Browse
Submit Data
Databases
API
Help

Dataset Information

0 Views

0 Connections

0 Citations

0 Reanalyses

0 Downloads

Omics score: 0

Effect on uridine diphosphate glucuronyltransferase activity of depleting and restoring phospholipids to guinea-pig liver microsomal preparations.

ABSTRACT: Phospholipid depletion substantially inhibited the maximum demonstrable activities of the forward (glucuronidation) and reverse reactions of UDP-glucuronyltransferase towards p-nitrophenol in guinea-pig liver microsomal preparations. Dispersions of liver phospholipids restored activity, whereas non-phospholipid amphipaths failed to do so effectively. These results suggest that the system is probably phospholipid-dependent rather than conformationally constrained by phospholipids.

SUBMITTER: Berry CS

PROVIDER: S-EPMC1172782 | biostudies-other | 1976 Mar

REPOSITORIES: biostudies-other

ACCESS DATA

Json Xml

Similar Datasets

The phospholipid-dependence of uridine diphosphate glucuronyltransferase. Phospholipid depletion and re-activation of guinea-pig liver microsomal enzyme.

Project description:More than 80% of the phospholipid component of guinea-pig liver microsomal membranes (prepared with 154mM-KCl) was removed by treatment with phospholipase A followed by extraction of the lysophosphatides and fatty acids produced with albumin. Delipidation strongly inactivated the highly active UDP-glucuronyltransferase of these preparations and activity was restored by mixtures of phosphatidylcholine and lysophosphatidylchlone. However, small quantities of lysophosphatides were still associated with the delipidated fractions after extraction with albumin and might have influenced the inactivation and re-activation observed. To eliminate these uncertainties, microsomal proteins and phospholipids were separated by gel filtration on Sephadex G-150 in the presence of cholate. This technique also strongly inactivated the enzyme but did not generate membrane-active phospholipid degradation products. High transferase activity was again restored to the delipidated protein by choline glycerophosphatides. These results confirm the view that the fully active form of microsomal UDP-glucuronyltransferase is phospholipid-dependent.

| S-EPMC1164666 | biostudies-other

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

Project description: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.

| S-EPMC1163909 | biostudies-other

Stimulation of microsomal uridine diphosphate glucuronyltransferase by glucuronic acid derivatives.

Project description:The glucuronic acid adducts of 1-naphthol, 2-naphthol and 4-methylumbelliferone activate microsomal UDP-glucuronyltransferase (EC 2.4.1.17) when the enzyme is assayed with p-nitrophenol as aglycone. Phenyl glucuronide and oestriol 3beta-glucuronide also activate UDP-glucuronyltransferase. but to a lesser extent. Activation by glucuronides is not dependent on metal ions, but is blocked by prior treatment of microsomal fractions with p-chloromercuribenzoate. The kinetic mechanism of activation is concluded to be an increase in the affinity of the enzyme for UDP-glucuronic acid. Activation by 1-naphthyl glucuronide, at high concentrations of p-nitrophenol, is not affected by 1-naphthol. Apparently 1-naphthyl glucuronide activates the preparation by binding at a site that is separate from the site of glucuronidation of 1-naphthol. Further evidence for the existence of distinct effector sites for the glucuronides was provided by the finding that activation by glucuronides is inhibited competitively by aglycone glucosides. These glucosides do not inhibit the rate of glucuronidation of p-nitrophenol in the absence of glucuronide adducts, nor do they alter the rate of glucuronidation of 1-naphthol. When UDP-glucuronyltransferase is assayed with 1-naphthol as aglycone it is activated by p-nitrophenyl glucuronide, 4-methyl-umbelliferyl glucuronide and under appropriate conditions by its own glucuronide. These activations are similarly inhibited by aglycone glucosides. p-Nitrophenyl glucuronide also stimulates the rate of glucuronidation of o-aminophenol, o-aminobenzoate and bilirubin.

| S-EPMC1166273 | biostudies-other

Properties of lubrol-extracted uridine diphosphate glucuronyltransferase.

Project description:1. A partially purified UDP-glucuronyltransferase was obtained by extracting rat liver microsomal preparations with Lubrol, a non-ionic detergent. 2. The soluble enzyme catalysed conjugation of both o-aminophenol and p-nitrophenol and was extremely stable when compared with untreated microsomal preparations. 3. The characteristics of the conjugation of the two phenols were found to differ with respect to pH optimum, bivalent cation requirement and Michaelis constants, suggesting that more than one enzyme is involved in the conjugation reaction.

| S-EPMC1178261 | biostudies-other

The phospholipid-dependence of uridine diphosphate glucuronyltransferase. Temperature-dependence of microsomal enzyme activity (reverse reaction).

Project description:Arrhenius plots of the non-latent UDP-glucuronlytransferase reverse reaction (p-nitrophenyl glucuronide donor) activity of guinea-pig microsomal membranes prepared with 15 mM-KCl were linear from 5 to 40 degrees C. These plots for other preparations from guinea-pig and rat liver (i.e. preparations that show transferase latency) exhibited two linear regions intersecting at a transition point near 19--21 degrees C. This discontinuity was abolished when latency was removed by treating the membranes with perturbants of phospholipid-bilayer structure. Thus the temperature-depdendnces of the reverse reaction catalysed by the enzymes of these various preparations are similar to those of the corresponding forward reactions [Pechey, Graham & Wood (1978) Biochem. J. 175, 115--1124]. Perturbants activated the enzyme of KCl-prepared guinea-pig microsomal membranes only slightly and caused no significant alteration to Arrhenius plots of its forward or reverse reaction activities. These results support the 'compartmentation' theory of UDP-glucuronyltransferase lactency.

| S-EPMC1161381 | biostudies-other

The phospholipid-dependence of uridine diphosphate glucuronyltransferase. Reactivation of phospholipase A-inactivated enzyme by phospholipids and detergents.

Project description:Specific degradation of the phospholipid membrane of guinea-pig liver microsomal fraction with phospholipase A inactivated glucuronyltransferase. The inactivation was reversed by phosphatidylcholine and mixed microsomal phospholipid micelles at concentrations similar to those present in intact microsomal preparations. The other commonly occurring phospholipids did not reactivate phospholipase A-treated enzyme. Since the mixed microsomal phospholipids consisted mainly of phosphatidylcholine, it is concluded that the reactivation by phospholipids is phosphatidylcholine-specific. Reactivation was also achieved by low concentrations of the cationic detergents cetylpyridinium chloride and cetyltrimethylammonium bromide. Higher concentrations of these detergents inactivated the glucuronyltransferase activity of intact and phospholipase A-treated microsomal fractions. Anionic detergents were potent inactivators of the glucuronyltransferase activity of untreated and phospholipase A-treated microsomal fractions, whereas non-ionic detergents had little effect on the activity of either preparation. Measurements of the zeta-potentials of the micellar species used in this study showed that no obvious relationship existed between the zeta-potentials and the ability to reactivate glucuronyltransferase. However, high positive or negative zeta-potentials were correlated with the ability of the amphipathic compound to inactivate glucuronyltransferase.

| S-EPMC1177088 | biostudies-other

The heterogeneity of uridine diphosphate glucuronyltransferase from rat liver.

Project description:1. The glucuronide conjugation of p-nitrophenol, phenolphthalein, o-aminophenol and 4-methylumbelliferone by rat liver microsomes has been studied. The detergent Triton X-100 activated UDP-glucuronyltransferase activity towards all these substrates, therefore the optimum activating concentration was added in all experiments. 2. Mg(2+) enhanced the conjugation of the substrates. 3. With phenolphthalein substrate inhibition occurred but this could be relieved by adding albumin, which binds excess of phenolphthalein. 4. Kinetic constants of the substrates and UDP-glucuronate have been determined. Mutual inhibition was found with the substrates p-nitrophenol, 4-methylumbelliferone and phenolphthalein. p-Nitrophenol conjugation was inhibited competitively by phenolphthalein and 4-methylumbelliferone. 5. o-Aminophenol did not inhibit the conjugation of the other three substrates because these are conjugated preferentially to o-aminophenol. 6. It is concluded that the four substrates are conjugated by one enzyme at the same active site.

| S-EPMC1178020 | biostudies-other

Studies on the purification of rat liver uridine diphosphate glucuronyltransferase.

Project description:1. A stable, more highly purified, preparation of UDP-glucuronyltransferase was obtained than previously reported. 2. Enzyme activity towards o-aminophenyl and p-nitrophenyl was increased 43- and 46-fold respectively. 3. The final preparation contains only three staining polypeptide bands visible after sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. 4. The only known major accompanying protein appears to be epoxide hydratase. 5. The purified enzyme activity towards o-aminophenol can still be activated 3 fold by diethylnitrosamine. 6. On evidence from purification, o-aminophenol and p-nitrophenol appear to be glucuronidated by the same enzyme protein. The possible recognition of the UDP-glucuronyltransferase enzyme is discussed.

| S-EPMC1164539 | biostudies-other

The phospholipid-dependence of uridine diphosphate glucuronyltransferase. Temperature-dependence of microsomal enzyme activity and thermotropic changes in membrane structure.

Project description:Arrhenius plots of the non-latent UDP-glucuronyltransferase (p-nitrophenol acceptor) activity of guinea-pig microsomal membranes prepared with 154 mM-KCl were linear from 5 to 40 degrees C. Arrhenius plots for other microsomal preparations from guinea pig and rat liver that show various degrees of transferase latency, exhibited two linear regions intersecting at a sharp transition point near 20-25 degrees C. This discontinuity was abolished or greatly decreased when transferase latency was removed by treating the membranes with perturbants of phospholipid bilayer strucutre. The fluorescent probe N-phenyl-1-naphthyl-amine detected a thermotropic change in the fluidity of the phospholipid acyl chains of all the microsomal membrane preparations studied, at temperatures close to those of the Arrhenius-plot transitions. It is concluded that the thermotropic change in the structure of the membrane bilayer probably is a 'phase separation' or clustering of phospholipids, which affects a permeability barrier that restricts access of substrate to the transferase molecules.

| S-EPMC1186046 | biostudies-other

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

Project description: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.

| S-EPMC1179372 | biostudies-other

OmicsDI is part of the ELIXIR infrastructure

OmicsDI is an Elixir interoperability service. Learn more ›

Tweets

OmicsDI Databases

PRIDE
PeptideAtlas
MassIVE
JPOST Repository
Physiome Model Repository

EGA
EVA
ENA
LINCS
PAXDB
Cell Collective

MetaboLights
Metabolomics Workbench
MetabolomeExpress
GNPS
BioModels
FAIRDOMHub

ArrayExpress
dbGaP
ExpressionAtlas
GEO
NODE

Information

Databases
Help
API
Contact us
Code on GitHub
Terms of use
Submit Data