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Wilcox CS, Pearlman A. Chemistry and antihypertensive effects of tempol and other nitroxides. Pharmacol Rev 2009; 60:418-69. [PMID: 19112152 DOI: 10.1124/pr.108.000240] [Citation(s) in RCA: 280] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Nitroxides can undergo one- or two-electron reduction reactions to hydroxylamines or oxammonium cations, respectively, which themselves are interconvertible, thereby providing redox metabolic actions. 4-Hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (tempol) is the most extensively studied nitroxide. It is a cell membrane-permeable amphilite that dismutates superoxide catalytically, facilitates hydrogen peroxide metabolism by catalase-like actions, and limits formation of toxic hydroxyl radicals produced by Fenton reactions. It is broadly effective in detoxifying these reactive oxygen species in cell and animal studies. When administered intravenously to hypertensive rodent models, tempol caused rapid and reversible dose-dependent reductions in blood pressure in 22 of 26 studies. This was accompanied by vasodilation, increased nitric oxide activity, reduced sympathetic nervous system activity at central and peripheral sites, and enhanced potassium channel conductance in blood vessels and neurons. When administered orally or by infusion over days or weeks to hypertensive rodent models, it reduced blood pressure in 59 of 68 studies. This was accompanied by correction of salt sensitivity and endothelial dysfunction and reduced agonist-evoked oxidative stress and contractility of blood vessels, reduced renal vascular resistance, and increased renal tissue oxygen tension. Thus, tempol is broadly effective in reducing blood pressure, whether given by acute intravenous injection or by prolonged administration, in a wide range of rodent models of hypertension.
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Affiliation(s)
- Christopher S Wilcox
- Division of Nephrology and Hypertension, Kidney and Vascular Disorder Center, Georgetown University, Washington, DC 20007, USA.
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2
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Singhal SS, Yadav S, Roth C, Singhal J. RLIP76: A novel glutathione-conjugate and multi-drug transporter. Biochem Pharmacol 2008; 77:761-9. [PMID: 18983828 DOI: 10.1016/j.bcp.2008.10.006] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2008] [Revised: 10/01/2008] [Accepted: 10/02/2008] [Indexed: 11/17/2022]
Abstract
RLIP76, a stress-responsive, multi-functional protein with multi-specific transport activity towards glutathione-conjugates (GS-E) and chemotherapeutic agents, is frequently over-expressed in malignant cells. Our recent studies suggest that it plays a prominent anti-apoptotic role selectively in cancer cells. We have previously shown that RLIP76 accounts for up to 80% of the transport of GS-E and blocking the RLIP76-mediated transport of GS-E in cells results in the accumulation of pro-apoptotic endogenous electrophiles and on-set of apoptosis. Here we demonstrate that when RLIP76 mediate transport of GS-E is abrogated either by anti-RLIP76 IgG or accumulation of 4-hydroxynonenal (4-HNE) and its GSH-conjugate (GS-HNE) occurs and a massive apoptosis is observed in cells, indicate that the inhibition of RLIP76 transport activity at the cell surface is sufficient for observed anti-tumor activity. RLIP76 is linked with certain cellular functions including membrane plasticity and movement (as a primary 'effector' in the Ral pathway, perhaps functioning as a GTPase activating protein, or GAP), and as a component of clathrin-coated pit-mediated receptor-ligand endocytosis-a process that mediates movement of membrane vesicles.
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Affiliation(s)
- Sharad S Singhal
- Department of Molecular Biology and Immunology, University of North Texas Health Science Center, Fort Worth, TX 76107, USA.
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3
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Singhal SS, Wickramarachchi D, Singhal J, Yadav S, Awasthi YC, Awasthi S. Determinants of differential doxorubicin sensitivity between SCLC and NSCLC. FEBS Lett 2006; 580:2258-64. [PMID: 16579994 DOI: 10.1016/j.febslet.2006.03.038] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2005] [Revised: 03/06/2006] [Accepted: 03/08/2006] [Indexed: 11/18/2022]
Abstract
Doxorubicin (DOX) transport activity of Ral-interacting protein (RLIP76) in non-small cell lung cancer (NSCLC) is approximately twice that of in small cell lung cancer (SCLC). Since protein-kinase-C (PKC)alpha mediated phosphorylation of RLIP76 causes doubling of the specific activity of RLIP76, and NSCLC cells are known to have greater PKCalpha activity, we examined the contribution of PKC mediated phosphorylation of RLIP76 towards intrinsic DOX-resistance in human NSCLC. Expression of a deletion mutant RLIP76(delPKCalpha-sites) followed by depletion of the wild-type RLIP76 using a siRNA targeted at one of the deleted regions resulted in generation of cells expressing only the mutant protein, which could not be phosphorylated by PKCalpha. DOX-transport activity of the mutant RLIP76 purified from NSCLC and SCLC was similar and comparable to that of RLIP76 purified from the wild-type SCLC. However, this activity was significantly lower than that of RLIP76 purified from the wild-type NSCLC. After siRNA mediated depletion of PKCalpha, DOX-transport activities of RLIP76 purified from SCLC and NSCLC were indistinguishable. Depletion of PKCalpha inhibited the growth of NSCLC more than SCLC cells (70+/-3% vs. 43+/-5%, respectively). PKCalpha-depletion lowered the IC(50) of NSCLC cell lines for DOX to the same level as that observed for SCLC. RLIP76(-/-) mouse embryonic fibroblasts (MEFs) were significantly more sensitive to DOX as compared with RLIP76(+/+) MEFs (IC(50) 25 vs. 125nM, respectively). However, PKCalpha-depletion did not affect DOX-cytotoxicity towards RLIP76(-/-) MEFs, as opposed to RLIP76(+/+) MEFs which were sensitized by 2.2-fold. These results demonstrate that RLIP76 is a primary determinant of DOX-resistance, and that PKCalpha mediated accumulation defect and DOX-resistance in NSCLC is primarily due to differential phosphorylation of RLIP76 in SCLC and NSCLC.
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MESH Headings
- ATP-Binding Cassette Transporters/genetics
- ATP-Binding Cassette Transporters/metabolism
- Animals
- Antibiotics, Antineoplastic/pharmacology
- Antibiotics, Antineoplastic/therapeutic use
- Biological Transport, Active/drug effects
- Biological Transport, Active/genetics
- Carcinoma, Non-Small-Cell Lung/drug therapy
- Carcinoma, Non-Small-Cell Lung/genetics
- Carcinoma, Non-Small-Cell Lung/metabolism
- Carcinoma, Small Cell/drug therapy
- Carcinoma, Small Cell/genetics
- Carcinoma, Small Cell/metabolism
- Cell Line, Tumor
- Doxorubicin/pharmacology
- Doxorubicin/therapeutic use
- Drug Resistance, Neoplasm/drug effects
- Drug Resistance, Neoplasm/genetics
- Embryo, Mammalian/cytology
- Embryo, Mammalian/metabolism
- Enzyme Activation/drug effects
- Enzyme Activation/genetics
- Fibroblasts/cytology
- Fibroblasts/metabolism
- GTPase-Activating Proteins/genetics
- GTPase-Activating Proteins/metabolism
- Humans
- Lung Neoplasms/drug therapy
- Lung Neoplasms/genetics
- Lung Neoplasms/metabolism
- Mice
- Mice, Knockout
- Phosphorylation/drug effects
- Protein Kinase C-alpha/metabolism
- Protein Processing, Post-Translational/drug effects
- Protein Processing, Post-Translational/genetics
- RNA, Small Interfering/genetics
- RNA, Small Interfering/pharmacology
- Sequence Deletion/genetics
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Affiliation(s)
- Sharad S Singhal
- Department of Chemistry and Biochemistry, University of Texas at Arlington, 401 W, 3rd Street, CPB RM # 312, Arlington, TX 76019-0065, USA
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4
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Okajo A, Matsumoto KI, Mitchell JB, Krishna MC, Endo K. Competition of nitroxyl contrast agents as an in vivo tissue redox probe: Comparison of pharmacokinetics by the bile flow monitoring (BFM) and blood circulating monitoring (BCM) methods using X-band EPR and simulation of decay profiles. Magn Reson Med 2006; 56:422-31. [PMID: 16810697 DOI: 10.1002/mrm.20958] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Nitroxyl radicals used as tissue redox-sensitive contrast agents in electron paramagnetic resonance (EPR) and/or NMR imaging should satisfy the following two conditions: 1) the molecules disperse into tissues rapidly, and 2) paramagnetic loss occurs by simple reduction of the radical. The pharmacokinetic trends of several nitroxyl contrast agents were compared with the results obtained by bile flow monitoring (BFM) and blood circulation monitoring (BCM) methods using X-band EPR. The nitroxyl radicals (TEMPO, TEMPONE (oxo-TEMPO), and amino-TEMPO) showed additional EPR signals in the bile that were attributed to metabolites formed during transport from blood to bile through the liver. However, the highly hydrophilic CAT-1 (trimethylammonium-TEMPO), which has low membrane permeability, showed minimal concentration in the bile. Probes that have carboxyl moiety, such as carboxy-TEMPO and carboxy-PROXYL, can be transported via anion transporter into hepatic cells. The EPR signal decay profiles of the nitroxyl radicals were simulated based on the experimental data. The simulation, which we previously applied to mouse blood, was modified to simultaneously fit the experimental results of BFM and BCM obtained with rats. The simulation data showed the simplicity/complexity of the pharmacokinetic mechanisms and that carbamoyl-PROXYL and TEMPOL (hydroxy-TEMPO) are suitable contrast agents for assessing tissue redox status.
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Affiliation(s)
- Aya Okajo
- Department of Physical Chemistry, Showa Pharmaceutical University, Machida, Tokyo, Japan
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5
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Singhal SS, Yadav S, Singhal J, Drake K, Awasthi YC, Awasthi S. The role of PKCα and RLIP76 in transport-mediated doxorubicin-resistance in lung cancer. FEBS Lett 2005; 579:4635-41. [PMID: 16087181 DOI: 10.1016/j.febslet.2005.07.032] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2005] [Revised: 07/11/2005] [Accepted: 07/19/2005] [Indexed: 10/25/2022]
Abstract
In deletion mutant analyses of potential phosphorylation sites in RLIP76, we identified T297 and S509 as targets for phosphorylation by PKCalpha. Phosphorylation at T297 increased doxorubicin (DOX)-transport activity approximately 2-fold for RLIP76 purified from recombinant source, or from three small (H69, H1417, H1618) and three non-small cell, one each derived from H226 (squamous), H358 (bronchio alveolar), and H1395 (adenocarcinoma) lung cancer cell lines. T297 phosphorylation conferred sensitivity to tryptic digestion at R293. The specific activity for DOX-transport by RLIP76 purified from non-small cell, which was primarily in the phosphorylated form, was approximately twice that in small cell lung cancer cell lines. These finding offer a novel explanation for the observed intrinsic differences in sensitivity to DOX between non-small cell and small cell lung cancer cell lines.
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Affiliation(s)
- Sharad S Singhal
- Department of Chemistry and Biochemistry, 502 Yates St., Science Hall #223, University of Texas at Arlington, Arlington, TX 76019-0065, USA.
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6
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Awasthi S, Singhal SS, Sharma R, Zimniak P, Awasthi YC. Transport of glutathione conjugates and chemotherapeutic drugs by RLIP76 (RALBP1): a novel link between G-protein and tyrosine kinase signaling and drug resistance. Int J Cancer 2003; 106:635-46. [PMID: 12866021 DOI: 10.1002/ijc.11260] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Our studies have shown that RLIP76 (RALBP1), a 76 kDa Ral-binding, Rho/Rac-GAP and Ral effector protein, is a novel multispecific transporter of xenobiotics as well as GS-Es. Like previously characterized ABC transporters, it mediates ATP-dependent transport of structurally unrelated amphiphilic xenobiotics and displays inherent ATPase activity, which is stimulated by its substrate allocrites. It does not have significant sequence homology with ABC transporters and differs from the ABC transporters in several other important aspects, including (i) lack of any close homologs in humans, (ii) lack of a classical Walker domain, (iii) integral membrane association without clearly defined transmembrane domains and (iv) its role as a direct link to Ras/Ral/Rho and EGF-R signaling through its multifunctional nature, including GAP activity, regulation of exocytosis as well as clathrin-coated pit-mediated receptor endocytosis. Its multifunctional nature derives from the presence of multiple motifs, including a Rho/Rac GAP domain, a Ral effector domain binding motif, 2 distinct ATP-binding domains, a H(+)-ATPase domain, PKC and tyrosine kinase phosphorylation sites and the ability to undergo fragmentation into multiple smaller peptides which participate as components of macromolecular functional complexes. One of the physiologic functions of RLIP76 is regulation of intracellular concentration of the electrophilic intermediates of oxidative lipid metabolism by mediating efflux of GS-E formed from oxidative degradation of arachidonic acid, including leukotrienes and the 4HNE-GSH conjugate. RLIP76-mediated transport of amphiphilic chemotherapeutic agents such as anthracyclines and vinca alkaloids as well as GS-E produced during oxidative metabolism places this multifunctional protein in a central role as a resistance mechanism for preventing apoptosis caused by chemotherapeutic agents and a variety of external/internal stressors, including oxidative stress, heat shock and radiation.
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Affiliation(s)
- Sanjay Awasthi
- Department of Chemistry and Biochemistry, University of Texas at Arlington, Arlington, TX 76019, USA.
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7
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Awasthi S, Sharma R, Singhal SS, Zimniak P, Awasthi YC. RLIP76, a novel transporter catalyzing ATP-dependent efflux of xenobiotics. Drug Metab Dispos 2002; 30:1300-10. [PMID: 12433796 DOI: 10.1124/dmd.30.12.1300] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Transport of xenobiotics and their metabolites by ATP-binding cassette (ABC) transporters particularly P-glycoprotein (Pgp) and the multidrug resistance associated protein (MRP1) has been extensively studied during last decade. Our recent studies demonstrate that RLIP76, a previously known GTPase-activating protein catalyzes ATP-dependent, uphill transport of anionic glutathione conjugates as well as of weakly cationic anthracyclines including doxorubicin (Adriamycin), a widely used drug in cancer chemotherapy. RLIP76 has inherent ATPase activity, which is stimulated by doxorubicin and glutathione conjugates. RLIP76 does not meet the criteria for classical ABC proteins such as MRP1 or Pgp, but similar to ABC proteins, it has two ATP-binding sequences, (69)GKKKGK(74) and (418)GGIKDLSK(425). Mutations in these sequences abrogate its ATP-binding, ATPase activity, and transport function. Purified RLIP76 when reconstituted in proteoliposomes mediates ATP-dependent saturable transport of doxorubicin and glutathione conjugates. Transfection of K562 cells with RLIP76 confers these cells resistance to doxorubicin and 4-hydroxynonenal. Cells enriched with RLIP76 also acquire resistance to radiation toxicity. RLIP76 also catalyzes the transport of physiologic ligands such as leukotrienes (LTC4) and the conjugate of 4-hydroxynonenal and glutathione. In some cells (e.g., erythrocytes and lung cancer cells), the majority of transport activity for Adriamycin and glutathione conjugates including LTC4 is accounted for by RLIP76. These studies strongly suggest that RLIP76-mediated transport of organic ions has physiological and toxicological relevance and that it may play an important role in the mechanism of drug resistance.
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Affiliation(s)
- Sanjay Awasthi
- Department of Chemistry and Biochemistry, University of Texas at Arlington, Arlington, Texas
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8
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Hishikawa S, Kobayashi E, Sugimoto K, Miyata M, Fujimura A. Diurnal variation in the biliary excretion of flomoxef in patients with percutaneous transhepatic biliary drainage. Br J Clin Pharmacol 2001; 52:65-8. [PMID: 11453891 PMCID: PMC2014506 DOI: 10.1046/j.0306-5251.2001.01418.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/1999] [Accepted: 03/16/2001] [Indexed: 11/20/2022] Open
Abstract
AIMS To examine diurnal variation in biliary excretion of flomoxef. METHODS Flomoxef (1 g) was injected intravenously in eight patients with percutaneous transhepatic cholangiography with drainage at 09.00 h and 21.00 h by a cross-over design with a 36 h washout period. Drained biliary fluid was collected for 6 h after each dosing. These patients still had mild to moderate hepatic dysfunction. RESULTS Bile flow and bile acid excretion for 6 h after dosing did not differ significantly between the 09.00 h and 21.00 h treatments. The maximum concentration of biliary flomoxef was significantly greater and its total excretion for 6 h tended to be greater after the 21.00 h dose [maximum concentration (microg ml(-1)): 34.2 +/- 29.9 (09.00 h dose) vs 43.5 +/- 28.3 (21.00 h dose) (95% confidence interval for difference: 2.6 approximately 15.9, P = 0.013); total excretion (mg 6 h(-1)): 1.4 +/- 1.3 (09.00 h dose) vs 1.6 +/- 1.2 (21.00 h dose) (95% confidence interval for difference: -26.8, 313.7, P = 0.087)]. The period that biliary flomoxef remained above the minimal inhibitory concentration did not differ significantly between the two treatment times. CONCLUSIONS These results suggest that biliary excretion of flomoxef shows diurnal variation. However, as the difference was relatively small, flomoxef could be given at any time of day without any dosage adjustments.
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Affiliation(s)
- S Hishikawa
- Department of Clinical Pharmacology, Jichi Medical School, Tochigi, Japan
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9
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Zimniak P, Pikula S, Bandorowicz-Pikula J, Awasthi YC. Mechanisms for xenobiotic transport in biological membranes. Toxicol Lett 1999; 106:107-18. [PMID: 10403654 DOI: 10.1016/s0378-4274(99)00061-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Affiliation(s)
- P Zimniak
- Department of Internal Medicine, University of Arkansas for Medical Sciences, and McClellan VA Hospital Medical Research, Little Rock, USA
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10
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Koopen NR, Müller M, Vonk RJ, Zimniak P, Kuipers F. Molecular mechanisms of cholestasis: causes and consequences of impaired bile formation. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1408:1-17. [PMID: 9784591 DOI: 10.1016/s0925-4439(98)00053-2] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- N R Koopen
- Groningen Institute for Drug Studies, Center for Liver, Digestive and Metabolic Diseases, CMC IV, Room Y2115, University Hospital Groningen, P.O. Box 30.001, 9700 RB Groningen, The Netherlands
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11
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Knowles AF, Penefsky HS. Reconstitution of beef heart mitochondrial F0F1 in reverse phase evaporation vesicles. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1329:311-20. [PMID: 9371423 DOI: 10.1016/s0005-2736(97)00123-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Beef heart mitochondrial F0F1 was reconstituted in proteoliposomes by a new procedure. MF0F1 was inserted in preformed reverse phase evaporation vesicles of large diameters prepared from asolectin (MF0F1-REV). Reconstitution was mediated by Triton X-100, which was subsequently removed by treatment with Bio-Beads. Parameters which resulted in optimal reconstitution were described. The MF0F1-REV proteoliposomes catalyzed an exchange between Pi and ATP and were capable of proton pumping. Both reactions were inhibited by oligomycin and uncoupler of oxidative phosphorylation. The range of Pi-ATP exchange activity of the proteoliposomes (70-110 nmol min[-1] mg[-1]) compared favorably with activities obtained in vesicles reconstituted by cholate dialysis or cholate dilution. The most important aspect of this method is that, unlike other reconstitution methods, exogenous F1 and other coupling factors are not required to obtain high Pi-ATP exchange activity by MF0F1-REV. This simple and rapid reconstitution procedure should be useful for future studies dealing with functional analysis of MF0F1.
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Affiliation(s)
- A F Knowles
- Department of Biochemistry and Molecular Biology, SUNY Health Science Center, Syracuse, NY 13210, USA.
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12
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Barth A, Fleck C, Klinger W. Development of organic anion transport in the liver. EXPERIMENTAL AND TOXICOLOGIC PATHOLOGY : OFFICIAL JOURNAL OF THE GESELLSCHAFT FUR TOXIKOLOGISCHE PATHOLOGIE 1996; 48:421-32. [PMID: 8765687 DOI: 10.1016/s0940-2993(96)80052-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- A Barth
- Institute of Pharmacology and Toxicology, Friedrich Schiller University Jena, Germany
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13
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Kreisel W, Spamer C, Heilmann C. Partial characterization of a new nucleotide binding glycoprotein of hepatocyte plasma membrane. Biochem Pharmacol 1996; 51:1269-76. [PMID: 8787541 DOI: 10.1016/0006-2952(95)02439-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Hepatocyte plasma membranes contain a glycosylated 230-kDa Ca(2+) -dependent, Mg(2+)-stimulated ATPase (pgp230), which consists of two subunits, one of 120 kDa and the other of 110 kDa. pgp230 can be enriched by the use of affinity chromatography on Concanavalin A-Sepharose, wheat germ lectin-Sepharose, and 5'-AMP-Sepharose. It has a high-affinity Ca2+ binding site. In the presence of Ca2+, it forms a phosphorylated intermediate by autocatalytic transfer of the terminal phosphate residue from ATP. Maximal Ca(2+)-dependent autophosphorylation is observed at pH 5-6. Photoaffinity labeling using 8-azido-[alpha-32P]ATP or [y-32P]ATP confirms the presence of ATP binding sites. Incubation with [alpha-32P]ATP leads to a rapid but transient labeling of pgp230. Various nucleotides, nucleotide receptor agonists, or antagonists inhibit Ca(2+)-dependent phosphorylation by [y-32P]ATP. The concentrations of half-maximal inhibition range from 10(-7) M to 10(-3) M. The rank order of inhibitory potency is: ATP > alpha,beta-methylene-ATP > CTP = TTP > y-4-amino-phenyl-ATP = 2-methyl-thio-ATP > UTP = GTP > GDP = ADP = beta,y-methylene-ATP = beta, y-methylene-TTP = beta,y-methylene-GTP = adenosine-5'-O-2-thiodiphosphate = CMP = AMP > adenosine > cytidine > guanosine = suramin > Reactive blue 2 > iso-butyl-methyl-xanthine > thymidine > uridine. These data suggest a nucleotide binding capacity of this new hepatocyte membrane glycoprotein. Further investigations should be carried out to reveal its biological function.
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Affiliation(s)
- W Kreisel
- Klinikum Der Albert-Ludwigs-Universität, Medizinische Klinik, Abteilung Gastroenterologie, Hepatologie und Endokrinologie, Freiburg, Germany
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Matsuda Y, Epstein LF, Gatmaitan Z, Arias IM. The role of thiols in ATP-dependent transport of S-(2,4-dinitrophenyl)glutathione by rat liver plasma membrane vesicles. BIOCHIMICA ET BIOPHYSICA ACTA 1996; 1279:35-42. [PMID: 8624358 DOI: 10.1016/0005-2736(95)00241-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The effect of thiol/disulfide exchange on ATP-dependent S-(2,4-dinitrophenyl)glutathione (GS-DNP) transport was studied in sodium nitrate treated rat liver plasma membrane vesicles. Transport followed Michaelis-Menten kinetics with an apparent Km of 9.6 microM for GS-DNP and 124 microM for ATP. 5,5'-Dithiobis(2-nitrobenzoate) (DTNB) and N-ethylmaleimide (NEM) efficiently inactivated GS-DNP transport activity in a dose- and time-dependent manner. Half-maximal inactivation occurred in 10 min at 40 microM for DTNB and 550 microM for NEM. Inactivation by DTNB was reversed by dithiothreitol. S-(N-Ethyl)maleimyl glutathione and/or ATP-Mg2+, but neither S-(N-ethyl)maleimyl cysteinylglycine nor oxidized glutathione could protect transport activity from inactivation by NEM or cystamine. These results suggest that reactive thiols are located near the active site of the transporter and that S-alkyl and the gamma-glutamyl residues of glutathione are important for protection. Biological disulfides which were tested included cystine, oxidized glutathione, oxidized Coenzyme-A, oxidized lipoic acid, and oxidized lipoamide; cystamine was the most potent reversible inactivator. Molecular oxygen also inactivated transport activity, which was recovered on addition of dithiothreitol, suggesting intramolecular disulfide formation by vicinal thiols. We interpret these results to indicate that the ATP-dependent GS-DNP transporter contains two or more thiols which are necessary for the maintenance of transport activity. The reversible inactivation of the activity by biological disulfides suggests that the transporter may be regulated by thiol/disulfide exchange in vivo.
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Affiliation(s)
- Y Matsuda
- Department of Physiology, Tufts University School of Medicine, Boston, MA 02111, USA
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Oude Elferink RP, Meijer DK, Kuipers F, Jansen PL, Groen AK, Groothuis GM. Hepatobiliary secretion of organic compounds; molecular mechanisms of membrane transport. BIOCHIMICA ET BIOPHYSICA ACTA 1995; 1241:215-68. [PMID: 7640297 DOI: 10.1016/0304-4157(95)00006-d] [Citation(s) in RCA: 249] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- R P Oude Elferink
- Department of Gastrointestinal and Liver Diseases, Academic Medical Center, AZ Amsterdam, The Netherlands
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16
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Pikula S, Hayden JB, Awasthi S, Awasthi YC, Zimniak P. Organic anion-transporting ATPase of rat liver. I. Purification, photoaffinity labeling, and regulation by phosphorylation. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(18)47022-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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