Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.5.1.18 (glutathione S-transferase)
 22,582 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mechanism of activation of microsomal glutathione transferase in isolated liver cells by diisapropylidene acetone (phorone) was investigated. Phorone (1 mM) causes a time-dependent increase (up to 2.6-fold) in the glutathione transferase activity of microsomes isolated from treated hepatocytes. Since phorone reacts with sulfhydryl groups, the possibility that this compound activated microsomal glutathione transferase directly was studied. It was found that neither the activity of the purified enzyme nor that in isolated microsomes is affected by phorone. It has been suggested [Masukawa T and Iwata H, Biochem Pharmacol 35: 435-438, 1986] that activation of microsomal glutathione transferase by phorone in vivo is mediated through thiol-disulfide interchange involving oxidized glutathione (GSSG). It is shown here that the glutathione transferase activity of isolated microsomes, which was increased by the addition of 10 mM GSSG, can be decreased to the basal level with 0.1 M dithioerythritol. Dithioerythritol, on the other hand, only marginally decreases the glutathione transferase activity in microsomes isolated from phorone-treated hepatocytes. This finding argues against a role for thiol-disulfide interchange in the activation of the enzyme by phorone. Furthermore, the glutathione depletion caused by phorone does not seem to be responsible for activation per se, since other thiol depletors [e.g. diethylmaleate (DEM)] do not affect the activity of the enzyme. Immunoblot analysis of microsomes isolated from phorone-treated hepatocytes did not reveal any partial proteolysis which might have accounted for the activation. It is suggested that activation of microsomal glutathione transferase by phorone proceeds through a mechanism which might reflect an in vivo regulation of this enzyme. Additional compounds which have been shown to activate the microsomal glutathione transferase in vivo were also tested and significant activation was obtained with 1,2-dibromoethane (1.4-fold) but not with DEM or carbon tetrachloride. Activation was also obtained with 1-chloro-2,4-dinitrobenzene (CDNB) (1.6-fold) and to a small extent with t-butyl hydroperoxide (1.2-fold). The activation by 1,2-dibromoethane and CDNB is probably mediated through covalent binding, considering the known alkylating properties of these compounds. CDNB is the first substrate shown to activate the microsomal glutathione transferase implying that electrophilic compounds which are substrates can increase the rate of their own elimination by reacting with this enzyme. In addition, activation by t-butyl hydroperoxide indicates that oxidative stress can activate microsomal glutathione transferase.
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PMID:Studies on the activation of rat liver microsomal glutathione transferase in isolated hepatocytes. 173

The liver is the only tissue that has been demonstrated directly to secrete glutathione into the plasma. The present experiments were carried out to determine whether extrahepatic tissues secrete the reduced form of glutathione (GSH) as well. Phorone, a compound that depletes glutathione through glutathione S-transferase-dependent conjugation with GSH, was administered to fasted rats in a dose of 250 mg/kg. Two hours later, glutathione concentrations were reduced to the following: liver, 2%; plasma, 17%; and skeletal muscle, 63%. This showed that plasma and muscle glutathione were not depleted to the same extent as liver glutathione. Glutathione concentration in plasma from the hepatic vein was not higher than concentrations in plasma from the portal vein and from the aorta, indicating that the depleted liver was not releasing glutathione into the plasma. Total glutathione and GSH were higher in plasma from the femoral vein than in plasma from the aorta under these same conditions. This indicates that the leg releases GSH under conditions of absent hepatic GSH release when plasma glutathione concentrations are decreased. These results suggest that muscle secretes GSH into the extracellular space and raise the possibility that other tissues secrete GSH as well. Further studies will be required to determine whether GSH release by extrahepatic tissues is affected by the plasma glutathione concentration.
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PMID:Reduced glutathione release into rat plasma by extrahepatic tissues. 757 50

Metabolism of methylene chloride, or dichloromethane (DCM), plays a key role in determining the kinetics and carcinogenicity of the halocarbon. The objectives of this study were: to evaluate and optimize the vial equilibration technique, originally described by Sato and Nakajima (1979a), in order to characterize the hepatic metabolism of DCM by Sprague-Dawley rats; to employ different hepatic microsomal preparations to examine buffer effects on DCM metabolism; and to assess the relative importance and metabolic constants of the mixed-function oxidase (MFO) and glutathione (GSH) S-transferase (GST) metabolic pathways. A crude liver homogenate (20% W/V) was prepared from perfused livers of male Sprague-Dawley (S-D) rats (275-325 g). A 30% glycerol buffer was found to significantly inhibit DCM metabolism, while 0.25 M sucrose buffer containing 10 mM EDTA and 1.15% KCl did not. DCM was incubated with the liver 10,000 g supernatant or microsomes and cofactors in sealed headspace vials. Disappearance of DCM, as a measure of the chemical's metabolism, was monitored by headspace gas chromatography. Different trials were conducted to elucidate time-, enzyme-, and substrate-activity relationships. The scaled-up K(m) and Vmax values for the microsomal fraction were quite similar to optimized in vivo values reported by other investigators. In the current study, DCM appeared to be metabolized preferentially by cytochrome P450 IIE1, since substrates (e.g., pyrazole, ethanol, and glycerol) for this isozyme completely inhibited DCM metabolism. Thus, glycerol should not be used as a P450 stabilizer for preparation or storage of microsomes. Phorone pretreatment caused marked hepatic GSH depletion, but had little effect on the overall rate of DCM metabolism. Quantitatively, the GST pathway in the cytosol played a very minor role in DCM metabolism. It was not possible to accurately calculate metabolic constants for this pathway in S-D rats. The vial equilibration technique, as described here, is a relatively simple and reliable method, which should be broadly applicable for measuring the microsomal metabolism of DCM and other VOCs.
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PMID:Use of the vial equilibration technique for determination of metabolic rate constants for dichloromethane. 880 40