SEARCH · Search PubMed

Results for “Transferases”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 991 records · Page 55Linked to original sources

PubMed1996

In vivo potentiation of 1,2-dibromoethane hepatotoxicity by ethanol through inactivation of glutathione-s-transferase.

In the rat, a single ethanol (EtOH) pretreatment (2.5 g/kg b.w., per os) was able to strongly enhance the cytotoxicity of 1,2-dibromoethane (DBE)(87 mg/kg b.w., per os). The principal metabolic routes of DBE involve both oxidative and conjugative transformations. Microsomal cytochrome P450 content and dimethyl nitrosamine demethylase activity were not changed, while a significant loss of cytosolic total GSH-transferase was observed in rats killed 6 h after EtOH pretreatment. Pretreatment with methylpyrazole, an inhibitor of alcohol-dehydrogenase prevented the effects provoked by ethanol. The major EtOH metabolite, acetaldehyde. seemed thus to play a fundamental role in the mechanism responsible for the potentiation of DBE toxicity mediated by EtOH. To further support this hypothesis, disulfiram (75 mg/kg b.w.), an inhibitor of aldehyde dehydrogenase, was given i.p. to rats. When DBE was administered to disulfiram- and EtOH-pretreated rats, a marked increase of liver cytolysis was shown and cytosolic GSH-transferase activity was further inhibited if compared to that induced by EtOH treatment alone. The results are consistent with the hypothesis that EtOH given to rats increases DBE liver toxicity because its major metabolite, acetaldehyde, reduces the DBE conjugates to GSH transferase, with consequent shift of DBE metabolism to the oxidative route and accumulation of reactive oxidative intermediates no longer effectively conjugated with GSH.

Alcohol Dehydrogenase↗

PubMed1990

Rapid automated analysis of glutathione reductase, peroxidase, and S-transferase activity: application to cisplatin-induced toxicity.

We describe a rapid kinetic method for the automated determination of the xenobiotic-metabolizing enzymes glutathione reductase, glutathione peroxidase and glutathione S-transferase, and its application to the study of cisplatin-induced toxicity. Liver, kidney and urine from control and cisplatin-treated rats were used as the source of enzymes. Advantages over conventional spectrophotometric methods include speed (25 assays in 4 min), small sample size, and improved precision. We show that glutathione S-transferase activity in liver is slightly reduced by cisplatin treatment, whereas all three enzymes are reduced in the kidney. Glutathione-S-transferase activity appeared in urine between the third and seventh days after cisplatin injection. Using these enzyme activities in cisplatin-treated rats, we suggest that the renal enzymes are more sensitive markers of toxicity than hepatic enzymes.

Animals↗

PubMed1985

Characterization of glutathione S-transferases of human cornea.

Two cationic (pIs 9.1 and 7.6) and one anionic (pI 4.4) forms of glutathione S-transferase have been purified to an apparent homogeneity from human cornea using glutathione-linked affinity chromatography and isoelectric focusing. The substrate specificities of the three enzyme forms are significantly different from each other. None of the three forms of human cornea glutathione S-transferase express glutathione peroxidase II activity. Immunological and structural studies reveal that human cornea enzymes have structural similarities with glutathione S-transferases of other human tissues.

Chemical Phenomena↗

PubMed1982

5 alpha,6 alpha-Epoxy-cholestan-3 beta-ol (cholesterol alpha-oxide): A specific substrate for rat liver glutathione transferase B.

A semi-micro assay was developed for the conjugation of 5 alpha,6 alpha-epoxy-cholestan-3 beta-ol (cholesterol alpha-oxide) with glutathione. The soluble supernatant of rat liver homogenate catalysed the reaction at a rate of 0.2-0.5 pmol . min-1 . mg protein-1 with 4 microM cholesterol alpha-oxide, while the reaction in the presence of GSH alone was barely detectable. Enzymic activity in the soluble supernatant was due equally to the two forms of glutathione transferase B (approximately 100 pmol . min-1 . mg protein-1), glutathione transferases AA, A, C and E being unreactive. The activity of purified glutathione transferase B was about 5-times that expected from the activity of the soluble supernatant. Complex enzyme kinetics were obtained suggestive of substrate inhibition.

Animals↗

PubMed1984

The isozyme pattern of glutathione S-transferases in rat heart.

The isozyme pattern of glutathione S-transferases of rat heart differs markedly from that of liver. Heart lacks the majority of basic isozymes recognized in rat liver, and isoelectric focusing of glutathione S-transferases obtained from affinity chromatography on S-hexylglutathione-linked Sepharose 6B revealed that 3 major acidic isozymes with pI values of 6.8, 6.3 and 4.9 are present in heart, at least two of which were not found in liver. In addition, multiple bands were found in the pI range 5.0-5.5 for glutathione S-transferase activity and protein staining.

Animals↗

PubMed1991

Cysteine residues are not essential for the catalytic activity of human class Mu glutathione transferase M1a-1a.

To investigate the possible involvement of a Cys thiol in the catalysis of the human glutathione transferase M1a-1a, we constructed mutants of this enzyme wherein the four Cys residues present in the native enzyme were replaced by Ala residues. Three mutants, one where all four Cys residues had been replaced and two mutants where three out of four Cys residues were changed into Ala, were characterized regarding their catalytic activities with three different substrates as well as by their binding of three different inhibitors. All three Cys-deficient mutant forms of glutathione transferase M1a-1a were catalytically active with the tested substrates and their binding of inhibitors, measured by I50, were not significantly different from the values previously obtained for the wild-type enzyme. We therefore conclude that none of the Cys residues in this class Mu glutathione transferase are directly involved in the catalysis performed by this enzyme.

Alkylating Agents↗

PubMed1993

Human liver microsomal glutathione transferase. Substrate specificity and important protein sites.

Human liver microsomal glutathione transferase displays the following glutathione peroxidase/transferase activities: dilinoleoylphosphatidylcholine hydroperoxide (0.03 and 0.17 mumol/min.mg, unactivated and N-ethylmaleimide-activated enzyme, respectively), linoleic acid hydroperoxide (0.09 and 0.15 mumol/min.mg), cumene hydroperoxide (0.04 and 3 mumol/min.mg), methyl linoleate ozonide (0.02 and 1.2 mumol/min.mg) and 1-chloro-2,4-dinitrobenzene (1.9 and 24 mumol/min.mg). The activation of glutathione peroxidase activities are much higher than previously observed. The activity towards a phospholipid hydroperoxide is noteworthy since protection against lipid peroxidation has been implied. Methyl linoleate ozonide has not previously been characterised as substrate for any microsomal glutathione transferase. Human liver microsomal glutathione transferase displays an isoelectric point of 9.4 and a structure in agreement with that deduced from the cDNA sequence. Gel electrophoretic analysis shows that proteolytic activation of the human enzyme corresponds to cleavage at Lys-41, thus defining the critical activation site.

Amino Acids↗

PubMed1994

Human glutathione transferase catalysis of the formation of S-nitrosoglutathione from organic nitrites plus glutathione.

The kinetics of spontaneous and human glutathione transferase catalysed formation of S-nitrosoglutathione (GSNO) from glutathione (GSH) and n-butyl- or amyl nitrite have been studied. At physiological pH and temperature, k2 values of 22.3 and 21.0 M-1.min-1 were obtained for n-butyl- and amyl nitrites, respectively. Rate enhancements, (kcat/Km x k2) x 10(-4), due to purified human GSH transferases A1-1, A2-2 and M1a-1a were, respectively, 7.00, 2.94 and 10.6 for n-butyl nitrite and 121, 3.92 and 34.5 for amyl nitrite. GSH transferase P1-1 showed no detectable catalysis of the formation of GSNO. The data suggest that the presence of GSTs A1-1, A2-2 or M1-1 contribute substantially to intracellular metabolism of alkyl nitrites to GSNO. The results may be significant with regard to the immunotoxicity of alkyl nitrites.

Catalysis↗

PubMed1994

Immunogold localization of glutathione transferase B1-1 in Proteus mirabilis.

By using the immunolabelling technique, the cellular localization of glutathione transferase in Proteus mirabilis was investigated. Evidence was obtained indicating a significant higher content of glutathione transferase in the periplasmic than cytoplasmic space. This result further support the idea that bacterial glutathione transferase is involved in xenobiotic detoxication.

Blotting, Western↗

PubMed1984

Isoelectric focusing of brain cortex GSH S-transferase activity in mammals: evidence that polymorphism is absent in man.

Specific activities of GSH S-transferase toward different model substrates were determined in the cytosol prepared from rat, guinea pig, rabbit, mouse, sheep, beef, pig and human brain cortex. The GSH S-transferase composition of the eight mammalian brain cortices was studied by using density gradient isoelectric focusing technique. Human brain cortex GSH S-transferase was resolved into a single peak of activity centered at pH 4.6, whereas the supernatants of all other mammals consisted of more than one enzymatic form. The kinetic properties of all forms isolated were compared.

Adult↗

PubMed1988

Properties of mannosyl- and N-acetylglucosamine-1-phosphate transferases towards dolichol phosphate in liver microsomes from pig embryos.

1. The activity of mannosyl- and N-acetylglucosamine-1-phosphate transferases in microsomes from pig embryonic liver was linear to 1 min of incubation at 37 degrees C. 2. The activity of both enzymes was higher in the presence of Mg2+ as compared to Mn2+. A maximal stimulatory effect of Mn2+ was obtained at 2 mM concentration and greater concentrations of it inhibited the activities of both enzymes. 3. The activity of mannosyl transferase was found to be highest after treatment of microsomes with Nonidet P-40 while the activity of N-acetylglucosamine-1-phosphate transferase was greatest in the presence of sodium deoxycholate. 4. The Km for acceptor substrate was 1.6 x 10(-5)M in the reaction for dolichol phosphate mannose synthesis and 2.2 x 10(-5)M in the reaction for dolichol pyrophosphate N-acetylglucosamine formation. 5. The Km for GDP-mannose was 1.4 x 10(-5)M and for UDP-N-acetylglucosamine-6.2 x 10(-5)M. At saturating concentrations of donor substrates V values (pmol/min/mg) were 1330 and 150, respectively.

Animals↗

PubMed1989

Organic nitrate reductase: reassessment of its subcellular localization and tissue distribution and its relationship to the glutathione transferases.

1. Using a specific and sensitive GLC method for the determination of glyceryl trinitrate (GTN), its subcellular and tissue distribution were reassessed. Liver was the most active tissue, but activity was also detected in the heart, kidney and gut. In all tissues activity was localized in the soluble fraction. The activity of soluble glutathione S-transferase followed the same pattern, liver exhibiting the highest and the heart the lowest activity. 2. Pretreatment with phenobarbitone and 3-methylcholanthrene stimulated both the glutathione S-transferase and organic nitrate reductase activities. 3. Glutathione S-transferase activity was competitively inhibited by GTN. 4. A comparison of the plasma and hepatic metabolism of GTN revealed higher drug affinity for the hepatic enzyme.

Animals↗

PubMed1992

Influence of phospholipid environment on the phosphatidylethanolamine: ceramide-phosphorylethanolamine transferase activity in rat liver plasma membranes.

1. Plasma membranes were treated with phospholipase A2, phospholipase C or phospholipase D. The phosphatidylethanolamine:ceramide-phosphorylethanolamine transferase was deactivated by phospholipase C treatment, whereas phospholipase A2 and phospholipase D did not affect the enzyme. 2. Incorporation of phosphatidylethanolamine and phosphatidylglycerol into partially delipidated plasma membranes resulted in significant stimulation of the transferase, whereas inclusion of sphingomyelin and phosphatidylserine suppressed the enzyme activity. Our results suggest that phosphatidylserine is a regulator of sphingomyelin level in membranes. 3. The activity of phosphatidylethanolamine:ceramide-phosphorylethanolamine transferase was not influenced by the fluidity of its lipid environment.

Animals↗

PubMed1994

Examination of glutathione S-transferase isoenzyme profiles in human liver using high-performance affinity chromatography.

A method for the examination of the glutathione S-transferase isoenzyme profiles in human liver using a new HPLC affinity support is described. Liver cytosol was injected directly onto an HPLC column (5 x 0.46 cm) containing a support with a covalently bound affinity ligand (S-octylglutathione) specific for the isoenzymes. Contaminating cytosolic proteins were removed in a washing step. The isoenzymes were eluted with a linear gradient of a different affinity ligand in the mobile phase. Coinciding with the affinity ligand gradient, a salt gradient (0-200 mM sodium chloride) was applied. In this manner the isoenzymes were fractionated into the enzymatically active homodimers and heterodimers. The classes of the affinity fractionated isoenzymes were determined by SDS-PAGE and ELISA while the subunit content was determined by reversed-phase chromatography. For one liver three Alpha class isoenzyme subunits, forming three heterodimers and two homodimers, were detected. Five livers were examined, and the homodimer A1-1 was found to be the predominant glutathione S-transferase isoenzyme. Minor amounts of Pi and Mu class isoenzymes were also detected. This non-denaturing high-performance affinity chromatography method reduced analysis time by a factor of ten when compared to other affinity analysis methods for the glutathione S-transferases.

Chromatography, Affinity↗

PubMed1980

Glutathione and glutathione S-transferases in the Salmonella mammalian-microsome mutagenicity test.

Levels of the tripeptide glutathione (GSH) and the activity of glutathione S-transferases were investigated in S9 fractions of rats and mice and in Salmonella typhymurium tester strains TA1535, TA100, TA1538 and TA98. The S9 and Salmonella typhimurium tester strains had high levels of glutathione. Compared with S9, the activity of GSH S-transferases was lower in the bacteria. However, electrophiles such as 1-chloro-2,4-dinitrobenzene (CDNB), diethyl maleate and styrene oxide were effectively bound to bacterial GSH. The mutagenicity of the direct mutagen CDNB was drastically lowered in presence of S9 fractions but not in presence of microsomes. A comparable decrease was obtained when microsomal supernatant, which contains GSH and GSH S-transferases, was added to the microsomes. Addition of GSH in excess completely abolished mutagenicity of CDNB. These results demonstrate that the conjugation of electrophiles with GSH mediated by the S9 fraction or the bacterial tester strains represents an important detoxication mechanism which may influence the results obtained with the Salmonella typhimurium mammalian-microsome mutagenicity test.

Animals↗

PubMed1987

Patterns of epoxide metabolism by epoxide hydrolase and glutathione S-transferase associated with age and genotype in Drosophila melanogaster.

Epoxide hydrolase and glutathione S-transferase activities toward trans- and cis-stilbene oxides were measured in 3 strains of Drosophila melanogaster. Differences in age dependence, substrate selectivity and subcellular location were detected suggesting the presence of multiple forms of these enzymes. In addition, interstrain differences indicate the presence of genetic variation for epoxide hydrolase and glutathione transferase activities. These results illustrate a potential use of these assays in D. melanogaster to complement existing tests (e.g. recessive lethal tests or Ames assays) for evaluating the relationship between epoxide hydrolase and glutathione S-transferase levels and the genotoxicity of epoxides.

Aging↗

PubMed1984

Differential activation and inhibition of different forms of rat liver glutathione S-transferase by the herbicides 2,4-dichlorophenoxyacetate (2,4-D) and 2,4,5-trichlorophenoxyacetate (2,4,5-T).

The predominant forms of the dimeric enzyme glutathione S-transferase were purified from rat liver. Forms YbY'b and YbYb (also known as forms C and A, respectively) could be almost completely inhibited by 2,4-dichlorophenoxyacetate (2,4-D). Half-maximal inhibition was obtained at 0.5 mM 2,4-D. Inhibition was seen even at extrapolated infinite concentrations of both substrates for YbYb but not YbY'b. These same forms could also be inhibited 70 to 80% by 2,4,5-trichlorophenoxyacetate (2,4,5-T) with half maximal inhibition occurring at 0.2 mM. Glutathione S-transferase form YaYa was maximally inhibited by 72 and 30%, respectively, by 2,4-D and 2,4,5-T. The 30% inhibition of YaYa caused by 2,4,5-T was shown to reduce the nearly complete inhibition caused by a previously characterized inhibitor, namely bile acids. This suggests competition for a common binding site on the enzyme. In contrast to the above results, it was found that form YcYc (also termed AA) was activated 2.7-fold by 2,4,5-T and 1.4-fold by 2,4-D. This activation could be blocked by chenodeoxycholate which, by itself, did not affect the activity of the enzyme. The effects of 2,4,5-T and 2,4-D on the heterodimer YaYc (also termed form B) were intermediate between their effects on YaYa and YcYc, suggesting that each subunit contributes its unique property to the heterodimer. The microsomal membrane-bound form of glutathione S-transferase was also examined and found to be inhibited by both 2,4-D and 2,4,5-T. However, unlike the inhibitions of soluble forms, 2,4,5-T caused more extensive inhibition than 2,4-D.(ABSTRACT TRUNCATED AT 250 WORDS)

2,4,5-Trichlorophenoxyacetic Acid↗

PubMed1985

Inhibition of human glutathione S-transferases by 2,4-dichlorophenoxyacetate (2,4-D) and 2,4,5-trichlorophenoxyacetate (2,4,5-T).

The phenoxyacid herbicides, 2,4-dichlorophenoxyacetate (2,4-D) and 2,4,5-trichlorophenoxyacetate (2,4,5-T), inhibit all known isoenzymes of human liver and erythrocyte glutathione (GSH) S-transferase. However, the maximal inhibition and the I50 values vary significantly for different isoenzymes. GSH peroxidase II activity of GSH S-transferases is also inhibited by both these compounds. These studies suggest that the effect of these compounds on human GSH S-transferases is significantly different from that reported for rat liver enzymes.

2,4,5-Trichlorophenoxyacetic Acid↗