1
|
Abstract
BACKGROUND & AIMS The contribution of glucuronidation toward human drug metabolism is carried out by the Super gene family of UDP-glucuronosyltransferases (UGTs). Regulation of the human UGT1A locus is tissue specific, resulting in the unique expression of multiple hepatic and extrahepatic gene products. Studies were undertaken to examine UGT1A expression in human hepatic and colonic tissues. METHODS UGT1A messenger RNA, protein, catalytic activity, and substrate kinetics were studied in 5 samples of normal hepatic and sigmoid colon tissue using duplex reverse-transcription polymerase chain reaction (RT-PCR), enzymatic and Western blot analysis, and indirect immunofluorescence analysis. RESULTS Specific patterns of UGT1A gene expression occur in the liver and colon, which were consistent with different banding patterns as detected by Western blot analysis using a UGT1A-specific antibody. However, microsomal UGT activities in colon were up to 96-fold lower for many phenolic substrates, a finding that was not concordant with RT-PCR and Western blot analysis. Interestingly, UGT activity toward tertiary amines and some steroid hormones was equal. CONCLUSIONS Differences of glucuronidation activity between human liver and colon suggest that UGT1A activity may be regulated as a result of the relative presence of individual isoforms with differing catalytic activities or by tissue-specific modulators after gene expression.
Collapse
Affiliation(s)
- C P Strassburg
- Department of Pharmacology and the Cancer Center, University of California, San Diego, La Jolla, California 92093-0636, USA
| | | | | | | |
Collapse
|
2
|
Yamashita A, Nagatsuka T, Watanabe M, Kondo H, Sugiura T, Waku K. Inhibition of UDP-glucuronosyltransferase activity by fatty acyl-CoA. Kinetic studies and structure-activity relationship. Biochem Pharmacol 1997; 53:561-70. [PMID: 9105408 DOI: 10.1016/s0006-2952(96)00793-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
We previously identified and purified UDP-glucuronosyltransferase (UGT) isoforms as targets of protein acylation from rat liver microsomes (Yamashita et al., Biochem J 312: 301-308, 1995). The acylation of UGT isoforms occurred upon incubation with acyl-CoA without another protein acyltransferase, suggesting that it was autoacylation. The study revealed the interaction of UGT isoforms with acyl-CoA. In the present study, the effects of fatty acyl-CoA on UGT activities were examined thoroughly, using a rat liver microsomal and purified enzyme fractions. The UGT activities of both fractions were inhibited by acyl-CoA in a concentration-dependent manner. The effect of acyl-CoA was observed on the activities toward various substrates, suggesting that the effect shows the wide spectrum of the isoforms of UGT. To assess the mechanism underlying the inhibition of UGT activity by acyl-CoA, the relationship of the inhibition, acyl-CoA binding to the proteins, and changes in the tertiary structure of the enzyme were examined. The kinetics of these phenomena were related closely with each other. Furthermore, the inhibition of UGT activity was specified for acyl-CoA, though a structurally related compound, acyl-3-dephosphoCoA, had no inhibitory effect. The results suggested that the specific binding of acyl-CoA to UGT isoforms induced conformational changes of the enzymes and resultant inhibition of UGT activity.
Collapse
Affiliation(s)
- A Yamashita
- Faculty of Pharmaceutical Sciences, Teikyo University, Kanagawa, Japan
| | | | | | | | | | | |
Collapse
|
3
|
Ouviña CB, Pavese CB, Lemberg A, Bengochea LA. Liver microsomal phospholipid fatty acids behavior and its relationship to bilirubin UDP-glucuronyltransferase activity in bile duct ligated rats. Arch Physiol Biochem 1995; 103:442-4. [PMID: 8548480 DOI: 10.3109/13813459509047136] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Phospholipid fatty acid composition and bilirubin UDP-glucuronyltransferase activity from liver microsomal membrane were studied in normal and in bile duct ligated rats. Incubation of normal microsomes with 15 microM bilirubin (considered as physiological concentration) yielded 60% bilirubin diglucuronide; in 2 days post-cholestatic rats, they showed 20% bilirubin diglucuronide which was undetectable in 8 days post-cholestatic group. When compared to controls, after 2 days of cholestasis, microsomal phospholipids showed a clear decrease in linoleic and arachidonic acids and an increment in palmitic and stearic acids. 8 days post-cholestatic rats presented a marked increase in palmitic, oleic and docosaexaenoic acids, while linoleic and arachidonic acids decreased. Cholestasis produced disturbances in microsomal phospholipids fatty acid composition; but these changes are unable to explain entirely the severe damage observed in bilirubin diglucuronide formation.
Collapse
Affiliation(s)
- C B Ouviña
- Cátedra de Fisiopatología, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Argentina
| | | | | | | |
Collapse
|
4
|
Bock KW. UDP-glucuronosyltransferases and their role in metabolism and disposition of carcinogens. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 1994; 27:367-83. [PMID: 8068559 DOI: 10.1016/s1054-3589(08)61039-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- K W Bock
- Institute of Toxicology, University of Tübingen, Germany
| |
Collapse
|
5
|
Lear L, Nation RL, Stupans I. Effects of cyclophosphamide and adriamycin on rat hepatic microsomal glucuronidation and lipid peroxidation. Biochem Pharmacol 1992; 44:747-53. [PMID: 1510722 DOI: 10.1016/0006-2952(92)90412-c] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The effect of cytotoxic drug administration, as a single dose i.p. to rats (six rats/treatment group), on hepatic microsomal UDP-glucuronosyltransferase (UGT) activity was investigated. Glucuronidation of morphine in microsomes from control rats apparently involved at least two enzymes. Administration of cyclophosphamide (CP; 200 mg/kg 7 days prior to killing) significantly increased the rate of morphine glucuronidation over the range 0.05-10 mM, and significantly increased the apparent Vmax for the high capacity isoenzyme from 1.25 +/- 0.12 to 1.95 +/- 0.39 nmol/mg/min. In contrast, the activity of 1-naphthol UGT was not significantly altered by administration of CP. Rats treated with the same dose of CP 1 day prior to killing showed a significant decrease in microsomal morphine-UGT activity at 0.05 and 2.5 mM morphine, but a significant increase in activity was observed following administration of CP or Adriamycin (AD; 10 mg/kg) 4 days prior to killing. The extent of microsomal lipid peroxidation was significantly increased in microsomes obtained from rats treated with CP or AD 4 days prior to killing, and was positively correlated (P less than 0.001) with the rate of glucuronidation of 0.05 and 2.5 mM morphine. Preincubation of microsomes in the presence of CP (5 mM) and AD (100 microM) significantly decreased the rate of glucuronidation of 2.5 mM morphine. In vitro NADPH-mediated lipid peroxidation significantly increased the activity of both the high and low affinity morphine-UGT isoenzymes. Administration of the cytotoxic drugs CP and AD may alter microsomal morphine-UGT activity via the process of lipid peroxidation, although other mechanisms cannot be excluded.
Collapse
Affiliation(s)
- L Lear
- School of Pharmacy, University of South Australia, Adelaide
| | | | | |
Collapse
|
6
|
Bengochea LA, Ouviña GB, Pavese A, Lemberg A. Changes in microsomal phospholipid fatty acids composition in cholestatic rats. ARCHIVES INTERNATIONALES DE PHYSIOLOGIE, DE BIOCHIMIE ET DE BIOPHYSIQUE 1992; 100:109-11. [PMID: 1379485 DOI: 10.3109/13813459209035271] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
In the rat, the effect of the bile duct ligation on liver microsomal phospholipid fatty acid composition and on phosphatidylcholine, phosphatidylserine and phosphatidylinositol pattern were studied. After two days of cholestasis, microsomal phospholipid fatty acids showed a decrease in linoleic, stearic and arachidonic acids and an increase in oleic and docosahexaenoic ones, as compared to controls. Phosphatidylcholine showed an increment in oleic and palmitic acid content and a concomitant decrease in arachidonic acid. Phosphatidylserine showed a progressive increase while phosphatidylinositol showed a progressive decrease in all fatty acids. Eight-days post-cholestatic rats showed a marked increase in oleic acid, whereas linoleic, arachidonic, stearic and palmitic acids concentration decreased. Phosphatidylcholine showed a global decrease in its fatty acid content, except for oleic which is increased. Phosphatidylserine showed an increase over the two-days cholestasis fatty acids values. Phosphatidylinositol decreased in most fatty acids except in docosahexaenoic acid that recovered normal values. It was concluded that cholestasis produced significative changes in the fatty acid composition of the major phospholipids constituents of the microsomal membranes.
Collapse
Affiliation(s)
- L A Bengochea
- Cátedra de Fisiopatología, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires
| | | | | | | |
Collapse
|
7
|
Lear L, Nation RL, Stupans I. Influence of morphine concentration on detergent activation of rat liver morphine-UDP-glucuronosyltransferase. Biochem Pharmacol 1991; 42 Suppl:S55-60. [PMID: 1768286 DOI: 10.1016/0006-2952(91)90392-i] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The effect of two detergents, Triton X-100 and Brij 58, on the production rate of morphine-3-glucuronide by rat hepatic microsomes has been investigated over a range of detergent and substrate concentrations, using a specific HPLC assay. Activation of morphine-UDP-glucuronosyltransferase (morphine-UDPGT) by Triton X-100 was more complex than that shown by Brij 58. At the optimal concentration of Triton X-100 (0.1-0.125 mg Triton X-100/mg microsomal protein), relative metabolic activity (activity of morphine-UDPGT in the activated state/activity of morphine-UDPGT in the native state; RMA) was 0.9, 1.3 and 2.5 at morphine concentrations of 0.05, 0.5 and 2.5 mM, respectively. Analysis of results from six individual rats in the native and maximally activated state (0.125 mg Triton X-100/mg microsomal protein) showed that RMA was highly dependent upon substrate concentration (P less than 0.0001). Activation produced by the optimal concentration of Brij 58 (0.15 mg Brij 58/mg microsomal protein) was also dependent upon substrate concentration with values for RMA of 3.3, 6.4 and 9.3 at morphine concentrations of 0.05, 0.5 and 2.5 mM, respectively. Analysis of kinetic data is complicated by substrate concentration-dependent detergent activation. It is proposed that factors contributing to substrate concentration-dependent variable activation may include micellar solubilization of substrate by detergent and/or the presence of at least two enzyme forms capable of glucuronidating morphine with differential effects of detergents on these forms.
Collapse
Affiliation(s)
- L Lear
- School of Pharmacy, University of South Australia, Adelaide
| | | | | |
Collapse
|
8
|
Nakaoka M. Kinetic characteristics of UDP-glucuronosyltransferases towards a dithiol metabolite of malotilate in hepatic microsomes of rats and rabbits. Xenobiotica 1990; 20:619-27. [PMID: 2120856 DOI: 10.3109/00498259009046877] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
1. The kinetic activity of UDP-glucuronosyltransferases (UDPGT) towards a dithiol metabolite of malotilate, 2,2-di(isopropoxycarbonyl)ethylene-1,1-dithiol, was investigated using rat and rabbit hepatic microsomes. The thio-glucuronide formed was analysed by h.p.l.c. The Km values obtained using rat and rabbit UDPGT were 36.3 +/- 3.3 and 443 +/- 43 microM, respectively. The Vmax values were 7.14 +/- 0.61 and 29.2 +/- 6.4 nmol/min per mg (mean +/- SD, n = 3). 2. Phenobarbital, an inducer of the GT2 isoform of UDPGT, increased rat microsomal UDPGT activity towards the dithiol. In inhibitory studies, menthol and borneol (specific substrates for GT2a isoform) competitively inhibited glucuronidation of the dithiol. Thus it was concluded that formation of the thio-glucuronide was catalysed mainly by the GT2a isozyme of UDPGT, which is involved in glucuronidation of monoterpenoid alcohols.
Collapse
Affiliation(s)
- M Nakaoka
- Research Institute, Daiichi Pharmaceutical Co. Ltd, Tokyo, Japan
| |
Collapse
|
9
|
Bengochea L, Ouviña G, Sozzani P, Lemberg A. Protein and lipid disturbances in rat liver microsomal membranes after bile duct ligation. Biochem Biophys Res Commun 1987; 144:980-5. [PMID: 3579951 DOI: 10.1016/s0006-291x(87)80060-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
An analysis of proteins, phospholipids and cholesterol from liver microsomal membranes was performed in normal and post-cholestatic rats. Bile duct ligated rats showed a progressive decrease of these membrane constituents. Minor changes in peptide analysis, a marked decrease of phosphatidylcholine and phosphatidylinositol, disappearance of phosphatidylethanolamine and sphingomyelin, and a clear increment of phosphatidylserine was observed in post-cholestatic as compared to normal group. It was concluded that extra-hepatic cholestasis produces structural changes on the liver microsomes, particularly on phospholipid profile.
Collapse
|
10
|
Boutin JA. Indirect evidences of UDP-glucuronosyltransferase heterogeneity: how can it help purification? Drug Metab Rev 1987; 18:517-51. [PMID: 3131095 DOI: 10.3109/03602538708994131] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Affiliation(s)
- J A Boutin
- Institut de Recherches Servier, Suresnes, France
| |
Collapse
|
11
|
Armstrong RN. Enzyme-catalyzed detoxication reactions: mechanisms and stereochemistry. CRC CRITICAL REVIEWS IN BIOCHEMISTRY 1987; 22:39-88. [PMID: 3115676 DOI: 10.3109/10409238709082547] [Citation(s) in RCA: 106] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Enzyme catalyzed detoxication reactions are one of the primary defenses organisms have against chemical insult. This article reviews current chemical approaches to understanding the cooperative role of enzymes in the metabolism of foreign compounds. Emphasis is placed on chemical and stereochemical studies which help elucidate the mechanism of action and active-site topologies of the detoxication enzymes. The stereoselectivity of the cytochromes P-450 and flavin containing monooxygenases as well as the role of hemoglobin and lipid peroxidation in the primary metabolism of xenobiotics is discussed. Current knowledge of the mechanism and stereoselectivity of epoxide hydrolase is also presented. Three enzymes involved in secondary metabolism of xenobiotics, UDP-glucuronosyltransferase, sulfotransferase and glutathione S-transferase are discussed with particular emphasis on active site topology and cooperative participation with the enzymes of primary metabolism.
Collapse
Affiliation(s)
- R N Armstrong
- Department of Chemistry and Biochemistry, University of Maryland, College Park
| |
Collapse
|
12
|
Boutin JA, Antoine B, Fournel S, Siest G. Heterogeneity of hepatic microsomal UDP-glucuronosyltransferases activities: use and comparison of differential inductions in some mammalian species. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. B, COMPARATIVE BIOCHEMISTRY 1987; 87:513-22. [PMID: 3113821 DOI: 10.1016/0305-0491(87)90046-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
1. The co-injection in rats of the inducers 3-methylcholanthrene or phenobarbital and of a protein synthesis inhibitor (cycloheximide) shows that two clusters of hepatic UDP-Glucuronosyltransferases (GT1 and GT2) are under separate genomic expression and differentially regulated. 2. The administration of cycloheximide alone even suggests a distinct turn-over for these two groups of isoenzymes. 3. Indirect evidence for a UDPGT isoform specialized for some structurally-related exogenous substrates, the monoterpenoid alcohols, is brought. Their conjugation exhibits a small deficiency and a marked response to phenobarbital treatment in the Gunn rat and an exclusive inducibility by phenobarbital in the guinea-pig.
Collapse
|
13
|
Meredith CG, Muhoberac BB, Gray JP, Speeg KV, Dunn D, Hoyumpa AM, Schenker S. Hepatic oxidative drug metabolism and the microsomal milieu in a rat model of congenital hyperbilirubinemia. Biochem Pharmacol 1986; 35:3831-7. [PMID: 3778508 DOI: 10.1016/0006-2952(86)90672-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The aims of this study were to evaluate the hypothesis that impaired glucuronidation of bilirubin and possibly of drug oxidation in the liver of homozygous (jj) Gunn rats may be due to an altered microsomal milieu. Accordingly, we investigated and compared in vivo and in vitro demethylation of aminopyrine, hepatic cytochrome P-450 levels, microsomal lipid composition, and microsomal membrane fluidity in icteric, homozygous (jj) Gunn rats and in their anicteric heterozygous (jJ) littermates. In both males and females, [14C]aminopyrine demethylation in vivo, using the 14CO2 breath test, was unimpaired in the icteric animals. Likewise, cytochrome P-450 levels in the icteric and nonicteric groups were similar, and aminopyrine kinetics in vitro in the females were comparable in icteric and nonicteric littermates. The main lipid classes were also similar in the homozygous and heterozygous female Gunn rats, whereas only minor changes were seen in the phospholipid fatty acyl composition with a small, but significant, increase in the unsaturated index in the icteric group. Despite this, there was no apparent effect on hepatic microsomal membrane fluidity as measured by the order parameter of I[12,3] and the rotational correlation time of I[1,14] in either female or male sets of homozygous and heterozygous Gunn rats. Our data, therefore, do not support an alteration of composition or fluidity of the microsomal milieu as a mechanism of impaired bilirubin glucuronidation and possibly of oxidation in these animals. They also absolve long-term unconjugated hyperbilirubinemia as a mechanism of hepatic microsomal dysfunction. Our study, therefore, indirectly suggests that abnormal glucuronidation of bilirubin and some other aglycones in homozygous Gunn rats is due to genetic abnormalities involving the enzyme(s) itself.
Collapse
|
14
|
Boutin JA. Inhibition of microsomal NAD(P)H oxidation by Triton X-100. JOURNAL OF BIOCHEMICAL AND BIOPHYSICAL METHODS 1986; 13:171-8. [PMID: 3465799 DOI: 10.1016/0165-022x(86)90090-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The non-ionic detergent Triton X-100 is shown to inhibit the spontaneous oxidation of NAD(P)H associated with rat liver microsomes. Advantage of this observation is taken to measure different microsomal NAD(P)H-dependent oxidoreductase activities such as 3-alpha-hydroxysteroid dehydrogenase, dihydrodiol dehydrogenase and various xenobiotic oxidoreductases. This inhibition provides an easy method for the screening of the under-investigated microsomal oxidoreductive metabolism of xenobiotics.
Collapse
|
15
|
Wang LH, Zakim D, Rudolph AM, Benet LZ. Developmental alterations in hepatic UDP-glucuronosyltransferase. A comparison of the kinetic properties of enzymes from adult sheep and fetal lambs. Biochem Pharmacol 1986; 35:3065-70. [PMID: 3092831 DOI: 10.1016/0006-2952(86)90387-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The kinetic properties of hepatic microsomal UDP-glucuronosyltransferase were studied in sheep in the perinatal period, using acetaminophen as the aglycone. Kinetic analyses indicated that activity at Vmax was significantly less in fetal microsomes (113, 135 or 141 days) as compared with the adult sheep. However, these differences between fetal and adult animals were not due simply to smaller amounts of UDP-glucuronosyltransferases catalyzing conjugation of acetaminophen in fetuses versus adults. Thus, the kinetic properties of UDP-glucuronosyltransferase(s) were different in fetus and adult. The "fetal" versus "adult" enzyme had a higher affinity for UDP-glucuronic acid, but a poorer affinity for acetaminophen. Furthermore, enzyme in fetal liver (113 days of gestation) was activated about 30% by the allosteric effector UDP-N-acetylglucosamine, whereas enzyme in adult liver was activated by 500%. These differences between fetal and adult enzymes diminished just prior to parturition (141-day fetus). Enzyme in microsomes from the 141-day fetus responded to UDP-N-acetylglucosamine-like enzyme in adult microsomes and had affinities for substrates that were similar to "adult" enzymes. These data indicate that maturation of the system that glucuronidates acetaminophen is a complex process. It may involve the expression in fetuses of a type of UDP-glucuronosyltransferase that is different from that expressed in the adult. An alternative but not mutually exclusive possibility is that maturation of the glucuronidation system involves modification of enzyme function by alteration of the phospholipids in the immediate environment of UDP-glucuronosyltransferase within the microsomal membrane.
Collapse
|
16
|
Falany CN, Green MD, Swain E, Tephly TR. Substrate specificity and characterization of rat liver p-nitrophenol, 3 alpha-hydroxysteroid and 17 beta-hydroxysteroid UDP-glucuronosyltransferases. Biochem J 1986; 238:65-73. [PMID: 3099767 PMCID: PMC1147098 DOI: 10.1042/bj2380065] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Purified preparations of rat liver 17-hydroxysteroid, 3-hydroxyandrogen and p-nitrophenol (3-methylcholanthrene-inducible) UDP-glucuronosyltransferases were further characterized as to their substrate specificities, phospholipid-dependency and physical properties. The two steroid UDP-glucuronosyltransferases were shown to exhibit strict stereospecificity with respect to the conjugation of steroids and bile acids. These enzymes have been renamed 17 beta-hydroxysteroid and 3 alpha-hydroxysteroid UDP-glucuronosyltransferase to reflect this specificity for important endogenous substrates. An endogenous substrate has not yet been identified for the p-nitrophenol (3-methylcholanthrene-inducible) UDP-glucuronosyltransferase. The steroid UDP-glucuronosyltransferase activities were dependent on phospholipid for maximal catalytic activity. Complete delipidation rendered the UDP-glucuronosyltransferases inactive, and enzymic activity was not restored when phospholipid was added to the reaction mixture. After partial delipidation, phosphatidylcholine was the most efficient phospholipid for restoration of enzymic activity. Partial delipidation also altered the kinetic parameters of the 3 alpha-hydroxysteroid UDP-glucuronosyltransferase. The three purified UDP-glucuronosyltransferases are separate and distinct proteins, with different amino acid compositions and peptide maps generated by limited proteolysis with Staphylococcus aureus V8 proteinase. Some similarity was observed between the amino acid composition and limited proteolytic maps of the steroid UDP-glucuronosyltransferases, suggesting they are more closely related to each other than to the p-nitrophenol UDP-glucuronosyltransferase.
Collapse
|
17
|
Castuma CE, Brenner RR. Effect of dietary cholesterol on microsomal membrane composition, dynamics and kinetic properties of UDPglucuronyl transferase. BIOCHIMICA ET BIOPHYSICA ACTA 1986; 855:231-42. [PMID: 3081026 DOI: 10.1016/0005-2736(86)90169-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The effect of cholesterol administration in vivo on the lipid composition, dynamic properties of the microsomal membrane of guinea pig livers and the kinetic properties of UDPglucuronyl transferase were studied. Cholesterol administration in the diet evoked an increase of microsomal cholesterol, but no significant changes in the fatty-acid composition of total lipids or of each phospholipid class. Instead, the phosphatidylethanolamine, phosphatidylcholine molar ratio of the membrane was markedly decreased from 0.57 to 0.38. This decline was not enough to counterbalance the overall 'ordering' effect of cholesterol and consequently, the fluorescence anisotropy of the membranes labeled with 1,6-diphenylhexatriene was increased. The lateral diffusion evaluated by measuring the pyrene excimer formation was decreased by the cholesterol incorporation. These physical changes were associated with changes in the kinetic properties of UDPglucuronyl transferase: Vmax increased, while the Km of the different steps of the reaction decreased in the modified microsomes. Furthermore, a shift of the non-michaelian kinetics to michaelian, equivalent to a decrease of a negative homotropic effect and apparent cooperativity of UDPglucuronic acid was observed since the Hill coefficient changed, approaching 1. A non-michaelian kinetics of this enzyme is an indication of boundary lipids in the gel phase and a shift to michaelian, a change of the surrounding lipids to a liquid-crystalline structure. In consequence, our results suggest that cholesterol incorporation in the microsomal membrane while producing a condensing effect of bulk lipids would produce an opposite effect on the UDPglucuronyl transferase boundary lipids.
Collapse
|
18
|
Thomassin J, Dragacci S, Faye B, Magdalou J, Siest G. Kinetic constant determination of liver microsomal and purified UDP-glucuronosyltransferase after phenobarbital and 3-methylcholanthrene treatments in rats. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. C, COMPARATIVE PHARMACOLOGY AND TOXICOLOGY 1986; 83:127-31. [PMID: 2869885 DOI: 10.1016/0742-8413(86)90024-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
After induction by phenobarbital and 3-methylcholanthrene, UDP-glucuronosyltransferase involved mainly in the conjugation of planar substrates was purified. Compared to the microsomal enzyme, the purified protein exhibited less affinity towards the substrates, but the corresponding Vmaxs were increased. These results were attributed to a change in the lipid environment of the purified enzyme. The conjugation rate for 4-hydroxycoumarine was 15-45 times less than that measured for the 7-hydroxyisomer with the microsomal or the purified enzymes. Immunoprecipitation studies of the enzyme revealed that the two compounds were transformed by the same enzyme, or metabolized by two separate enzymes presenting the same antigenic site. The orientation of the hydroxyl group of planar aglycones in the active site is the determinant for the efficiency of catalysis.
Collapse
|
19
|
Thomassin J, Boutin JA, Siest G. UDP-glucuronosyltransferase(s) activities towards natural substrates in rat liver microsomes. Kinetic properties and influence of triton X-100 activation. PHARMACOLOGICAL RESEARCH COMMUNICATIONS 1985; 17:1005-15. [PMID: 3937161 DOI: 10.1016/0031-6989(85)90107-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
We studied the in vitro capability of hepatic microsomal UDP-glucuronosyltransferase (UDPGT) in male rats to conjugate 22 natural xenobiotics which are known to be excreted as glucuronides in vivo. We clearly demonstrated that the Vmax can range in a decreasing scale for the following families of aglycones: 7-hydroxylated coumarins greater than 2-naphthol and phenols greater than monoterpenoid alcohols greater than 4-hydroxylated coumarins. The Km app. cannot be arranged in the same scale. This suggests that the catalytic mechanism of UDPGT is dependent on the hydroxyl group reactivity rather than on the binding interaction at the active site expressed by the Km app. The effects of various concentrations of detergent (Triton X-100) were determined on specificity (apparent Km) and activity (Vmax). For the 22 aglycones we showed that activation caused a variation in the Vmax which was a function of the concentration in detergent. The maximum of this activation did not always correspond to the same detergent/protein weight ratio. The impact of activation on Km app. was less clear since the variations observed were slightly different.
Collapse
|
20
|
Boutin JA, Thomassin J, Siest G, Cartier A. Heterogeneity of hepatic microsomal UDP-glucuronosyltransferase activities. Conjugations of phenolic and monoterpenoid aglycones in control and induced rats and guinea pigs. Biochem Pharmacol 1985; 34:2235-49. [PMID: 3925953 DOI: 10.1016/0006-2952(85)90777-4] [Citation(s) in RCA: 63] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
In this report we present evidence that the heterogeneity of hepatic microsomal UDP-glucuronosyltransferase(s) (UDPGT) activities depends on the chemical structures of the aglycones as well as their biophysical constants. Three animal models were used: Wistar rats, which have active UDPGTs; Gunn rats, in which some of the UDPGT activities are reduced, but which can be induced by phenobarbital; and guinea pigs. In Wistar rats, we found that some coumarins were poor substrates of UDPGT (GT1) and that twenty monoterpenoid alcohol activities showed typical phenobarbital-inducible behavior. In Gunn rats, we showed that substitution of the phenolic aglycone by bulky (alkyl- or methoxy-) groups in the 2-position of the phenolic ring decreased UDPGT (GT1) activity, whereas substitution in the 4-position resulted in an increase in this activity. We also showed that, in this particular strain, activities toward terpenes were less affected than activities toward flat (aromatic) aglycones. Induction by phenobarbital in Gunn rats increased the activity and limited the deficiency for monoterpenoid alcohols. In guinea pigs, we confirmed that phenobarbital selectively increased the activities of UDPGT towards twenty monoterpenoid alcohols without affecting other typical phenobarbital-induced activities such as those for conjugation of morphine. Finally, we showed that orientation of the aglycone molecule in the active site was apparently related to its dipole moment and that the distance between "acceptor-oxygen" (hydroxyl) and the carbons out of the general plane of the molecule was an important factor. These studies clearly suggest that rat and guinea pig contain a UDPGT(monoterpenoid alcohols) with restricted specificities and also that UDPGT(GT1) comprises at least two or three different isoenzymes, each with a slightly different restricted specificity towards flat aromatic aglycones.
Collapse
|
21
|
Serres-Guillaumond M, Broquet P, Louisot P. Modulation of solubilized brain fucosyltransferase activity by phospholipids. BIOCHIMICA ET BIOPHYSICA ACTA 1984; 794:104-9. [PMID: 6733122 DOI: 10.1016/0005-2760(84)90303-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Phospholipids interact on Triton X-100 solubilized GDP-fucose: asialofetuin fucosyltransferase (EC 2.4.1.68) isolated from sheep brain. This enzymatic activity is modulated by charged phospholipids. In particular, phosphatidic acid and analogues markedly inhibit the transfer of fucose from GDP-[14C]fucose. Kinetic studies show that phosphatidic acid interacts as a mixed inhibitor: the velocity and affinity of fucosyltransferase for the GDP-fucose and asialofetuin substrates are strongly decreased. However, this inhibitory effect is not related to stereospecificity, and the different parameters involved in the enzymatic reaction of glycosylation are not modified. The nature of fatty acids and chemical bond (ester or ether) occurring in the carbohydrate chain does not modify the behaviour of phosphatidic acid with respect to fucosyltransferase activity. Further, the physical state of phosphatidic acid (gel phase or liquid crystalline phase) has no influence. However, as the inhibition is closely pH-dependent, these data suggest that phosphatidic acid might directly interact with the active site of the enzyme and induce a conformational change.
Collapse
|
22
|
Cummings J, Graham AB, Wood GC. Kinetic studies of latent microsomal UDP-glucuronyltransferases. Kinetics of glucuronidation in intact and perturbant-treated membranes. BIOCHIMICA ET BIOPHYSICA ACTA 1984; 771:127-41. [PMID: 6422987 DOI: 10.1016/0005-2736(84)90525-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Double-reciprocal plots (with UDP-glucuronate as varied substrate) of the rate of glucuronidation of p-nitrophenol by the latent UDP-glucuronyltransferases of intact guinea pig and rat liver microsomal membranes (prepared with 154 mM KCl and 0.25 M sucrose) were continuously curved concave-downwards. Good fits to the kinetic data were obtained by using two different calculation methods which assume that two forms (high K and low K) of the transferase catalyse the reaction simultaneously. No evidence of cooperativity in binding of UDP-glucuronate to the enzyme was found. When latency of the enzymes of these preparations was destroyed by disrupting the membranes with Triton X-100 or lysophosphatidylcholine, double-reciprocal plots were linear. With guinea pig membranes, lysophosphatidylcholine generated an activated single-enzyme form obeying the simple Michaelis-Menten rate law; K for the activated species was close to that (K1) for the native low K form and its value of V was greater than the combined maximum velocities (V1 + V2) of the two forms in intact membranes. With rat membranes, both perturbants produced a single activated form also with V greater than (V1 + V2) and with K2 greater than K greater than K1. These results are discussed and are consistent with the view of transferase latency which envisages that there are two populations (buried and exposed) of enzyme molecules in intact microsomal membranes. The effects of membrane perturbants on the kinetic parameters of the two native transferase forms were assessed by accounting for the possibility that the reactivity of the buried transferase is controlled by the rate of transport of UDP-glucuronate across the membrane matrix. The data are compatible with a model which supposes that UDP-glucuronate gains access to the buried population by a process with the kinetic characteristics of a facilitated transport system.
Collapse
|
23
|
UDP-glucose: 1, 3-β-glucan synthase in potato tubers: Solubilization and activation by lipids. ACTA ACUST UNITED AC 1983. [DOI: 10.1016/0304-4211(83)90096-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
|
24
|
Yusuf HK, Pohlentz G, Schwarzmann G, Sandhoff K. Ganglioside biosynthesis in Golgi apparatus of rat liver. Stimulation by phosphatidylglycerol and inhibition by tunicamycin. EUROPEAN JOURNAL OF BIOCHEMISTRY 1983; 134:47-54. [PMID: 6861762 DOI: 10.1111/j.1432-1033.1983.tb07529.x] [Citation(s) in RCA: 61] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Golgi vesicles were isolated and purified from rat liver, in which the specific activities of glycosyltransferases (e.g. GM3:CMP-NeuAc sialyltransferase, GD3 synthase; GM3:UDP-GalNAc galactosaminyltransferase, GM2 synthase) were 50-60-times enriched relative to microsomes or total homogenate. Synthesis of gangliosides GM2 and GM1 in such Golgi vesicles is, in the absence of any detergents, stimulated 6-fold and 20-fold respectively by phosphatidylglycerol. Other phospholipids like phosphatidylethanolamine and phosphatidylserine are also significantly stimulatory. With 50 micrograms Golgi protein and 1 nmol UDP-GalNAc, optimal stimulation of GM2 synthase was obtained with 20 micrograms of phosphatidylglycerol and 7.5 nmol of the lipid acceptor GM3. Under the same experimental conditions this stimulation exceeds (by about 40%) that obtained with optimal amount (200 micrograms) of the detergent octylglucoside. Phosphatidylglycerol, on the other hand, has virtually no stimulatory activity on the synthesis of ganglioside GD3 either in the presence of Mg2+ or Mn2+, indicating that facilitation by phospholipid of GM3 transport into Golgi vesicles was not the basis of stimulation of GM2 synthesis. Tunicamycin inhibits the synthesis of gangliosides GM2 and GM1 in isolated Golgi vesicles, but only in the absence of detergents. In the presence of phosphatidylglycerol, GM2 synthesis, for example, was inhibited by 60% by 2 micrograms tunicamycin and more than 85% by 10 micrograms tunicamycin, per 50 micrograms Golgi membrane protein. The inhibition was stronger on GM1 synthesis: 85% with 2.5 micrograms of the antibiotic. The dependence on phosphatidylglycerol and the degree of inhibition by tunicamycin of the synthetic activities are strictly dependent on the intactness of the Golgi vesicles: both phenomena become increasingly less evident when the vesicles are pelleted, and frozen and thawed several times, and completely disappear when the vesicles are solubilized by detergents or disrupted by ultrasonication. Furthermore, tunicamycin inhibition is reversible by increased concentration of phosphatidylglycerol. All these results indicate that phosphatidylglycerol does not stimulate, and tunicamycin does not inhibit, the transferases themselves; rather, the two opposing effects might relate to carrier-mediated transport, e.g. of nucleotide sugars, across Golgi vesicles.
Collapse
|
25
|
|
26
|
Bock KW, Burchell B, Dutton GJ, Hänninen O, Mulder GJ, Owens IS, Siest G, Tephly TR. UDP-glucuronosyltransferase activities. Guidelines for consistent interim terminology and assay conditions. Biochem Pharmacol 1983; 32:953-5. [PMID: 6404284 DOI: 10.1016/0006-2952(83)90610-x] [Citation(s) in RCA: 169] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
|
27
|
Serres-Guillaumond M, Louisot P. Effect of phospholipids on membrane-bound and solubilized mannosyltransferase activity from aortic wall. THE INTERNATIONAL JOURNAL OF BIOCHEMISTRY 1983; 15:1313-20. [PMID: 6642052 DOI: 10.1016/0020-711x(83)90021-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Phospholipids interact on the membrane-bound and solubilized mannosyltransferase activity. The biosynthesis of Dol-P-Man is strongly inhibited by phosphatidic acid and lysophosphatidylcholine. The effect of phospholipids is not related to stereospecificity. Chemical properties of phospholipids (ester or ether bond, length of fatty acids and polarity of head groups) are not an essential factor for inhibition. The different parameters involved in enzymatic reaction of glycosylation are not modified by phospholipids, in particular the integrity of GDP-[14C]mannose. The inhibitory effect of lysophosphatidylcholine and phosphatidic acid on mannosyltransferase activities is related to their possible formation of micellar structures which definitely induce a conformation change of this enzyme.
Collapse
|