Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A method was developed to measure the formation of glutathione adducts of 1-chloro-2,4-dinitrobenzene (CDNB) and 2,4-dichloro-1-nitrobenzene (DCNB) in periportal and pericentral regions of the liver lobule in the isolated perfused rat liver by surface reflectance spectrophotometry. Conjugates of DCNB and CDNB are released from livers of normal and phenobarbital-treated rats during perfusion in either the anterograde or the retrograde direction at maximal rates around 13-15 mumol/g/hr. The formation of S-(1-chloro-4-nitrophenyl)-glutathione and S-(2,4-dinitrophenyl)-glutathione by the liver decreased the amount of 366-nm light reflected from the liver surface detected with a large-tipped (2 mm) fiberoptic light guide. Initial rates of decrease in reflected light correlated highly with maximal rates of conjugate formation by the liver. Subsequently, micro-light guides were placed on periportal and pericentral regions of the liver lobule. Rates of glutathione adduct formation were calculated from the proportion of the total change in rate of reflected 366-nm light which occurred in each region and the overall rate of product formation by the liver. Changes in the reflectance signal require reduced glutathione (GSH) and were shown to originate from intracellular conjugate formation and not from adducts in the bile canaliculus. Livers from normal rats produced conjugated products from DCNB (100 microM) at maximal rates of 14 and 15 mumol/g/hr in periportal and pericentral regions of the liver lobule, respectively. With CDNB as substrate, changes in reflected light at 366 nm were detected nearly exclusively in periportal regions of the lobule in livers from normal rats. In sharp contrast, CDNB and DCNB were conjugated exclusively in periportal regions of the lobule at rates of 21-22 mumol/g/hr in livers from phenobarbital-treated rats (i.e., the reflectance signal was not altered by these substrates in pericentral areas). When CDNB and DCNB were infused into livers from phenobarbital-treated rats perfused in the retrograde direction, decreases in reflected light at 366 nm were detected initially in pericentral areas followed in about 12 min by changes in periportal regions. Maximal rates of adduct formation in both regions reached 25 mumol/g/hr during perfusion in the retrograde direction. Thus, pericentral regions indeed possess the capacity to conjugate both CDNB and DCNB. When glutathione synthesis was inhibited with L-buthionine sulfoximine treatment (6 mmol/kg), which partially depletes GSH, CDNB was conjugated in both periportal and pericentral regions of the liver lobule in livers from phenobarbital-treated rats.(ABSTRACT TRUNCATED AT 400 WORDS)
Mol Pharmacol 1986 Jan
PMID:A new method to study glutathione adduct formation in periportal and pericentral regions of the liver lobule by micro-reflectance spectrophotometry. 394 30

Horseradish peroxidase catalyzed the polymerization of acetaminophen. Addition of reduced glutathione (GSH) to reaction mixtures resulted in decreased polymerization and formation of minor amounts of GSH-acetaminophen conjugates. The conjugates were identified as 3-(glutathion-S-yl)acetaminophen and 3-(glutathion-S-yl)diacetaminophen. Horseradish peroxidase also catalyzed polymerization of synthetic 3-(glutathion-S-yl)acetaminophen to a dimer conjugate. In contrast to acetaminophen, 3-(glutathion-S-yl)acetaminophen oxidation was slowly catalyzed by horseradish peroxidase. However, in reaction mixtures containing equimolar concentrations of acetaminophen and synthetic 3-(glutathion-S-yl)acetaminophen, the formation of 3-(glutathion-S-yl)diacetaminophen and 3-(diglutathion-S-yl)diacetaminophen was rapid and accounted for approximately 95% of the products, whereas acetaminophen polymers accounted for only 5% of the products. These findings suggest that horseradish peroxidase catalyzed the one-electron oxidation of acetaminophen to N-acetyl-p-benzosemiquinone imine which preferentially polymerized rather than reacted with GSH. N-Acetyl-p-benzosemiquinone imine may also oxidize 3-(glutathion-S-yl)acetaminophen to form acetaminophen and 3-(glutathion-S-yl)-N-acetyl-p-benzosemiquinone imine. The data indicate that once this conjugate radical is formed it reacts with either N-acetyl-p-benzosemiquinone minine or 3-(glutathion-S-yl)-N-acetyl-p-benzosemiquinone imine via a radical termination mechanism.
Mol Pharmacol 1986 Feb
PMID:Horseradish peroxidase-catalyzed oxidation of acetaminophen to intermediates that form polymers or conjugate with glutathione. 395 29

OFF products of horseradish peroxidase (EC 1.11.1.7)-catalyzed oxidation of p-phenetidine were isolated and reactive species were trapped with reduced glutathione (GSH) and butylated hydroxyanisole (BHA). When BHA was added to a reaction mixture after 5 min, subsequent TLC and mass spectrometric analysis revealed the formation of an adduct of BHA and 4-(ethoxyphenyl)-p-benzoquinone diimine (A). The diimine derivative (A) was unstable and its expected degradation products, 4-(ethoxyphenyl)-p-benzoquinone imine (B) and ammonia, were recovered from the reaction in stoichiometric amounts. Ethanol was an early product of the reaction presumably resulting from radical coupling reactions and its formation agreed with the combined production of A and B, suggesting that this was its sole route of formation. The addition of GSH to a reaction at various times and subsequent TLC and high performance liquid chromatographic analysis revealed the presence of at least seven conjugates. Two conjugates were identified by fast atom bombardment mass spectrometry, one as a mono-GSH conjugate of A and another as a mono-GSH conjugate of B. When purified [14C]B was mixed with [3H]GSH, three conjugates were isolated by high performance liquid chromatography, two of which were tentatively identified as di-GSH conjugates. The conjugates isolated existed in both oxidized and reduced forms which could be easily interconverted by redox processes. The production of such reactive species and their conjugates in vivo may be a useful indicator of peroxidase-catalyzed metabolism.
Mol Pharmacol 1985 Feb
PMID:Characterization and mechanism of formation of reactive products formed during peroxidase-catalyzed oxidation of p-phenetidine. Trapping of reactive species by reduced glutathione and butylated hydroxyanisole. 396 71

Lethal cell injury from hepatotoxic drugs has been postulated to result from an alteration in cell Ca2+ homeostasis. ATP-dependent Ca2+ uptake by the plasma membrane has a sulfhydryl-dependent functional moiety and, therefore, could be vulnerable to chemically reactive drug intermediates. Thus, alkylating hepatotoxins given in vivo were examined for their ability to inhibit Ca2+ accumulation by plasma membrane vesicles isolated from livers of adult male rats. ATP-dependent Ca2+ accumulation was decreased 62% by bromobenzene, 76% by acetaminophen, and 92% by CCl4. Mitochondrial Ca2+ uptake was minimally affected by the toxins, and only CCl4 affected Ca2+ accumulation by liver microsomes. The effect of acetaminophen on plasma membrane Ca2+ uptake was apparent as early as 45 min postdose. Depletion of protective intracellular GSH by diethyl maleate treatment (400 mg/kg) alone minimally decreased control plasma membrane uptake activity, although the GSH depletion markedly potentiated the effect of acetaminophen on the plasma membrane and on necrosis. Alkylation of sites on the plasma membrane may be a key chemical-macromolecule interaction in drug-induced liver necrosis, and inhibition of plasma membrane Ca2+ regulation may provide a connecting link between the alkylation hypothesis and the perturbed Ca2+ homeostasis hypothesis of lethal cell injury.
Mol Pharmacol 1985 Jul
PMID:ATP-dependent calcium uptake by rat liver plasma membrane vesicles. Effect of alkylating hepatotoxins in vivo. 402 97

N-Acetyl-p-benzoquinone imine (NAPQI), a reactive metabolite of acetaminophen, rapidly reacts at physiological pH with glutathione (GSH) forming an acetaminophen-glutathione conjugate and stoichiometric amounts of acetaminophen and glutathione disulfide (GSSG). The same reaction products are formed in isolated hepatocytes incubated with NAPQI. In hepatocytes which have been treated with 1,3-bis-(2-chloroethyl)-1-nitrosourea (BCNU) in order to inhibit glutathione reductase, the initial rise in GSSG concentration in the presence of NAPQI is maintained, whereas GSSG is rapidly reduced back to GSH in untreated hepatocytes. Oxidation by NAPQI of GSH to GSSG and the reduction of GSSG back to GSH by the NADPH-dependent glutathione reductase appear to be responsible for the rapid oxidation of NADPH that occurs in hepatocytes incubated with NAPQI in that the effect is blocked by pretreatment of cells with BCNU. When added to hepatocytes, NAPQI not only reacts with GSH but also causes a loss in protein thiol groups. The loss in protein thiols occurs more rapidly in cells pretreated with BCNU or diethylmaleate. Whereas both of these treatments enhance cytotoxicity caused by NAPQI, BCNU pretreatment has no effect on the covalent binding of [14C-ring]NAPQI to cellular proteins. Furthermore, dithiothreitol added to isolated hepatocytes after maximal covalent binding of [14C-ring]NAPQI but preceding cell death protects cells from cytotoxicity and regenerates protein thiols. Thus, the toxicity of NAPQI to isolated hepatocytes may result primarily from its oxidative effects on cellular proteins.
Mol Pharmacol 1985 Sep
PMID:Mechanisms of N-acetyl-p-benzoquinone imine cytotoxicity. 403 31

The possibility that myocardial ischaemia alters the defence mechanisms against oxygen toxicity has been investigated. Ischaemia was induced in isolated, perfused rabbit hearts by reducing coronary flow from 25 ml/min to 1 ml/min for 90 min. Two different degrees of ischaemic damage have been achieved using either spontaneously beating or electrically stimulated hearts. The effects of post-ischaemic reperfusion were also followed for 30 min. Tissue activity of superoxide dismutase (SOD), glutathione peroxidase and reductase (GPD and GRD) have been determined together with tissue content of reduced and oxidized glutathione (GSH and GSSG) and of protein SH groups. The changes in myocardial ATP and CP content and release of CPK and of GSH and GSSG were also determined. Systolic and diastolic pressures were continuously monitored. In the spontaneously beating hearts ischaemia induced a reduction of tissue GSH and protein SH groups. On reperfusion there was a recovery of mechanical function, a transient release of GSH into the coronary effluent and an increase of tissue GSH. In the paced hearts, ischaemia resulted in 50% reduction of mitochondrial SOD activity together with a reduction of tissue GSH and protein SH groups. Reperfusion induced a massive release of CPK and of GSH and GSSG, a further reduction of tissue GSH concomitant with an increase of GSSG and no recovery of mechanical function. GPD and GRD activity were not affected by ischaemia and reperfusion. These data indicate that severe ischaemia induces a reduction of the protective mechanisms against oxygen toxicity.
J Mol Cell Cardiol 1985 Oct
PMID:Oxygen-mediated myocardial damage during ischaemia and reperfusion: role of the cellular defences against oxygen toxicity. 406 39

N-Acetyl-3,5-dimethyl-p-benzoquinone imine, N-acetyl-2,6-dimethyl-p-benzoquinone imine, and N-acetyl-p-benzoquinone imine were synthesized via the oxidation of 3,5-dimethylacetaminophen, 2,6-dimethylacetaminophen, and acetaminophen, respectively. All three quinone imines were rapidly reduced to their corresponding semiquinone imines by NADPH-cytochrome P-450 reductase. All three benzoquinone imines underwent comproportionation with their respective phenols to yield the corresponding semiquinone imines, which in the presence of oxygen gave superoxide. Identification of this latter free radical was based on spin-trapping techniques. Reduced GSH was found to be an excellent nucleophile toward N-acetyl-2,6-dimethyl-p-benzoquinone imine, whereas this thiol behaved as a one-electron reductant toward N-acetyl-3,5-dimethyl-p-benzoquinone imine. Finally, GSH was determined to act as both a nucleophile and a reductant toward N-acetyl-p-benzoquinone imine.
Mol Pharmacol 1984 Jan
PMID:Reduction and glutathione conjugation reactions of N-acetyl-p-benzoquinone imine and two dimethylated analogues. 632 48

Thiourea, phenylthiourea, and methimazole perfused into rat liver stimulated the biliary efflux of GSSG without affecting the excretion of GSH into either the bile or the caval perfusate. The thiocarbamide moiety appears essential, since perfusion with urea, phenylurea, or N-methylimidazole did not stimulate GSSG release. Hydrogen peroxide is also not an obligatory intermediate, since thiocarbamide-induced GSSG efflux was undiminished in livers from selenium-deficient animals. The response was also not affected by N-benzylimidazole, a potent cytochrome P-450 inhibitor, which suggests that this monooxygenase is not involved. However, the results are consistent with a model based on S-oxygenation of thiocarbamides to formamadine sulfenates catalyzed exclusively by the flavin-containing monooxygenase. The resulting sulfenate is reduced by GSH, yielding GSSG and the parent thiocarbamide. Rapid cellular oxidation of GSH by this mechanism leads to biliary efflux of the disulfide.
Mol Pharmacol 1984 Jul
PMID:Increased biliary GSSG efflux from rat livers perfused with thiocarbamide substrates for the flavin-containing monooxygenase. 643 Dec 60

Uroporphyrinogen (urogen) decarboxylase catalyzes the decarboxylation of 8- to 4-carboxyl porphyrinogen during heme biosynthesis in mammalian tissues. The specific activity of renal urogen decarboxylase was shown to be approximately one-third that of the hepatic enzyme and to be readily inactivated by HgCl2 following acute treatment or at concentrations as low as 50 microM in vitro. HgCl2 differentially inhibited the decarboxylation of 8- to 7- and 7- to lesser-carboxylated porphyrinogens in the kidney, suggesting that at least a two-stage process is involved in the catalytic action of the renal enzyme. In contrast, neither lead nor iron compounds inhibited renal urogen decarboxylase in concentrations as high as 1 mM in the reaction mixture. GSH increased renal but not hepatic urogen decarboxylase activity by over 4-fold in vitro when measured as total porphyrinogen products produced, and preferentially accelerated the decarboxylation of 7- to 4-carboxyl porphyrinogen. GSH also protected the renal enzyme from HgCl2 inhibition. These findings suggest that renal urogen decarboxylase catalyzes porphyrin decarboxylation significantly less rapidly than the hepatic enzyme, is readily inactivated by mercuric chloride, and may be GSH-dependent with respect to achieving optimal catalytic activity. These observations may be useful in characterizing the contribution of the kidney to the clinical manifestations of the inherited porphyrias and environmentally induced disorders of porphyrin metabolism.
Mol Pharmacol 1984 Sep
PMID:Studies on porphyrin metabolism in the kidney. Effects of trace metals and glutathione on renal uroporphyrinogen decarboxylase. 648 78

The effects of thiols, such as glutathione (GSH), and the cytosolic glutathione S-transferases on the microsomal metabolism of the hydrazide iproniazid to hydrocarbon products were investigated. Thiol compounds stimulated propane production and depressed propylene production. Addition of preparations of cytosolic proteins to the microsomal reaction mixtures in the presence of GSH depressed production of propane by more than 80% and propylene by 50% compared to the GSH-mediated reaction. The purified glutathione S-transferases A and B were most potent in eliciting this effect; isozymes AA, C, and E had little or no effect on hydrocarbon production. Further, a mixture of these purified isozymes in the concentrations known to exist in cytosol affected hydrocarbon production in a manner similar to cytosol. Experiments performed with isolated hepatocytes and an inhibitor of these cytosolic enzymes further supported the involvement of these enzymes in altered hydrocarbon production. These isozymes were subsequently shown to catalyze the formation of a GSH conjugate, S-(2-propyl)glutathione. The decreases in hydrocarbon production by microsomes in the presence of the glutathione S-transferases and GSH were accompanied by production of slightly larger amounts of conjugate. These data indicate that the cytosolic glutathione S-transferases interact with an oxidative microsomal metabolite of iproniazid to enzymatically produce an S-(2-propyl)glutathione conjugate and thus prevent formation of a reactive species which would otherwise chemically decompose to yield hydrocarbons or to covalently bind to cellular macromolecules.
Mol Pharmacol 1984 Nov
PMID:Effect of cytosolic components on the metabolism of the hydrazide iproniazid. 649 12


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