Search PubMed⌕ Search

Biomedical subjects

B Ketterer

Publications and source records attributed to B Ketterer.

At least 37 records · Page 2Linked to original sources
PubMed1995

Forward and reverse catalysis and product sequestration by human glutathione S-transferases in the reaction of GSH with dietary aralkyl isothiocyanates.

The reversible reaction of GSH with two dietary anticarcinogens, benzyl isothiocyanate (BITC) and phenethyl isothiocyanate (PEITC), has been studied in the absence and presence of human glutathione S-transferases (GSTs). The spontaneous reaction at pH 7.4 and 37 degrees C yielded values for k2 of 17.9 and 6.0 M-1.s-1 for GSH conjugation of BITC and PEITC respectively (forward reaction), and k1 values of 6.9 x 10(-4) and 2.4 x 10(-4) s-1 for dissociation of the respective GSH conjugates, BITC-SG and PEITC-SG (reverse reaction). GSTs A1-1, A2-2, M1a-1a and P1-1 catalysed both the forward and reverse reactions with specific activities (mumol/min per mg at 30 microM isothiocyanate or GSH conjugate) ranging from 23.1 for the GSH conjugation of BITC by GST P1-1 to 0.03 for the dissociation of BITC-SG by GST A1-1. When present at similar concentration to substrates (12 microM), GSTs A1-1 and A2-2 but not GST M1a-1a shifted the equilibrium in favour of BITC-SG or PEITC-SG. Kinetic studies confirmed that GST A1-1 interacted selectively with the GSH conjugates in the micromolar range (Km 6.9 microM, Ki 4.3 microM), whereas GST M1a-1a interacted with BITC-SG and PEITC-SG with approx. 5-fold lower affinity. In conclusion, GSTs are true catalysts; at high intracellular concentration they also sequester GSH conjugates, promoting GSH conjugation, whereas trace extracellular GSTs promote dissociation of effluxed organic isothiocyanate-GSH conjugates.

Anticarcinogenic Agents↗
PubMed1995

Expression and polymorphism of glutathione S-transferase in human lungs: risk factors in smoking-related lung cancer.

The relationships between smoking and the expression of glutathione S-transferase (GST*) isozymes GSTM1-1, GSTM3-3, GSTP1-1 and GSTA1-1/2-2 (GSTA1/2), or between smoking and activities of epoxide hydrolase (EH) and aryl hydrocarbon hydroxylase (AHH) were investigated in lung samples from 27 patients with lung cancer and 11 control patients by immunoblot analysis and enzyme assays. Determination of genotypes in blood leucocyte DNA showed that possession of the mu-class GSTM1 gene was closely related to the expression of GSTM1-1 and GSTM3-3 enzymes in lung cytosol: patients with the GSTM1 null genotype had no detectable GSTM1 protein and less GSTM3 protein than patients with the GSTM1 gene (P < 0.001). Absence of the GSTM1 gene did not affect the content of phi-class GSTP1-1 or alpha-class GSTA1/2. GST activity towards 1-chloro-2,4-dinitrobenzene was lower (P < 0.01) in patients lacking the GSTM1 gene than in those expressing GSTM1; in general, patients with a low GSTM3-3, GSTP1-1 or GSTA1/2 content also had significantly less overall GST activity. The pulmonary content of GSTP1-1 was greater in cancer than in non-cancer patients (P < 0.05). Smoking did not influence the levels of GST isozymes or the EH activity. In contrast, the AHH activity was significantly (P < 0.01) increased by smoking. Neither AHH nor EH showed a correlation with GSTM1 polymorphism. Our data support the idea that in smokers who lack the GSTM1 gene, activation of carcinogens in tobacco smoke (e.g. benzo[alpha]pyrene) is increased, while the efficacy of detoxification is limited both qualitatively (absence of GSTM1-1 enzyme and low expression of GSTM3-3 enzyme) and quantitatively (low overall GST activity). This imbalance in the metabolism of carcinogens may explain the increased susceptibility to lung cancer reported in smokers with the GSTM1 null genotype.

Animals↗
PubMed1995

Conjugation of carcinogens by theta class glutathione s-transferases: mechanisms and relevance to variations in human risk.

Conjugation of chemicals with glutathione (GSH) can lead to decreased or increased toxicity. A genetic deficiency in the GSH S-transferase mu class gene M1 has been hypothesized to lead to greater risk of lung cancer in smokers. Recently a gene deletion polymorphism involving the human theta enzyme T1 has been described: the enzyme is present in erythrocytes and can be readily assayed. A rat theta class enzyme, 5-5, has structural and catalytic similarity and the protein was expressed in the Salmonella typhimurium tester strain TA1535. Expression of the cDNA vector increased the mutagenicity of ethylene dibromide and several methylene dihalides. Mutations resulting from the known GSH S-transferase substrate 1,2-epoxy-3-(4'nitrophenoxy)propane were decreased in the presence of the transferase. Expression of transferase 5-5 increased mutations when 1,2,3,4-diepoxybutane (butadiene diepoxide), 4-bromo-1,2-epoxybutane, or 1,3-dichloracetone were added. The latter compound is a model for the putative 1,2-dibromo-3-chloropropane oxidation product 1-bromo-3-chloroacetone. These genotoxicity and genotyping assays may be of use in further studies of the roles of GSH S-transferase theta enzymes in bioactivation and detoxication and any changes in risk due to polymorphism.

Animals↗
PubMed1994

Effects of human and rat glutathione S-transferases on the covalent DNA binding of the N-acetoxy derivatives of heterocyclic amine carcinogens in vitro: a possible mechanism of organ specificity in their carcinogenesis.

The effects of glutathione (GSH) and of purified human and rat GSH S-transferases (GSTs) on the covalent DNA binding of 3 putative ultimate food-borne carcinogens, the N-acetoxy derivatives of 2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP), 2-amino-3-methylimidazo(4,5-f)quinoline (IQ), and 2-amino-3,8-dimethylimidazo(4,5-f)quinoxaline (MeIQx), were studied in vitro. GSH (5 mM) alone slightly inhibited (10%) the DNA binding of N-acetoxy-PhIP (100 microM) at pH 7.5, but the binding could be strongly inhibited in the presence of both GSH and GSTs. Among human GSTs, the isozyme A1-1 (alpha-class) was most effective (90% inhibition) followed by A1-2 (40% inhibition); the effect of adding A2-2 was negligible, suggesting that the activity exists in subunit A1. In addition, human GST P1-1 (pi-class) also had some inhibitory effect (30%). Among the rat GSTs tested, GST 1-2 and GST 12-12 (theta-class), which are the equivalent of human A1-2 and T2-2, respectively, were able to inhibit DNA binding of N-acetoxy-PhIP (75 and 40%, respectively). This activity toward N-acetoxy-PhIP was dependent on enzyme concentration and was subject to inactivation by triethyltin bromide, a known GST inhibitor. In contrast, the binding of N-acetoxy-IQ or N-acetoxy-MeIQx to DNA was unaffected by addition of the human or rat GSTs; however, GSH alone significantly inhibited (40%) their binding to DNA. High-performance liquid chromatographic analyses of incubation mixtures containing N-acetoxy-PhIP, GSH, and GST A1-1 failed to detect GSH conjugates of PhIP. Only oxidized glutathione and the parent amine, PhIP, were detected as reaction products, suggesting a redox mechanism. GST activity in human hepatic and colon mucosal cytosols was subsequently examined using the synthetic or O-acetyltransferase-generated N-acetoxy derivatives of PhIP, IQ, and MeIQx as substrates. GST activity toward N-acetoxy-PhIP was expressed in all 8 livers but not in 6 colons. No activity toward N-acetoxy-IQ or N-acetoxy-MeIQx was detected in human liver cytosols. This study indicates that a GST-dependent detoxification pathway may be an important determinant for the organ specificity of the heterocyclic amine carcinogens. Moreover, the high specificity of the reaction for GST A1-1, which is known to be inducible by cruciferous and yellow-green vegetable consumption, is consistent with the protective effects of such diets against human colorectal cancer.

Animals↗
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

Photoaffinity labelling of the active site of the rat glutathione transferases 3-3 and 1-1 and human glutathione transferase A1-1.

The glutathione transferases (GSTs) form a group of enzymes responsible for a wide range of molecular detoxications. The photoaffinity label S-(2-nitro-4-azidophenyl)glutathione was used to study the hydrophobic region of the active site of the rat liver GST 1-1 and 2-2 isoenzymes (class Alpha) as well as the rat class-Mu GST 3-3. Photoaffinity labelling was carried out using a version of S-(2-nitro-4-azidophenyl)glutathione tritiated in the arylazido ring. The labelling occurred with higher levels of radioisotope incorporation for the Mu than the Alpha families. Taking rat GST 3-3, 1.18 (+/- 0.05) mol of radiolabel from S-(2-nitro-4-azidophenyl)glutathione was incorporated per mol of dimeric enzyme, which could be blocked by the presence of the strong competitive inhibitor, S-tritylglutathione (Ki = 1.4 x 10(-7) M). Radiolabelling of the protein paralleled the loss of enzyme activity. Photoaffinity labelling by tritiated S-(2-nitro-4-azidophenyl)glutathione on a preparative scale (in the presence and absence of S-tritylglutathione) followed by tryptic digestion and purification of the labelled peptides indicated that GST 3-3 was specifically photolabelled; the labelled peptides were sequenced. Similarly, preparative photoaffinity labelling by S-(2-nitro-4-azidophenyl)glutathione of the rat liver 1-1 isoenzyme, the human GST A1-1 and the human-rat chimaeric GST, H1R1/1, was carried out with subsequent sequencing of radiolabelled h.p.l.c.-purified tryptic peptides. The results were interpreted by means of molecular-graphics analysis to locate photoaffinity-labelled peptides using the X-ray-crystallographic co-ordinates of rat GST 3-3 and human GST A1-1. The molecular-graphical analysis indicated that the labelled peptides are located within the immediate vicinity of the region occupied by S-substituted glutathione derivatives bound in the active-site cavity of the GSTs investigated.

Affinity Labels↗
PubMed1994

Kinetics and equilibria of S-nitrosothiol-thiol exchange between glutathione, cysteine, penicillamines and serum albumin.

The kinetics and equilibria of S-nitrosothiol-thiol (SNO-SH) exchange reactions were determined using differential optical absorption. At pH 7.4 and 37 degrees C, k2 values ranged from 0.9 M-1.s-1 for the reaction between S-nitroso-glutathione (GSNO) and N-acetyl-penicillamine, and up to 279 M-1.s-1 for the exchange between S-nitroso-penicillamine (penSNO) and GSH. SNO-SH exchange involving GSH/GSNO and cysteine/cySNO was relatively rapid, k2 approx. 80 M-1.s-1 with an equilibrium constant slightly in favour of GSNO. GSNO was strongly favoured in equilibrium with penSNO, keq 0.0039. In the case of SNO-SH exchange between S-nitroso human serum albumin (albSNO) and GSH or cysteine k2 values were 3.2 and 9.1 M-1.s-1, respectively. The results show that the initial rate of SNO-SH exchange between physiological albSNO (7 microM) and venous plasma levels of GSH and cysteine is very slow, < 1%/min. On the other hand, if a nitrosothiol such as cySNO were to enter a cell, it would be rapidly converted to GSNO (43%/s).

Cysteine↗
PubMed1994

Human glutathione S-transferase theta (GSTT1): cDNA cloning and the characterization of a genetic polymorphism.

In humans, glutathione-dependent conjugation of halomethanes is polymorphic, with 60% of the population classed as conjugators and 40% as non-conjugators. We report the characterization of the genetic polymorphism causing the phenotypic difference. We have isolated a cDNA that encodes a human class Theta GST (GSTT1) and which shares 82% sequence identity with rat class Theta GST5-5. From PCR and Southern blot analyses, it is shown that the GSTT1 gene is absent from 38% of the population. The presence or absence of the GSTT1 gene is coincident with the conjugator (GSST1+) and non-conjugator (GSTT1-) phenotypes respectively. The GSTT1+ phenotype can catalyse the glutathione conjugation of dichloromethane, a metabolic pathway which has been shown to be mutagenic in Salmonella typhimurium mutagenicity tester strains and is believed to be responsible for carcinogenicity of dichloromethane in the mouse. In humans, the enzyme is found in the erythrocyte and this may act as a detoxification sink. Characterization of the GSTT1 polymorphism will thus enable a more accurate assessment of human health risk from synthetic halomethanes and other industrial chemicals.

Amino Acid Sequence↗
PubMed1994

Theta class glutathione S-transferase GSTT1 genotypes and susceptibility to cervical neoplasia: interactions with GSTM1, CYP2D6 and smoking.

The factors that determine progression of cervical intra-epithelial neoplasia (CIN) to squamous cell carcinoma (SCC) are unknown. Cigarette smoking is a risk factor, suggesting polymorphism at loci that encode carcinogen-metabolizing enzymes such as glutathione S-transferase (GSTT1, GSTM1) and cytochrome P450 (CYP2D6) may determine susceptibility to these cancers. We have studied the frequency of the null genotype at the theta class GSTT1 locus in women with low-grade CIN, high-grade CIN and SCC. The control group comprised women with normal cervical pathology suffering menorrhagia. We found the frequency of GSTT1 null in the control and case groups was not significantly different, though frequency distributions of combinations of the genotype with smoking in mutually exclusive groups in the high-grade CIN group and the other case groups were significantly different. Interactive effects of GSTT1 null with the GSTM1 null and CYP2D6 EM genotypes, and cigarette smoking were also studied by comparing the multinomial frequency distributions of these factors over mutually exclusive categories. These showed no significant differences between the controls and SCC or low-grade CIN. Frequency distributions in high-grade CIN, however, were significantly different to the controls, and both SCC and low-grade CIN; frequency distributions of GSTT1 null with smoking and CYP2D6 EM, individually and in combination, were significantly different. However, inspection of our data does not indicate that GSTT1 null is a major factor mediating risk. Thus, comparison of chi 2 values for the differences between frequency distributions in high-grade CIN and other groups shows that values for combinations of GSTT1 null with other factors are lower than those for equivalent combinations with smoking and CYP2D6 EM. Interestingly, the combination GSTT1 null/GSTM1 null did not appear to influence susceptibility to CIN or SCC.

Adult↗
PubMed1993

Immunohistochemical localization of glutathione S-transferases in human lung.

Glutathione S-transferases (GST) detoxify a number of carcinogenic electrophiles including diol-epoxide metabolites of polycyclic aromatic hydrocarbons. The distribution of GSTs A1/A2, M1, M2, M3, and P1 has been studied in lung tissue from 32 subjects by immunohistochemistry using rabbit polyclonal antibodies. GSTA1/A2 and GSTP1 were found to be the most abundant GSTs in human lung, being present in the bronchial and bronchiolar epithelium of all individuals studied. The staining intensity for GSTA1/A2 varied more than that for GSTP1 between individuals. GSTM1, a polymorphic mu-class enzyme, was ambiguously detected in lung tissue and, if expressed, is present at very low levels. GSTM2, a striated muscle-specific isozyme, occurred minimally in the epithelium of the terminal airways, and GSTM3, an enzyme of broad extrahepatic occurrence, was observable in the ciliated airway epithelium and smooth muscle of the lung. The staining for GSTM3 varied from minimal to very intense between individuals; in the bronchial epithelium, it was more abundant in current smokers than in exsmokers. The immunostaining for GSTs in general was most intense in the bronchial epithelium decreasing in the distal airways, in contrast to the previously described peripheral localization of the polycyclic aromatic hydrocarbons activating the P450IA1 enzyme. The localization of GSTs in the bronchial wall suggests that GST polymorphisms may contribute to susceptibility, especially to bronchial tumors of tobacco smokers.

Adult↗
PubMed1993

Distribution of the monochlorobimane-glutathione conjugate between nucleus and cytosol in isolated hepatocytes.

The nuclear/cytoplasmic distributions of the GSH and N-acetylcysteine conjugates of monochlorobimane (MCB) have been studied in rat hepatocytes in primary culture after microinjection into the cytoplasm. The immediately occurring fluorescence (within 1-2 s) in the nucleus was much greater than that in the cytoplasm. Other water-soluble fluorescent markers such as Cascade Blue, 6-carboxyfluorescein and Lucifer Yellow also exhibited a similar nuclear localization. MCB, which is poorly soluble in water, gave similar results whether exposed to the exterior of the cell or microinjected as a solution in ethanol. It is concluded that the fluorophores studied here diffuse into the nucleus and accumulate there, including MCB-GSH formed intracellularly from MCB and GSH. Therefore MCB may be of limited value in estimating concentrations of GSH in the nucleus and the cytoplasm, as recently suggested by Bellomo, Vairetti, Stivala, Mirabelli, Richelmi and Orrenius [(1992) Proc. Natl. Acad. Sci. U.S.A. 89, 4412-4416].

Cell Nucleus↗
PubMed1993

Expression of mammalian glutathione S-transferase 5-5 in Salmonella typhimurium TA1535 leads to base-pair mutations upon exposure to dihalomethanes.

Dihalomethanes can produce liver tumors in mice but not in rats, and concern exists about the risk of these compounds to humans. Glutathione (GSH) conjugation of dihalomethanes has been considered to be a critical event in the bioactivation process, and risk assessment is based upon this premise; however, there is little experimental support for this view or information about the basis of genotoxicity. A plasmid vector containing rat GSH S-transferase 5-5 was transfected into the Salmonella typhimurium tester strain TA1535, which then produced active enzyme. The transfected bacteria produced base-pair revertants in the presence of ethylene dihalides or dihalomethanes, in the order CH2Br2 > CH2BrCl > CH2Cl2. However, revertants were not seen when cells were exposed to GSH, CH2Br2, and an amount of purified GSH S-transferase 5-5 (20-fold excess in amount of that expressed within the cells). HCHO, which is an end product of the reaction of GSH with dihalomethanes, also did not produce mutations. S-(1-Acetoxymethyl)GSH was prepared as an analog of the putative S-(1-halomethyl)GSH reactive intermediates. This analog did not produce revertants, consistent with the view that activation of dihalomethanes must occur within the bacteria to cause genetic damage, presenting a model to be considered in studies with mammalian cells. S-(1-Acetoxymethyl)GSH reacted with 2'-deoxyguanosine to yield a major adduct, identified as S-[1-(N2-deoxyguanosinyl)methyl]GSH. Demonstration of the activation of dihalomethanes by this mammalian GSH S-transferase theta class enzyme should be of use in evaluating the risk of these chemicals, particularly in light of reports of the polymorphic expression of a similar activity in humans.

Animals↗
PubMed1993

Unusual reactivity of Tyr-7 of GSH transferase P1-1.

Reaction of human GSH transferase P1-1 (GSTP1-1) with diethylpyrocarbonate (DEPC) at pH 7.0 and 4 degrees C resulted in covalent modification of an equivalent of one histidine and one tyrosine residue per subunit, with loss of activity. Sequence analysis showed that His-71 and Tyr-7 were modified. Reference to the three-dimensional structure of GSTP1-1 [Reinemer, Dirr, Ladenstein, Huber, Lo Bello, Frederici and Parker (1992) J. Mol. Biol. 227, 214-226] shows that the modification of Tyr-7 is most likely to affect enzyme activity. Kinetic analysis of the DEPC modification of Tyr-7 in GSTP1-1 gave a k2 approx. 150 times that of a peptide comprising residues 1-11 of GSTP1-1. The reaction of Tyr-7 of GSTP1-1 with DEPC was poorly inhibited by 1 mM GSH (14%) or 10 microM S-hexylglutathione (18%). DEPC treatment of the enzyme altered the absorbance at 290 nm in second-derivative spectra, suggesting that a significant amount of tyrosinate ion occurs in the enzyme. GSH, however, did not significantly alter the A290. The data provide the first evidence of unusual chemical reactivity of Tyr-7 and are consistent with its proposed role as a proton acceptor during catalysis.

Diethyl Pyrocarbonate↗
PubMed1993

Chemical modification of GSH transferase P1-1 confirms the presence of Arg-13, Lys-44 and one carboxylate group in the GSH-binding domain of the active site.

GSH transferase P1-1 (GSTP1-1) was modified with group-specific reagents. Kinetic experiments demonstrated that inactivation of GSTP1-1 occurred upon reaction of one arginine residue per subunit with diacetyl, one lysine residue per subunit with 2,4,6-trinitrobenzene sulphonate, or one carboxylate group per subunit with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide. All three inactivation reactions were inhibited by compounds known to bind at the GSH site of the enzyme but were unaffected by the electrophile 1-chloro-2,4-dinitrobenzene. N-terminal sequence analysis showed that Arg-13 was modified by diacetyl and that this modification was inhibited by GSH. Arg-11 was not modified. The lysine residue modified by 2,4,6-trinitrobenzene sulphonate and protected by S-octylglutathione was identified as Lys-44 by sequencing of tryptic peptides. The findings are in agreement with the involvement of Arg-13 and Lys-44 in binding of GSH, as determined from the crystal structure [Reinemer, Dirr, Ladenstein, Huber, Lo Bello, Frederici and Parker (1992) J. Mol. Biol. 227, 214-226]. The present data also implicate a single carboxylate in GSH binding, consistent with the involvement of Asp-98 of subunit B determined from the crystallographic study. The GSH-binding determinants of GSTP1-1 are compared using sequence similarity with those of GSTs of Alpha, Mu and Theta classes.

Amino Acid Sequence↗
PubMed1993

The human glutathione S-transferase P1-1 gene: modulation of expression by retinoic acid and insulin.

Glutathione S-transferases (GSTs) are a group of enzymes which play an important role in the detoxication of xenobiotics. It is shown that the expression of human glutathione S-transferase P1-1 (GSTP1-1) is suppressed by retinoic acid (RA) as the result of decreased transcription from its gene, GSTP1. Chloramphenicol acetyltransferase (CAT) assays indicate that the effect of RA on the transcription of a GSTP1 promoter-CAT fusion gene is mediated by the region -99 to +72 of GSTP1. A consensus activator protein 1-binding site, located at nucleotide position -59 to -65 of GSTP1, is suggested to be responsible for RA repression. This effect of RA on GSTP1 expression is mediated by the human beta-type RA receptor, hRAR beta, but not the chicken retinoid X receptor, cRXR. The retinoid X receptor does not augment the action of hRAR beta on GSTP1. In addition, it is shown that GSTP1-1 expression is enhanced by insulin as a result of increased transcription of GSTP1. Assay of CAT activity indicates that the effect of insulin on the transcription of GSTP1 is also mediated by the region -99 to +72 of GSTP1. Comparison with sequences of other insulin-responsive genes, suggests that insulin enhancement of GSTP1 expression is effected by an eight-base-pair sequence, 'CCCGCGTC', located at +48 to +55 in intron 1 of the gene. These results are discussed in relation to the increased expression of GSTP1-1 in many tumour cells.

Animals↗
PubMed1993

Constitutive and inducible profile of glutathione S-transferase subunits in biliary epithelial cells and hepatocytes isolated from rat liver.

The constitutive and inducible cytosolic glutathione S-transferase (EC 2.5.1.18) subunit compositions of parenchymal cells (hepatocytes) and biliary epithelial cells (BEC) from rat liver have been quantitatively analysed using reverse-phase h.p.l.c. Hepatocytes, analysed in the absence of non-parenchymal cells, expressed constitutively the following subunits, in order of their concentration: 3, 4, 2, 1a, 1b, 8, 6 and 10. BEC express constitutively only four of the GST subunits expressed by hepatocytes and these are, in order of their concentration: subunits 2, 7, 4 and 3. Notable differences from hepatocytes are that BEC completely lack the Alpha-class subunits 1a and 1b that are major subunits in hepatocytes, Mu-class subunits make up a very low proportion of the total, and the Pi-class subunit 7 is a major subunit in BEC, whereas it is essentially absent from hepatocytes. For the first time, the effects of the inducing agents phenobarbitone (PB), beta-naphthoflavone (beta-NF) and ethoxyquin (EQ) have been characterized in a comprehensive and quantitative manner in both cell types. PB, beta-NF and EQ increased total GST protein in hepatocytes by approx. 2-fold, 3-fold and 4-fold respectively. Subunits significantly induced in hepatocytes were (in order of fold-induction): by PB, 1b > 8 > 3 > 2 > 4; by beta-NF, 1b > 8 > 2 > 3 > 4; and by EQ, 7 > 1b > 10 > 8 > 3 > 2 > 1a > 4. In BEC, neither PB nor beta-NF had significant effects on the total amount of GST protein, although PB did significantly induce subunit 3 at the expense of other subunits. EQ increased total GST protein nearly 5-fold in BEC, subunits 7 and 3 being induced dramatically above constitutive levels.

Animals↗