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Biomedical subjects

F Oesch

Publications and source records attributed to F Oesch.

At least 325 records · Page 18Linked to original sources
PubMed1985

Regulation and expression of four cytochrome P-450 isoenzymes, NADPH-cytochrome P-450 reductase, the glutathione transferases B and C and microsomal epoxide hydrolase in preneoplastic and neoplastic lesions in rat liver.

Nitrosamine-induced hepatocarcinogenesis has been used to investigate the regulation and expression of different drug-metabolizing enzymes in preneoplastic and neoplastic lesions in the female Wistar rat. The enzymes investigated were two phenobarbital-inducible cytochrome P-450 (cyt. P-450) isoenzymes (PB1 and PB2, mol. wt. 52 000 and 53 500, respectively), two 3-methylcholanthrene-inducible forms (MC1 and MC2, mol. wt. 54 500 and 57 000, respectively), NADPH-cytochrome P-450 reductase, the cytosolic glutathione transferases (GSTs) B and C and the microsomal epoxide hydrolase with broad substrate specificity (mEHb). Carcinogen-induced lesions were identified by use of the known markers of hepatocarcinogenesis adenosinetriphosphatase and gamma-glutamyl transpeptidase. While the GSTs and mEHb were increased in all preneoplastic and neoplastic lesions, the levels of the individual cyt. P-450 isoenzymes were characteristically different from each other. In many of the early ATPase deficient islets PB1 was elevated, whereas the content of the other cyt. P-450 forms and NADPH-cytochrome P-450 reductase was either unchanged or slightly lowered. At later stages of hepatocarcinogenesis PB1 returned to the levels of the surrounding tissue, while the other cyt. P-450 isoenzymes were decreased, the most prominent reduction being found in MC1. In neoplastic nodules all the cyt. P-450s and NADPH-cyt. P-450 reductase were diminished, some of them dramatically. These findings indicate that in spite of a common response of groups of P-450s to inducing agents, individual P-450 isoenzymes are also regulated separately. Moreover, the constant elevation of mEHb and GSTs in all lesions investigated in this study demonstrates that these enzymes, which are largely involved in deactivation, are regulated in a different fashion from the predominantly carcinogen-activating monooxygenases. The observed differences in enzyme pattern may provide a useful method for subdividing and categorizing preneoplastic and neoplastic lesions.

Animals↗
PubMed1985

Interaction of tetrachlorobiphenyls with isolated rat liver mitochondria.

A comparative study of the effects of tetrachlorobiphenyls (TCBs) on the succinate-supported respirations of rat liver mitochondria was made, and some differences in effects caused by the different chlorine positions of the biphenyl rings were clarified. The inhibitory actions of 2,3,2',3'-,2,4,2',4'-, and 2,5,2',5'-TCBs on both state 3 and uncoupler-stimulated respirations were potent, while those induced by 2,6,2',6'-, and 3,4,3',4'-TCBs were weak. 2,3,2',3'-,2,4,2',4'-,2,5,2',5'-, and 2,6,2',6'-TCBs stimulated state 4 respiration, but 3,4,3',4'-TCB had very little effect on this respiration. The latent adenosine triphosphatase activity was stimulated by 2,3,2',3'-,2,4,2',4'-, and 2,5,2',5'-TCBs, but 2,6,2',6'-, and 3,4,3',4'-TCBs had no effects. The relationship between these effects and chemical structure of TCBs is discussed.

Adenosine Triphosphatases↗
PubMed1985

Metabolism of benzo(a)pyrene by subcellular fractions of rat liver: evidence for similar patterns of cytochrome P-450 in rough and smooth endoplasmic reticulum but not in nuclei and plasma membrane.

Since our earlier work (P. Stasiecki, F. Oesch, G. Bruder, E.D. Jarasch, and W.W. Franke, Eur. J. Cell Biol., 21: 79-92, 1980) had shown that carcinogen-metabolizing monooxygenase activity was present in almost all investigated cellular membranes, the possibility of differential control of the various metabolic pathways in the individual cellular membranes arose. Using high pressure liquid chromatography we have now studied the benzo(a)pyrene metabolites formed by rough and smooth endoplasmic reticulum, nuclei, and plasma membrane as well as mitochondrial fractions and investigated the metabolic cooperation between the monooxygenases and epoxide hydrolase in these fractions. Since various cytochrome P-450 isozymes catalyze the oxidative attack on the benzo(a)pyrene molecule at defined preferential sites, this analysis also provides an indirect trace of potential differences in the pattern of cytochrome P-450 isozymes present in the individual membranes. The metabolic profiles produced by the two most active fractions, smooth and rough endoplasmic reticulum, were very similar to each other but different from those produced by the other three preparations. The metabolite pattern produced by incubations containing nuclear fractions differed slightly from that produced by the fractions of endoplasmic reticulum, but plasma membrane and mitochondria produced markedly different patterns. Since the similarity of the benzo(a)pyrene metabolite pattern produced by the smooth and rough endoplasmic reticulum suggested similar cytochrome P-450 isozyme patterns in these two subfractions, they were further investigated by the use of selective inducers as well as a broad spectrum substrate, 7-ethoxy-coumarin, in the absence and presence of selective inhibitors. Treatment of animals with trans-stilbene oxide or phenobarbital (a) increased the total amount of metabolites per protein mass and time, (b) changed the pattern of metabolites, but (c) induced a pattern of metabolites which was again very similar in rough and smooth endoplasmic reticulum. Even more distinct changes were found following treatment with 3-methylcholanthrene or beta-naphthoflavone. Both of these compounds (a) preferentially induced the activity of rough endoplasmic reticulum, (b) changed the profile of metabolites, but (c) again did not disturb the similarities of the benzo(a)pyrene metabolite pattern between both fractions.(ABSTRACT TRUNCATED AT 400 WORDS)

7-Alkoxycoumarin O-Dealkylase↗
PubMed1985

Activation of N-acetoxy- and N-hydroxy-2-acetylaminofluorene to mutagenic and cytotoxic metabolites by V79 Chinese hamster cells.

N-Acetoxy-2-acetylaminofluorene (AAAF) and N-hydroxy-2-acetylaminofluorene (OH-AAF) are mutagenic to V79 cells, causing the induction of 6-thioguanine-resistant clones, and are cytotoxic. The presence of the deacetylase inhibitor, paraoxon, drastically reduces both the mutagenic and cytotoxic effects. This strongly suggests that deacetylated metabolites are the major active species. Furthermore, when Salmonella typhimurium TA98 is used as target organism, addition of homogenate of V79 cells strongly potentiates the mutagenicity of OH-AAF. To our knowledge, this is the first report demonstrating a significant biological effect due to the metabolism of a mutagen by V79 cells.

2-Acetylaminofluorene↗
PubMed1985

Arene imines, a new class of exceptionally potent mutagens in bacterial and mammalian cells.

K-region aziridines of polycyclic aromatic hydrocarbons reverted Salmonella typhimurium his- (TA100, TA98) and Escherichia coli trp- strains (WP2 uvrA), without requiring activation by mammalian enzymes. The number of revertants induced per nmol in S. typhimurium TA 100, the most responsive strain, variea from 6 to 10,000 for the seven monoaziridines and the two bisaziridines tested. Interestingly, the mutagenic potencies (y) of the monoaziridines were closely related (r = 0.984) with those of the corresponding epoxide analogues (x) by the equation y = 19.6 X0.97, i.e., the aziridines were about 20-fold stronger mutagens than were the epoxides. One of the aziridines, benzo(a)pyrene (BP)-4,5-imine, was investigated in several additional mutagenicity test systems: toxicity in DNA repair-deficient (rec-) and -proficient (rec+) Bacillus subtilis strains; induction of 6-thioguanine resistance in V79 Chinese hamster cells; and induction of sister chromatid exchanges in cultured human fibroblasts. In all systems, BP-4,5-imine was much more active than the epoxide analogue, BP-4,5-oxide. The difference in activity was particularly large in the two test systems with mammalian target cells in which several hundredfold higher concentrations of the epoxide had to be used in order to elicit equipotent effects. Even r-7,t-8-dihydroxy-t-9,10-oxy-7,8,9,10-tetrahydro-BP, which is one of the most potent mutagens known for V79 cells, was less active in the mammalian cells than was BP-4,5-imine. One reason that arene imines are such potent mutagens may be that they are poorly detoxified. Addition of highly purified microsomal epoxide hydrolase, which strongly reduced the mutagenicity of BP-4,5-oxide and benz(a)anthracene-5,6-oxide in S. typhimurium, had no effect on the mutagenicity of the corresponding aziridines. Furthermore, while benz(a)anthracene-5,6-oxide was inactivated by highly purified cytosolic epoxide hydrolase, benz(a)anthracene-5,6-imine was not inactivated. It is noteworthy that the arene imines are isomeric with and structurally closely related to aromatic amines. Some aziridines derived from nonaromatic structures (ethylene imines) have been reported as metabolites of xenobiotics; others are used as chemotherapeutics. At present, however, the results are mainly of theoretical interest in that a new type of arene derivatives with exceptionally potent, probably ultimate, mutagenicity was discovered and may be exploited for the study of mechanisms of chemical carcinogenesis.

Animals↗
PubMed1984

Phosphorylation of rabbit liver cytochrome P-450 LM2 and its effect on monooxygenase activity.

The phosphorylation of rabbit liver microsomal cytochrome P-450 LM2 by catalytic subunit of cyclic AMP-dependent protein kinase (W. Pyerin et al. (1983) Carcinogenesis 4, 573) has now been studied in detail with purified soluble form of cytochrome P-450 as well as with the purified protein incorporated into model membranes. The apparent Km values for P-450 of the phosphorylation reaction in all experimental systems were in a range of 2-8 microM, while the Vmax values were dependent on the state of P-450. Upon phosphorylation, the reconstituted enzyme activities with benzphetamine (N-demethylation) and 7-ethoxycoumarin (O-deethylation) as substrates were reduced to 30-40% of control.

Animals↗
PubMed1984

Identity of dihydrodiol dehydrogenase and 3 alpha-hydroxysteroid dehydrogenase in rat but not in rabbit liver cytosol.

Dihydrodiol dehydrogenase and 3 alpha-hydroxysteroid dehydrogenase activity in rat and rabbit liver cytosol have been analyzed by isoelectric focussing and subsequent activity staining. Identity of the two enzymes in rat liver cytosol is demonstrated. At least 4 main enzyme forms possessing dihydrodiol dehydrogenase activity can be detected in rabbit liver cytosol. However, in this species, only one of these forms has measurable activity towards 3 alpha-hydroxysteroids.

3-Hydroxysteroid Dehydrogenases↗
PubMed1984

Drug metabolism in man and its relationship to that in three rodent species: monooxygenase, epoxide hydrolase, and glutathione S-transferase activities in subcellular fractions of lung and liver.

Activities of drug metabolizing enzymes were determined in subcellular fractions of lung biopsies from 12 human subjects and in liver biopsies from 15 other human subjects. Monooxygenase (MO) activity with 7-ethoxycoumarin as a substrate and epoxide hydrolase (EH) activity with benzo[a]pyrene 4,5-oxide as a substrate were measured in the microsomal fraction, glutathione S-transferase (GST) activity toward 2,4-dinitrochlorobenzene in the cytosolic fraction. MO activity was further characterized by the use of inhibitors known to act preferentially on different MO forms. To facilitate extrapolations from test results obtained in animals to man enzyme activities were also determined in corresponding fractions from commonly used laboratory animals, Sprague-Dawley rat, NMRI mouse, and Syrian golden hamster. All investigated specific activities were lower in lung than in liver preparations by factors ranging from 2.4 to 7 in the mouse, 4 to 18 in rat and hamster, and 11 to 697 in man. The high ratio between liver and lung activity in man occurred with MO and is due to an extremely low activity in human lung. It is not clear whether this low activity is predominantly due to low amounts of enzyme or to inhibitors known to be present in human lung preparations. With this exception of human lung MO, species differences in the investigated enzyme activities were moderate. Among the three rodent species, rat was most similar to man, with none of the investigated activities differing by a factor more than 2. The mouse differed from these two species by considerably higher MO and GST activities in both organs, and by a relatively low EH activity in liver for the investigated substrates, while the hamster displayed comparatively high lung GST and EH and liver GST and MO activities. MO inhibition patterns by different in vitro inhibitors were similar in the same organs of different species, but differed in lung and liver. Standard concentrations of the diagnostic inhibitors led to preferential inhibition of lung MO by metyrapone and considerably less by tetrahydrofuran, while for liver MO the reverse was true. In both organs, the standard concentration of alpha-naphthoflavone had only very weak effects. In conclusion, man and commonly used laboratory rodents are not grossly different with respect to the investigated enzyme activities with the possible exception of lung MO. For the substrates investigated, the rat represented clearly the best model for man among the studied animal species.

Adult↗
PubMed1984

Existence of multiple forms of microsomal epoxide hydrolases with radically different substrate specificities.

Evidence for the existence in rat and rabbit liver of two microsomal epoxide hydrolases with radically different substrate specificities was obtained, one with a broad specificity (EHb), whilst the other catalyzed the hydrolysis of cholesterol 5 alpha,6 alpha-oxide (EHch), a reaction taken as diagnostic since it was not observed with pure fractions of EHb. The two enzymes were physically separated by immunoprecipitation using antibodies which had been raised against EHb purified to apparent homogeneity. The substrate specificity of the two enzymes is radically different and mutually complementary. Cholesterol 5 alpha,6 alpha-oxide has a trisubstituted oxirane ring. All epoxides of this nature tested to date were not, or very poor, substrates of EHb. The two enzymes can also effectively be discriminated by inhibitors, in that 5 alpha,6 alpha-imino-5 alpha-cholestane-3 beta-ol potently inhibits EHch but not EHb whilst 1,1,1-trichloropropene oxide has the opposite specificity. The cytosolic EH did not significantly contribute to the catalysis of the hydrolysis of cholesterol 5 alpha,6 alpha-oxide.

Animals↗
PubMed1984

Characterization, localization and regulation of a novel phenobarbital-inducible form of cytochrome P450, compared with three further P450-isoenzymes, NADPH P450-reductase, glutathione transferases and microsomal epoxide hydrolase.

Two cytochromes P450 (PB1 and PB2) have been isolated from the livers of rats treated with phenobarbital. PB2 (mol. wt. 53 500) is novel and is the first example of a phenobarbital-inducible enzyme with a Soret peak at 447 nm. Using an enzyme-linked immunosorbent assay, some immunochemical and structural similarities were observed between these cytochromes. PB1 and PB2 were induced by phenobarbital, Aroclor 1254, trans-stilbene oxide and to a lesser extent by isosafrole. Immunohistochemical localization of these proteins in the liver of untreated rats showed PB1 to be localized in a large area and PB2 in a narrow range of cells around the central vein. This demonstrates the heterogeneity of hepatocytes even within the centrilobular area and indicates that the synthesis of these two proteins is regulated differently although both are induced by the same agent, phenobarbital. Two 3-methylcholanthrene inducible cytochromes MC1 (mol. wt. 54 500) and MC2 (mol. wt. 57 000) were present at very low levels, MC2 mostly in the periportal region but also diffusely distributed throughout the lobule including some centrilobular cells, MC1 concentrated in the centrilobular region. The localization of two major groups of glutathione transferases (GST's) was also different. 'C' type proteins (Yb Yb') and microsomal epoxide hydrolase (EH), were concentrated around the central vein, whereas the 'B' type proteins (Ya Yc) and cytochrome P450 reductase were distributed in a larger area of this region. Thus, the localization was different for some members of the same enzyme family, whilst similarities in the localization existed across the border of the families: (i) PB2, MC1, EH and GST 'C' type proteins were concentrated in a narrow area around the central vein; (ii) PB1 and GST 'B' type proteins occupied a large centrilobular area; (iii) MC2 levels were very low, predominantly periportal but also diffusely distributed throughout the lobule. Treatment of the animals with inducers increased the staining intensity and in several cases extended the areas of cells containing these proteins over the adjacent zone without fundamentally altering their distributions. However, treatment with beta-naphthoflavone led to a shift of MC1 to the periportal area. This suggests that the expression of these proteins in certain cells is not an irreversible quality of differentiation but depends on the degree of suppression and derepression of regulatory components.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Differential regulation of two microsomal epoxide hydrolases in hyperplastic nodules from rat liver.

Two microsomal epoxide hydrolases of the rat liver were found to be differentially regulated in hyperplastic nodules. Whilst the activity for substrates of the well-known microsomal epoxide hydrolase with a broad substrate specificity (EHb), benzo[a]pyrene 4,5-oxide and androstene oxide (16 alpha, 17 alpha-epoxyandrosten-3-one), was greatly (approximately 5-fold) increased in the nodule microsomes and moderately (approximately 2-fold) increased in the surrounding tissue, that for the substrate of the novel microsomal epoxide hydrolase, cholesterol 5 alpha,6 alpha-oxide (EHch) remained unchanged. Since both enzymes convert endogenous steroid epoxides but with distinct structural features, this differential regulation may indicate a role of endogenous steroid epoxide(s) of a defined structure during hepatocarcinogenesis. Alternatively, this differential regulation may serve as a marker during hepatocarcinogenesis.

Animals↗
PubMed1984

Metabolism of carcinogens, possibilities for modulation.

One of the structural elements which are widely occurring in very many chemical mutagens and carcinogens are aromatic and olefinic moieties. These can be transformed into epoxides by microsomal monooxygenases. Such epoxides may spontaneously react with nucleophilic centers in the cell and thereby covalently bind to DNA, RNA and protein. Such a reaction may lead to cytotoxicity, allergy, mutagenicity and/or carcinogenicity, depending on the properties of the epoxide in question. An important contributing factor is the presence of enzymes controlling the concentration of such epoxides. There are several microsomal monooxygenases which differ in activity and substrate specificity. With large substrates, some monooxygenases preferentially attack at one specific site different from that attacked by others. Some of these pathways lead to reactive products, others are detoxification pathways. Also important are the enzymes which metabolize epoxides, such as epoxide hydrolases and glutathione transferases. Such enzymes can act as inactivating and in some specific cases also as co-activating enzymes. Moreover, precursor-sequestering enzymes such as dihydrodiol dehydrogenase, glucuronosyl transferases and sulphotransferases are important for the control of reactive epoxides. These enzymes themselves are subject to control by many endogenous and exogenous factors. By virtue of their contribution to the control of carcinogenic metabolites such modulators can act as modifiers of tumorigenesis and can be used experimentally to study the role of the various individual enzymes.

Animals↗
PubMed1984

Significance of various enzymes in the control of mutagenic and carcinogenic metabolites derived from aromatic structures.

One important early contribution to the control of chemical carcinogenesis is provided by the enzyme pattern responsible for the generation and disposition of reactive metabolites. Especially well studied is the important group of enzymes responsible for the control of reactive epoxides. Many natural as well as man-made foreign compounds, including pharmaceuticals, possess olefinic or aromatic double bonds. Such compounds can be transformed to epoxides by microsomal monooxygenases present in very many mammalian organs. By virtue of their electrophilic reactivity such epoxides may spontaneously react with nucleophilic centers in the cell and thus covalently bind to DNA, RNA, and protein. Such alterations of critical cellular macromolecules may disturb the normal biochemistry of the cell and lead to cytotoxic, allergenic, mutagenic, and/or carcinogenic effects. Whether such effects will be manifested depends on one hand on the chemical reactivity as well as other properties (geometry, lipophilicity) of the epoxide in question. On the other hand, enzymes controlling the concentration of such epoxides are another important contributing factor. Several microsomal monooxygenases exist differing in activity and substrate specificity. With respect to large substrates, some monooxygenases preferentially attack at one specific site different from that attacked by others. Some of these pathways lead to reactive products, others are detoxification pathways. Moreover, enzymes metabolizing such epoxides represent a further determining factor. These enzymes include epoxide hydrolases and glutathione transferases. These enzymes do not play a pure inactivating role, but can in some cases also act as coactivating enzymes. Enzymes involved in biosynthesis and further metabolism of epoxides differ in quantity and sometimes also in substrate specificity between organs, developmental stages, sexes, and animal species.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcohol Oxidoreductases↗
PubMed1984

Dose dependent activation of rat small intestinal monooxygenase-activity towards benzo(a)pyrene and 7-ethoxycoumarin after oral pretreatment with cimetidine.

Arylhydrocarbon-hydroxylase and 7-ethoxycoumarin O-deethylase were stimulated in intestinal microsomes prepared two hours after administration of cimetidine (25 mg/kg, p.o.) to male Wistar rats. Moreover, the metabolite-pattern of benzo(a)pyrene was changed as compared to that in control (saline, 2 hr) animals. Cytochrome P-450 content was not affected. However, rats receiving higher doses of cimetidine (75 and 150 mg/kg) showed a dose dependent decrease in diolformation from benzo(a)pyrene. We were not able to achieve similar effects on monooxygenase activity by in vitro pretreatment of intestinal cells and/or microsomes. Observed interaction might implicate an effect of cimetidine on carcinogenic activity in small intestine of polycyclic aromatic hydrocarbons.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1984

Metabolism of genotoxic agents: control of reactive epoxides by hydrolase and transferase reactions.

Hydrolase and transferase reactions play dual roles in the control of carcinogenic and mutagenic species. In some instances, they play an activating or coactivating role. However, as far is known, in most cases they are wholly or predominantly inactivating mechanisms. The important hydrolase and transferase enzymes that are involved in the control of reactive epoxides are particularly well studied. These include epoxide hydrolases and glutathione transferases that react directly with electrophilic epoxides, as well as conjugating enzymes, such as glucuronosyl transferases and sulfotransferases, that sequester nucleophilic precursors of complex epoxides such as phenols and dihydrodiols. These, and other enzymes that are involved in biosynthesis and the further metabolism of reactive metabolites, are an important contributing factor to differences in susceptibility, since they differ in quantity and, sometimes, also in substrate specificity between organs, developmental stages, sexes and animal species. Knowledge of these variables is, therefore, required for a rational extrapolation to humans of the toxicity data obtained in available test systems; the rational interpretation of data obtained by biomonitoring requires similar knowledge.

Alcohol Oxidoreductases↗
PubMed1983

Identification and characterization of a new epoxide hydrolase from mouse liver microsomes.

A new microsomal epoxide hydrolase (mEH2) has been identified and characterized. This enzyme has properties which distinguish it from previously described cytosolic (cEH) or membrane-bound (mEH1) epoxide hydrolases. The enzyme is an integral microsomal protein which is not dissociated from the membrane by repeated washing, high ionic strength salt, or chaotropic agent solutions, or by sonication. It is very different from the normally described microsomal epoxide hydrolase (mEH1) as shown by its different substrate specificity and kinetic properties and by immunological criteria. In contrast to the hitherto described microsomal epoxide hydrolase, mEH1, the new enzyme effectively catalyzes the hydration of transdisubstituted oxiranes such as trans-stilbene oxide and trans-beta-ethyl styrene oxide and has no appreciable activity toward benzo(a)pyrene 4,5-oxide. It is also structurally distinct, in that it does not cross-react with antibodies raised against the normally described microsomal epoxide hydrolase mEH1. This newly described microsomal epoxide hydrolase probably represents an important factor in the control of reactive epoxides; its location in the membrane ensures access to lipophilic epoxides generated by membrane-bound monooxygenases, and its substrate specificity is such that it can hydrolyze epoxides poorly metabolized by the previously described microsomal epoxide hydrolase.

Animals↗
PubMed1983

Purification and characterization of a new cytosolic glutathione S-transferase (glutathione S-transferase X) from rat liver.

A hitherto unknown cytosolic glutathione S-transferase from rat liver was discovered and a method developed for its purification to apparent homogeneity. This enzyme had several properties that distinguished it from other glutathione S-transferases, and it was named glutathione S-transferase X. The purification procedure involved DEAE-cellulose chromatography, (NH4)2SO4 precipitation, affinity chromatography on Sepharose 4B to which glutathione was coupled and CM-cellulose chromatography, and allowed the isolation of glutathione S-transferases X, A, B and C in relatively large quantities suitable for the investigation of the toxicological role of these enzymes. Like glutathione S-transferase M, but unlike glutathione S-transferases AA, A, B, C, D and E, glutathione S-transferase X was retained on DEAE-cellulose. The end product, which was purified from rat liver 20 000 g supernatant about 50-fold, as determined with 1-chloro-2,4-dinitrobenzene as substrate and about 90-fold with the 1,2-dichloro-4-nitrobenzene as substrate, was judged to be homogeneous by several criteria, including sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, isoelectric focusing and immunoelectrophoresis. Results from sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and gel filtration indicated that transferase X was a dimer with Mr about 45 000 composed of subunits with Mr 23 500. The isoelectric point of glutathione S-transferase X was 6.9, which is different from those of most of the other glutathione S-transferases (AA, A, B and C). The amino acid composition of transferase X was similar to that of transferase C. Immunoelectrophoresis of glutathione S-transferases A, C and X and precipitation of various combinations of these antigens by antisera raised against glutathione S-transferase X or C revealed that the glutathione S-transferases A, C and X have different electrophoretic mobilities, and indicated that transferase X is immunologically similar to transferase C, less similar to transferase A and not cross-reactive to transferases B and E. In contrast with transferases B and AA, glutathione S-transferase X did not bind cholic acid, which, together with the determination of the Mr, shows that it does not possess subunits Ya or Yc. Glutathione S-transferase X did not catalyse the reaction of menaphthyl sulphate with glutathione, and was in this respect dissimilar to glutathione S-transferase M; however, it conjugated 1,2-dichloro-4-nitrobenzene very rapidly, in contrast with transferases AA, B, D and E, which were nearly inactive towards that substrate.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acids↗