Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.2.1.31 (beta-glucuronidase)
7,680 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Evidence was found for UDPglucuronyltransferase-catalysed deconjugation of p-nitrophenol-, 4-methylumbelliferone- and phenolphthalein-glucuronides. The evidence is based on the following observations: 1, deconjugation is UDP-dependent and the reactions show Michaels-Menten kinetics with respect to UDP and glucuronide saturability; 2, UDP-glucuronic acid was identified as reaction product; 3, all studies were done in the presence of a beta-glucuronidase inhibitor; 4, induction profiles, using 3-methylcholanthrene and phenobarbital as inducing agents, were identical for conjugation and deconjugation reactions. Optimal deconjugation rates for p-nitrophenol- and 4-methylumbelliferone-glucuronides were at pH 5.1 and for phenolphthalein-glucuronide at pH 6.5. Only conjugation reactions showed latency; the corresponding deconjugation reactions were not latent. UDPglucuronyltransferase is a group of oligomeric isoenzymes with different molecular masses. The molecular masses of the isoenzyme species catalysing the forward and reverse reactions were determined by radiation-inactivation analysis. The molecular masses of the isoenzyme species mediating the catalyses of deconjugation reactions were significantly smaller than those mediating catalyses of conjugation reactions: 66 +/- 4 kDa vs. 109 +/- 7 kDa for p-nitrophenol; 82 +/- 8 kDa vs. 105 +/- 6 kDa for 4-methylumbelliferone; and 74 +/- 8 kDa vs. 159 +/- 14 kDa for phenolphthalein. This suggests that for catalyses of deconjugation reactions only part of a UDPglucuronyltransferase isoenzyme is needed, whereas for forward reactions the complete isoenzymes are required.
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PMID:Deconjugation of glucuronides catalysed by UDPglucuronyltransferase. 309 62

1. The thio-beta-d-glucosiduronic acids (thio-beta-glucuronides) of o-aminothiophenol, diethyldithiocarbamic acid, p-nitrothiophenol and thiophenol are formed biosynthetically in broken- and intact-cell preparations of mouse liver. 2. For this biosynthesis to occur in homogenates or microsomal fractions, UDP-glucuronic acid was required during incubation; glucose, glucuronic acid or UDP could not replace it. UDP was a product of the reaction. 3. The biosynthetic mechanism linking glucuronic acid to thiol and carbodithioic groups therefore requires UDP-glucuronyltransferase activity and resembles that forming the various types of O-glucuronides. 4. An analogous enzymic mechanism employing UDP-glucose synthesizes the thio-beta-d-glucosides of diethyldithiocarbamic acid and thiophenol in gut preparations of the mollusc Arion ater; this mechanism resembles that forming the O-glucosides. The thio-beta-d-glucosides are formed also in intact cells. 5. As expected from the distribution of O-glycosides, S-glucuronides of these aglycones were not detectable with the invertebrate, nor were the S-glucosides with the vertebrate. 6. Despite their similar biosyntheses, S- and O-beta-glycosides differ in susceptibility to hydrolysis by beta-glycosidases. Rat preputial-gland beta-glucuronidase hydrolysed thioglucuronides of o-aminothiophenol, diethyldithiocarbamic acid and p-nitrothiophenol, hydrolysis being inhibited by glucarolactone; the thioglucuronide of thiophenol was not hydrolysed by preputial-gland or liver beta-glucuronidase. The two S-glucosides resisted hydrolysis by beta-glucosidase from almond emulsin.
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PMID:Mechanism of biosynthesis of thio- -D-glucuronides and thio- -D-glucosides. 465 87

1. After intravenous injections of radioactive thyroxine into cats, about half the radioactivity excreted in the bile was in a glucuronide fraction, which, after hydrolysis with beta-glucuronidase, gave rise to radioactive thyroxine and a radioactive substance that ran with 3,3',5'-tri-iodothyronine on paper chromatography in two dimensions. 2. The proportion of the total radioactivity in the bile in the glucuronide fraction was unaffected by an intravenous injection of 750mug. of non-radioactive thyroxine. 3. It is concluded that the capacity of the liver for forming the glucuronides of thyroxine and its metabolites is at least as great in cats as in monkeys. 4. These findings are discussed in relation to the question whether the liver contains one or more than one UDP-glucuronic acid glucuronyltransferase.
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PMID:Excretion of the glucuronide of thyroxine in cat bile. 495 52

1. Bilirubin glucuronide was synthesized in vitro in a system containing a rat liver microsomal fraction, UDP-glucuronic acid, Mg(2+) and bilirubin. The enzymic synthesis was accomplished without the addition of a bilirubin carrier. 2. Azobilirubin and azobilirubin glucuronide were separated by t.l.c. and paper chromatography and the measurement of the conjugate provided a specific assay for bilirubin UDP-glucuronyltransferase (EC 2.4.1.17). 3. This diazo compound was labelled when [U-(14)C]UDP-glucuronic acid was employed in the transglucuronidation reaction. 4. Identity of the glucuronide nature of the product was further confirmed by hydrolysis with beta-glucuronidase prepared from limpets and Helix pomatia. In each instance azobilirubin and glucuronic acid were liberated. 5. There was a close correlation between the bilirubin glucuronyl-transferase activity as measured by two procedures, colorimetric and radioisotopic. The specific activities so measured were 19nmol of bilirubin ;equivalents' conjugated/h per mg of protein and 16.9-18.4nmol of UDP-glucuronic acid incorporated/h per mg of protein, respectively. On this basis, it was concluded that the major product formed in vitro was bilirubin monoglucuronide; this represents about 77% of the total products formed. 6. The K(m) values for bilirubin and UDP-glucuronic acid at pH8.2 are 3.3x10(-4)m and 1.67x10(-3)m, respectively. 7. The addition of Mg(2+) at a final concentration of 5mm to the reaction mixture increased the rate of conjugation by 5.6-fold in the microsomal preparation that had been subjected to overnight dialysis against 10mm-EDTA (disodium salt). 8. Diethyl-nitrosamine at a final concentration of 1-20mm has no effect on the glucuronidation of bilirubin in vitro.
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PMID:Bilirubin glucuronyltransferase. Specific assay and kinetic studies. 515 13

The dietary addition of several xenobiotics, such as PCB, DDT, aminopyrine, chloretone, BHT and BHA, caused significant increases in the ascorbic acid in urine and liver of rats. The administration of all types of xenobiotics used in the present experiments increased the activity of hepatic UDP-glucose dehydrogenase (1.3-2.8-fold), and the administration of PCB, DDT, BHT or BHA significantly increased the activity of hepatic UDP-glucuronyl transferase (2.2-13.1-fold). The activity of beta-glucuronidase was slightly increased with feeding of PCB, DDT, chloretone or aminopyrine. However, the activity of hepatic UDP-glucuronic acid pyrophosphatase, the conversion of D-glucuronic acid or D-glucuronolactone into L-ascorbic acid and the activity of hepatic L-gulonolactone oxidase did not increase with the administration of PCB or DDT. It is suggested that the increases in the activities of UDP-glucose dehydrogenase and UDP-glucuronyl transferase would have a major role in the stimulation of ascorbic acid synthesis in xenobiotic treated rats.
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PMID:Effect of several xenobiotics on the activities of enzymes affecting ascorbic acid synthesis in rats. 613 23

Rates of production of p-nitrophenyl glucuronide by isolated perfused livers from fed or fasted phenobarbital-treated rats were estimated by monitoring the concentration of glucuronide in the effluent perfusate. Infusion of epinephrine decreased the steady state level of p-nitrophenyl glucuronide by about 39% (half-maximal inhibition at approximately 5 microM). This result was unexpected because epinephrine activated glycogenolysis and elevated hepatic UDP-glucuronic acid contents. The effect of epinephrine can be attributed to its interaction with alpha-adrenergic receptors, since the inhibition of glucuronide production by epinephrine was reversed by an alpha-antagonist (phentolamine) but not by a beta-antagonist, propranolol. Since alpha-adrenergic agonists increase the cytosolic free calcium concentration, we investigated the possibility that the decrease in glucuronide production elicited by epinephrine was mediated by calcium. Removal of calcium from the perfusion fluid diminished the inhibition of glucuronide production by epinephrine, while increasing extracellular calcium from 0 to 150 microM restored the inhibition in a dose-dependent manner. In the presence of extracellular calcium, glucuronide production was inhibited by the addition of the calcium ionophore A23187 or angiotensin II, a hormone which increases cytosolic calcium. Concentrations of ionized calcium comparable to physiological intracellular levels (0.1-2 microM) increased microsomal beta-glucuronidase activity by 50 to 100% but had no effect on microsomal glucuronosyl-transferases . These results indicate that activation of hepatic alpha-adrenergic receptors increases cytosolic calcium which stimulates microsomal beta-glucuronidase activity. This decreases net glucuronide formation by the liver. In support of this hypothesis, rates of glucuronide production were unaffected by epinephrine in perfused livers from beta-glucuronidase-deficient C3H/HeJ mice.
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PMID:Calcium-mediated inhibition of glucuronide production by epinephrine in the perfused rat liver. 633 73

Bilirubin monoglucuronide is rapidly deconjugated when incubated with UDP and rat liver microsomal preparations at pH 5.1. The following evidence was found that this reaction is catalyzed by UDP-glucuronyltransferase: (i) unconjugated bilirubin and UDP-glucuronic acid were identified as the reaction products; (ii) Gunn rat microsomal preparations lack bilirubin UDP-glucuronyltransferase deficiency and do not catalyze the deconjugation reaction, and (iii) neither saccharo-1,4-lactone, a beta-glucuronidase inhibitor, nor butylated hydroxytoluene, an inhibitor of spontaneous isomerisation, affect the rate of the deconjugation reaction. Deconjugation appears to be the reverse of UDP-glucuronyltransferase-catalyzed glucuronidation. The conditions for the reverse reaction differ in the following aspects from those of the forward reaction: (i) nucleotide triphosphates stimulate the reverse reaction probably allosterically; (ii) UDP-N-acetylglucosamine stimulates the forward reaction but has no effect on the reverse reaction; (iii) the optimal pH for the reverse reaction is pH 5.1 and for the forward reaction is pH 7.8, and (iv) Mg++ ion is not required for the reverse reaction but stimulates the forward reaction. Detergents stimulate both reactions. Stimulation of the reverse reaction by nucleotide triphosphates and detergents is mutually independent and additive which suggests different mechanisms of action. Deconjugation reactions may become important during parenchymatous liver disease when, as a result of anaerobic glycolysis, intracellular pH decreases. Elevated levels of unconjugated bilirubin in the serum of patients with parenchymatous liver disease may be a sign of sick liver cells rather than decreased UDP-glucuronyltransferase activity.
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PMID:UDP-glucuronyltransferase-catalyzed deconjugation of bilirubin monoglucuronide. 643 92

1. Cutaneous UDP-glucuronosyltransferase activity (E.C.2.4.1.17) was demonstrated in rat- and hairless mouse-skin microsomes using 1-naphthol as substrate. 2. Addition of the detergent Brij 35 increased the activity by approximately twofold in both species. 3. Inhibitor studies demonstrated that under the assay conditions used any UDP-glucuronic acid pyrophosphatase or beta-glucuronidase present did not interfere with the conjugation reaction. 4. Substrate inhibition was observed in hairless mouse-skin preparations and biphasic response to increasing naphthol concentration was seen in rat-skin microsomes. 5. The apparent Km values were considerably lower than those reported for liver. The sp. activity (per mg microsomal protein) in unactivated rat-skin microsomes was about 50% of that reported in unactivated rat-liver microsomes. 6. Pretreatment with 3-methylcholanthrene resulted in a small increase in cutaneous UDP-glucuronosyltransferase activities in both species.
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PMID:UDP-glucuronosyltransferase activity in rat-and hairless mouse skin-microsomes. 681 5

A rapid and sensitive radioassay for measuring UDP-glucuronosyltransferase activities (EC 2.4.1.17) toward the major endogenous substrates hyodeoxycholic and hyocholic acids, bilirubin, estriol, androsterone, and testosterone has been developed. In this assay, 14C-labeled glucuronides are formed from the enzyme-catalyzed reaction of 14C-labeled UDP-glucuronic acid with the unlabeled aglycones. Following incubation, the 14C-labeled glucuronides are separated under acidic conditions from the unreacted 14C-labeled UDP-glucuronic acid by a single extraction with ethyl acetate. The recovery of glucuronides into ethyl acetate was greater than 90%, whereas the carryover of unreacted UDP-glucuronic acid into the organic phase was approximately 0.2%. The reaction products extracted into ethyl acetate were characterized by their mobilities in thin-layer chromatography and identified as glucuronides by their sensitivity to hydrolysis with beta-glucuronidase and inhibition of hydrolysis by the specific beta-glucuronidase inhibitor D-saccharic acid-1,4-lactone. The optimal conditions of enzyme reactions with the individual aglycones have been defined with human liver microsomes as enzyme source. For all aglycones investigated, 10-30 micrograms of microsomal protein are sufficient for enzyme estimation. The assay is applicable to biochemical studies of UDP-glucuronosyltransferases, as well as to measurement of these enzyme activities from small amounts of clinical liver specimens.
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PMID:Radioassay of UDP-glucuronosyltransferase activities toward endogenous substrates using labeled UDP-glucuronic acid and an organic solvent extraction procedure. 808 74

The effects of detergent, alamethicin (a channel-forming peptide), and the inducers phenobarbital and 3-methylcholanthrene on glucuronidation of all-trans-retinoic acid (atRA) and 5,6-epoxy-atRA have been investigated using liver microsomes from Sprague-Dawley and Fischer 344 rats. Conditions for enzymatic glucuronidation were optimized for substrate concentration, protein, and time by using atRA and Sprague-Dawley microsomes. With detergent-activated Sprague-Dawley microsomes, 5,6-epoxy-atRA was shown to be a significantly better substrate than atRA for microsomal glucuronidation (263 vs. 116 pmol/mg/min for 5,6-epoxy-atRA and atRA, respectively). The product of incubation of microsomes with atRA and UDP-glucuronic acid was identified as a glucuronide by beta-glucuronidase hydrolysis and by HPLC analysis. Alamethicin was shown to be a highly effective activator of glucuronidation activity; atRA and 5,6-epoxy-atRA glucuronidation rates were increased 2- and 3-fold, respectively, compared with detergent activation. Alamethicin (but not detergent) significantly increased retinoid glucuronidation by microsomes from Fischer 344 rats treated with phenobarbital and 3-methylcholanthrene, compared with untreated controls. The two compounds were equally effective inducers of activity, although 5,6-epoxy-atRA was again the better substrate. The same control and induced Fischer rat microsomes were photolabeled with [32P]5-azido-UDP-glucuronic acid in the absence or presence of detergent, two concentrations of alamethicin, and a 10-fold molar excess of unlabeled UDP-glucuronic acid. Photoincorporation into microsomal proteins from detergent-disrupted induced microsomes was 2-3 times greater than that of controls. Alamethicin increased photoincorporation of the probe into UDP-glucuronosyltransferase proteins an additional 1.5-2-fold in control and induced microsomes, compared with the respective detergent-activated samples.
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PMID:Glucuronidation of all-trans-retinoic acid and 5,6-epoxy-all-trans-retinoic acid. Activation of rat liver microsomal UDP-glucuronosyltransferase activity by alamethicin. 901 Jun 23


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