeared at the elution position of the 3-O-sulphated standard. It is concluded that D-glucuronic acid units in heparin-related glycosaminoglycans may be sulphated at C2, whereas no evidence has been found for sulphation at C3. By contrast, analysis of mono-O-sulphated disaccharides derived from a chemically sulphated, bacterial capsular polysaccharide (generated by Escherichia coli K5) clearly demonstrated the occurrence of O-sulphate groups at C-3 of D-glucuronic acid units.

Carbohydrate Sequence↗
PubMed1982

The excretion of metabolites of the D-glucuronic acid pathway in human urine. Effect of phenobarbitone administration.

1. The urinary excretion of four metabolites of the D-glucuronic acid pathway, namely D-glucaric acid, free (unconjugated) D-glucuronic acid, L-gulonic acid and xylitol, has been studied in normal male volunteers and in male and female epileptic patients receiving phenobarbitone anticonvulsant therapy. 2. In normal male subjects the urinary excretion of the D-glucuronic acid metabolites, expressed per unit of creatinine, was similar in first void and total (24 h) urine samples and was fairly constant over a period of 4 weeks. 3. In male and female epileptic patients phenobarbitone treatment enhanced the urinary excretion of D-glucaric acid and xylitol and the combined excretion of D-glucaric acid, l-gulonic acid and xylitol. 4. It is suggested that the measurement of a spectrum of urinary D-glucuronic acid metabolites may provide a more reliable index for assessment of the induction of hepatic xenobiotic-metabolizing enzyme activities in man than the determination of urinary D-glucaric acid alone.

Adult↗