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PubMed1985

Changes in carnitine-palmitoyl-transferase and carnitine-acetyl-transferase activity in rat kidney during development; effects of fasting.

Developmental changes in the activities of two enzymes catalysing transfer of fatty acid across the mitochondrial membrane (carnitine-palmitoyl-transferase and carnitine-acetyl-transferase) were studied in the kidneys of developing rats from late fetal life to 10 days post-partum and were compared to cortical adult value. The activities of carnitine-palmitoyl-transferase and carnitine-acetyl-transferase increased after birth to reach a maximal value on day 5. Thereafter both activities decreased to reach adult cortical value. The cytochrome c oxidase activity (index of mitochondrial activity) increases continuously from late fetal age to adult. In kidneys of fetuses from starved mothers the carnitine-palmitoyl-transferase activity is higher than that of controls while carnitine-acetyl-transferase activity is not changed. In postmature fetuses (23 days post-coïtum) carnitine-palmitoyl-transferase activity is the same as in 21 days post-coïtum old fetuses. These results are discussed in relation to variations in nutritional and hormonal changes occurring during the perinatal period.

Acetyltransferases↗
PubMed1993

Characterization of recombinant human farnesyl-protein transferase: cloning, expression, farnesyl diphosphate binding, and functional homology with yeast prenyl-protein transferases.

We have isolated cDNAs encoding the alpha and beta subunits of human farnesyl-protein transferase (FPTase). The proteins encoded by these two cDNAs are 93-95% identical to the corresponding subunits of bovine and rat FPTase and show regions of homology with proteins encoded by Saccharomyces cerevisiae prenyl-protein transferase genes. Human FPTase expressed in Escherichia coli from a translationally coupled operon had kinetic properties similar to those of FPTase isolated from bovine brain. Examination of farnesyl diphosphate binding indicated that while neither individual subunit was capable of isoprenoid binding, a radiolabeled farnesyl diphosphate analog could be specifically photo-cross-linked to the beta subunit of FPTase holoenzyme. To further analyze subunit structure-function and to detect functional similarities with yeast prenyl-protein transferases (FPTase and two geranylgeranyl-protein transferases), amino acid changes homologous to those found in mutant yeast prenyl-protein transferase subunits were made in the subunits of human FPTase. Substitutions in either the alpha or beta subunits that decrease the activity of yeast prenyl-protein transferases were also observed to impair human FPTase. Kinetic analyses showed that these mutant human FPTases have Km and kcat values that are altered with respect to wild-type human FPTase.

Alkyl and Aryl Transferases↗
PubMed1996

Three-dimensional structure of glutathione S-transferase from Arabidopsis thaliana at 2.2 A resolution: structural characterization of herbicide-conjugating plant glutathione S-transferases and a novel active site architecture.

Glutathione S-transferases (GST) are a family of multifunctional enzymes involved in the metabolization of a broad variety of xenobiotics and reactive endogenous compounds. The interest in plant glutathione S-transferases may be attributed to their agronomic value, since it has been demonstrated that glutathione conjugation for a variety of herbicides is the major resistance and selectivity factor in plants. The three-dimensional structure of glutathione S-transferase from the plant Arabidopsis thaliana has been solved by multiple isomorphous replacement and multiwavelength anomalous dispersion techniques at 3 A resolution and refined to a final crystallographic R-factor of 17.5% using data from 8 to 2.2 A resolution. The enzyme forms a dimer of two identical subunits each consisting of 211 residues. Each subunit is characterized by the GST-typical modular structure with two spatially distinct domains. Domain I consists of a central four-stranded beta-sheet flanked on one side by two alpha-helices and on the other side by an irregular segment containing three short 3(10)-helices, while domain II is entirely helical. The dimeric molecule is globular with a prominent large cavity formed between the two subunits. The active site is located in a cleft situated between domains I and II and each subunit binds two molecules of a competitive inhibitor S-hexylglutathione. Both hexyl moieties are oriented parallel and fill the H-subsite of the enzyme's active site. The glutathione peptide of one inhibitor, termed productive binding, occupies the G-subsite with multiple interactions similar to those observed for other glutathione S-transferases, while the glutathione backbone of the second inhibitor, termed unproductive binding, exhibits only weak interactions mediated by two polar contacts. A most striking difference from the mammalian glutathione S-transferases, which share a conserved catalytic tyrosine residue, is the lack of this tyrosine in the active site of the plant glutathione S-transferase.

Amino Acid Sequence↗
PubMed1988

Dog liver glutathione S-transferase and its strong immunoreactivity with rat transferase-P(7-7).

Dog liver cytosolic glutathione S-transferases (GSTs) were investigated to characterize their properties in comparison with rat liver transferases. Dog liver GSTs after the glutathione affinity column chromatography showed three subunit bands on SDS-polyacrylamide gel electrophoresis. These three subunits, designated as Yd1 (mol.wt 26,000), Yd2 (mol.wt 27,000) and Yd3 (mol.wt 28,000), were distinctly different from rat liver GST subunits, i.e. Ya(1) (mol.wt 26,500), Yb1(3)/Yb2(4) (mol.wt 27,500) and Yc(2) (mol.wt 28,500). Western blot analysis revealed that Yd1, Yd2 and Yd3 were immunoreacted with anti-rat GST 7-7, 1-1 and 3-3 antibodies, respectively. Four transferase activity fractions, I (pH greater than 7.63), II (pH 6.92), III (pH 5.80) and IV (pH 5.65), were obtained from affinity purified GSTs by chromatofocusing. Each fraction exhibited a characteristic substrate specificity. GST-II, III and IV were all strongly immunoreacted with anti-rat GST 7-7 antibody by immunoblotting, thus suggesting the occurrence of the heterogeneity of transferases immunologically related to rat GST subunit 7 in dog liver. Immunohistochemical examination showed that transferases immunoreacted with anti-GST 7-7 antibody have diffusely distributed throughout the lobule, while enzymes related to subunit 3 have been localized in a narrow range of cells around the central vein. These data suggest that GSTs immunologically associated with rat transferase subunit 7 may be major forms in dog liver.

Animals↗
PubMed1986

Purification and physical characterization of glutathione S-transferase K. Differential use of S-hexylglutathione and glutathione affinity matrices to isolate a novel glutathione S-transferase from rat liver.

A novel hepatic enzyme, glutathione S-transferase K, is described that, unlike previously characterized transferases, possesses little affinity for S-hexylglutathione-Sepharose 6B but can be isolated because it binds to a glutathione affinity matrix. A purification scheme for this new enzyme was devised, with the use of DEAE-cellulose, S-hexylglutathione-Sepharose 6B, glutathione-Sepharose 6B and hydroxyapatite chromatography. The final hydroxyapatite step results in the elution of three chromatographically interconvertible forms, K1, K2 and K3. The purified protein has an isoelectric point of 6.1 and comprises subunits that are designated Yk (Mr 25,000); during sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, it migrates marginally faster than the Ya subunit but slower than the pulmonary Yf monomer (Mr 24,500). Transferase K displays catalytic, immunochemical and physical properties that are distinct from those of other liver transferases. Tryptic peptide maps suggest that transferase K is a homodimer, or comprises closely homologous subunits. The tryptic fingerprints also demonstrate that, although transferase K is structurally separate from previously described hepatic forms, a limited sequence homology exists between the Yk, Ya and Yc polypeptides. These structural data are in accord with the immunochemical results presented in the accompanying paper [Hayes & Mantle (1986) Biochem. J. 233, 779-788].

Amino Acids↗
PubMed1997

Cloning and characterization of Helicobacter pylori succinyl CoA:acetoacetate CoA-transferase, a novel prokaryotic member of the CoA-transferase family.

Sequencing of a fragment of Helicobacter pylori genome led to the identification of two open reading frames showing striking homology with Coenzyme A (CoA) transferases, enzymes catalyzing the reversible transfer of CoA from one carboxylic acid to another. The genes were present in all H. pylori strains tested by polymerase chain reaction or slot blotting but not in Campylobacter jejuni. Genes for the putative A and B subunits of H. pylori CoA-transferase were introduced into the bacterial expression vector pKK223-3 and expressed in Escherichia coli JM105 cells. Amino acid sequence comparisons, combined with measurements of enzyme activities using different CoA donors and acceptors, identified the H. pylori CoA-transferase as a succinyl CoA:acetoacetate CoA-transferase. This activity was consistently observed in different H. pylori strains. Antibodies raised against either recombinant A or B subunits recognized two distinct subunits of Mr approximately 26,000 and 24, 000 that are both necessary for H. pylori CoA-transferase function. The lack of alpha-ketoglutarate dehydrogenase and of succinyl CoA synthetase activities indicates that the generation of succinyl CoA is not mediated by the tricarboxylic acid cycle in H. pylori. We postulate the existence of an alternative pathway where the CoA-transferase is essential for energy metabolism.

Acyl Coenzyme A↗
PubMed1983

Isoelectric focusing of glutathione S-transferases: comparison of the acidic transferases from human liver, kidney, lung, spleen and placenta.

The glutathione S-transferase composition of human liver, kidney, lung, spleen and placenta was studied by density gradient isoelectric focusing. On the basis of the enzyme distribution it was possible to divide the supernatants into two groups: one having a predominance of basic activity, the other acidic. Each supernatant consisted of more than one transferase. Human liver and kidney, two major detoxifying organs in the body, bore a clear predominance of basic enzymes and they had the highest transferase activities. The activity of the other organs consisted of almost only a single acidic transferase. Properties of the major acidic transferases from the organs were compared. Prior to the studies the enzymes underwent partial two-step purification. According to the comparison it seems evident that the major acidic transferases from human kidney, lung, spleen and placenta are either closely related or identical.

Female↗
PubMed1988

Acidic and basic forms of glutathione S-transferases from human placenta and comparison with human kidney glutathione S-transferase.

Glutathione S-transferase (GSH-transferase) was purified from human placenta and kidney by affinity chromatography on S-glutathione-carbamidomethyl-epsilon-aminolysyl-Sepharose CL 4B and gel filtration chromatography on Sephades G-75. Electrophoretically pure enzyme with the specific activities of 50.7 and 55.9 U/mg, respectively, were obtained. In addition to the known acidic isoenzyme from human placenta (isoelectric point, pI, 4.5), we describe here for the first time the presence of 6 basic forms with pI values between 8.0 and 9.0. The kidney GSH-transferase contained 2 acidic forms with isoelectric points at 4.6 and 4.65, and 6 basic forms with pI values between 8.7 and 9.4. The basic and acidic isoenzymes from placenta were separated by ion exchange chromatography on Sephadex DEAE A-25. The acidic form accounted for 36% of the total GSH-transferase activity from placenta. Antibodies against the kidney enzyme were raised in rabbit. Total cross-reactivity of placental GSH-transferase with antikidney-GSH-transferase antibodies was obtained, suggesting that the kidney and placental enzymes are immunologically closely related.

Adult↗
PubMed1991

Isolation of a functional transferase component from the rat fatty acid synthase by limited trypsinization of the subunit monomer. Formation of a stable functional complex between transferase and acyl carrier protein domains.

Limited trypsinization of rat fatty acid synthase monomers results in cleavage at sites protected in the native dimer. A 47,000-Da polypeptide containing the transferase component was isolated from the digest and its location in the multifunctional polypeptide established. Both acetyl and malonyl moieties are transferred stoichiometrically from CoA ester to this polypeptide and each can replace the other, confirming that a single common site is utilized in the loading of these substrates onto the fatty acid synthase. Transferase activity of the 47,000-Da polypeptide decreases with increasing acyl donor chain length (malonyl = acetyl greater than butyryl greater than hexanoyl greater than octanoyl). Activity is inhibited by certain thiol-directed reagents, and protection is afforded by substrate suggesting the presence of a sensitive cysteine residue near the substrate binding site. The transferase was also able to utilize as acyl acceptor the Escherichia coli acyl carrier protein and the acyl carrier protein domain of the multifunctional fatty acid synthase. When the fatty acid synthase monomer was trypsinized under milder conditions, the 47,000-Da transferase domain could be isolated in association with the 8,000-Da acyl carrier protein domain. The transferase was capable of translocating substrate moieties from CoA ester donors to the associated acyl carrier protein. The results provide the first direct evidence that, in the head-to-tail oriented fatty acid synthase homodimer, functional communication between the transferase domain located near the end of one polypeptide and the acyl carrier protein domain located at the opposite end of the other polypeptide is facilitated by a stable physical interaction between these domains.

Acyl Carrier Protein↗
PubMed1982

Microsomal glutathione S-transferase. Purification, initial characterization and demonstration that it is not identical to the cytosolic glutathione S-transferases A, B and C.

Rat liver microsomal glutathione S-transferase was activated with N-ethylmaleimide, solubilized with Triton X-100, and purified by chromatography on hydroxyapatite and CM-Sepharose. A 36-fold purification resulted in a 36% yield, indicating that the glutathione S-transferase accounts for 2.5-3% of the original microsomal protein. The purified protein moved as a band with an apparent molecular weight of 14 000 on sodium dodecyl sulphate gel electrophoresis and appeared to be nearly homogeneous. The complex formed between the purified microsomal glutathione S-transferase and Triton X-100 has a sedimentation coefficient of 3.2 S, a partial specific volume of 0.844 cm3/g, and a Stokes radius of 5.5 nm. The complex has a molecular weight of 127 000 and contains three or four polypeptide chains and 112-134 detergent molecules. Antibodies directed against soluble glutathione S-transferases A, B and C do not react with the purified microsomal enzyme. This finding, together with differences in molecular weight and substrate specificity, demonstrate that the microsomal glutathione S-transferase is an enzyme distinct from the cytosolic glutathione S-transferases.

Animals↗
PubMed1995

In the biosynthesis of N-glycans in connective tissue of the snail Lymnaea stagnalis of incorporation GlcNAc by beta 2GlcNAc-transferase I is an essential prerequisite for the action of beta 2GlcNAc-transferase II and beta 2Xyl-transferase.

Using a series of relevant substrates, connective tissue of the snail Lymnaea stagnalis was shown to contain beta 1-2 xylosyltransferase (beta 2Xyl-T), beta 1-2 N-acetylglucosaminyltransferase I (beta 2GlcNAc-T I), and beta 1-2 N-acetylglucosaminyltransferase II (beta 2GlcNAc-T II) activities. These enzymes are probably involved in the biosynthesis of the N-linked carbohydrate chains, like those present in hemocyanin. The products formed by incubation of GlcNAc beta 1-2Man alpha 1-6(GlcNAc beta 1-2Man alpha 1-3)Man beta 1-R [where R = -4GlcNAc beta 1-4GlcNAc or O-(CH2)7CH3] with UDP-Xyl and connective tissue microsomes have been purified and characterized by 1H-NMR spectroscopy in conjunction with methylation analysis to be GlcNAc beta 1-2Man alpha 1-6(GlcNAc beta 1-2Man alpha 1-3)(Xyl beta 1-2)Man beta 1-R. Substrate specificity studies focused on connective tissue beta 2Xyl-T show that the minimal structure requirements are fulfilled in GlcNAc beta 1-2Man alpha 1-3Man beta 1-O-(CH2)7CH3. The enzyme activity can therefore be characterized as UDP-Xyl:Glc-NAc beta 1-2Man alpha 1-3Man beta-R (Xyl to Man beta) beta 1-2 xylosyltransferase. In substrate-specificity studies directed to connective tissue beta 2GlcNAc-T I, it could be demonstrated that the enzyme is active towards acceptors having at the minimum a Man alpha 1-3Man beta-R sequence, and that introduction of a beta Xyl residue at C2 of beta Man totally abolishes the enzyme activity. Xylose-containing oligosaccharides are not acceptors for beta 2GlcNAc-T I. In combination with the substrate specificity of beta Xyl-T, this shows that in snail connective tissue beta 2GlcNAc-T I must act before beta 2Xyl-T. The connective tissue beta 2GlcNAc-T II activity follows the earlier established biosynthetic routes. Based on the substrate specificities of the various connective tissue glycosyltransferases known so far, and the structures isolated from L. stagnalis hemocyanin, a partial biosynthetic scheme for N-glycosylation in snail connective tissue is proposed.

Animals↗
PubMed1986

A comparison of the reversibility of phosphoethanolamine transferase and phosphocholine transferase in rat brain microsomes.

The reversibility of phosphoethanolamine transferase (EC 2.7.8.1) in rat brain is demonstrated in this paper. Microsomal ethanolamine glycerophospholipids were prelabeled with an intracerebral injection of [3H]ethanolamine 4 h before killing young rats. Labeled CDPethanolamine was produced by incubation of the microsomes with CMP, although to a lesser extent than for the previously observed release of CDPcholine. Ethanolamine and choline glycerophospholipids were labeled with [2-3H]glycerol by incubation with primary cultures of rat brain. Microsomes from rat brains, with diisopropyl phosphofluoridate for inhibition of lipases, were incubated with the labeled glycerophospholipids separately, and labeled diacylglycerols were produced. The kinetic parameters of phosphoethanolamine transferase and phosphocholine transferase (EC 2.7.8.2) were compared by incubating rat brain microsomes with [3H]CMP. Inclusion of AMP in the reaction mixture was necessary in order to inhibit the hydrolysis of CMP by an enzyme with the properties of 5'-nucleotidase (EC 3.1.3.5). For phosphoethanolamine transferase and phosphocholine transferase respectively, the Km values for CMP were 40 and 125 microM and the V values were 2.3 and 21.6 nmol/h per mg protein. The reversibility of both enzymes permits the interconversion of the diacylglycerol moieties of choline and ethanolamine glycerophospholipids. During brain ischemia, a principal pathway for degradation of ethanolamine glycerophospholipids may be by reversal of phosphoethanolamine transferase followed by hydrolysis of diacylglycerols by the lipase.

5'-Nucleotidase↗
PubMed1997

Glutaconate CoA-transferase from Acidaminococcus fermentans: the crystal structure reveals homology with other CoA-transferases.

BACKGROUND: Coenzyme A-transferases are a family of enzymes with a diverse substrate specificity and subunit composition. Members of this group of enzymes are found in anaerobic fermenting bacteria, aerobic bacteria and in the mitochondria of humans and other mammals, but so far none have been crystallized. A defect in the human gene encoding succinyl-CoA: 3-oxoacid CoA-transferase causes a metabolic disease which leads to severe ketoacidosis, thus reflecting the importance of this family of enzymes. All CoA-transferases share a common mechanism in which the CoA moiety is transferred from a donor (e.g. acetyl CoA) to an acceptor, (R)-2-hydroxyglutarate, whereby acetate is formed. The transfer has been described by a ping-pong mechanism in which CoA is bound to the active-site residue of the enzyme as a covalent thiol ester intermediate. We describe here the crystal structure of glutaconate CoA-transferase (GCT) from the strictly anaerobic bacterium Acidaminococcus fermentans. This enzyme activates (R)-2-hydroxyglutarate to (R)-2-hydroxyglutaryl-CoA in the pathway of glutamate fermentation. We initiated this project to gain further insight into the function of this enzyme and the structural basis for the characteristics of CoA-transferases. RESULTS: The crystal structure of GCT was solved by multiple isomorphous replacement to 2.55 A resolution. The enzyme is a heterooctamer and its overall arrangement of subunits can be regarded as an (AB)4tetramer obeying 222 symmetry. Both subunits A and B belong to the open alpha/beta-protein class and can be described as a four-layered alpha/alpha/beta/alpha type with a novel composition and connectivity of the secondary structure elements. The core of subunit A consists of seven alpha/beta repeats resulting in an all parallel central beta sheet, against which helices pack from both sides. In contrast, the centre of subunit B is formed by a ninefold mixed beta sheet. In both subunits the helical C terminus is folded back onto the N-terminal domain to form the third layer of helices. CONCLUSIONS: The active site of GCT is located at the interface of subunits A and B and is formed by loops of both subunits. The funnel-shaped opening to the active site has a depth and diameter of about 20 A with the catalytic residue, Glu54 of subunit B, at the bottom. The active-site glutamate residue is stabilized by hydrogen bonds. Despite very low amino acid sequence similarity, subunits A and B reveal a similar overall fold. Large parts of their structures can be spatially superimposed, suggesting that both subunits have evolved from a common ancestor.

Amino Acid Sequence↗
PubMed2006

Saccharomyces cerevisiae cells have three Omega class glutathione S-transferases acting as 1-Cys thiol transferases.

The Saccharomyces cerevisiae genome encodes three proteins that display similarities with human GSTOs (Omega class glutathione S-transferases) hGSTO1-1 and hGSTO2-2. The three yeast proteins have been named Gto1, Gto2 and Gto3, and their purified recombinant forms are active as thiol transferases (glutaredoxins) against HED (beta-hydroxyethyl disulphide), as dehydroascorbate reductases and as dimethylarsinic acid reductases, while they are not active against the standard GST substrate CDNB (1-chloro-2,4-dinitrobenzene). Their glutaredoxin activity is also detectable in yeast cell extracts. The enzyme activity characteristics of the Gto proteins contrast with those of another yeast GST, Gtt1. The latter is active against CDNB and also displays glutathione peroxidase activity against organic hydroperoxides such as cumene hydroperoxide, but is not active as a thiol transferase. Analysis of point mutants derived from wild-type Gto2 indicates that, among the three cysteine residues of the molecule, only the residue at position 46 is required for the glutaredoxin activity. This indicates that the thiol transferase acts through a monothiol mechanism. Replacing the active site of the yeast monothiol glutaredoxin Grx5 with the proposed Gto2 active site containing Cys46 allows Grx5 to retain some activity against HED. Therefore the residues adjacent to the respective active cysteine residues in Gto2 and Grx5 are important determinants for the thiol transferase activity against small disulphide-containing molecules.

Amino Acid Sequence↗
PubMed1989

Glutathione transferases in rat hepatoma cells. Effects of ascites cells on the isoenzyme pattern in liver and induction of glutathione transferases in the tumour cells.

Rat hepatoma cells grown intraperitoneally as an ascites tumour were analysed with respect to their contents of cytosolic glutathione transferases. In contrast with normal liver tissue, the hepatoma cells were dominated by the class Pi glutathione transferase 7-7. All the major hepatic enzyme forms were down-regulated to almost undetectable concentrations. Livers of rats bearing ascites-hepatoma cells expressed low, but significant, amounts of protein which, by electrophoretic and immunochemical properties, appeared identical with transferase 7-7. This enzyme is not detectable in normal hepatocytes. Treatment of rats with trans-stilbene oxide induced the expression of transferase 7-7 in the livers of normal rats as well as in hepatoma-cell-bearing animals. In addition, a 2-fold induction of transferase 7-7 was measured in the hepatoma ascites cells. No significant elevation of any other enzyme forms in the hepatoma cells was noted.

Animals↗
PubMed1975

Drug conjugation in Gunn rats: reduced UDP-glucuronosyl transferase and UDP-glucosyl transferase activities with increased glycine-N-acyltransferase activity.

Glucuronyl, glucosyl, glutathione, glycine conjugations and epoxide hydration were studied in livers of Wistar and Gunn rats. The activities of bilirubin UDP-glucuronosyl transferase and UDP-glucosyl transferase were reduced in microsomes of homozygous and heterozygous Gunn rats compared to Wistar rats (over 90 and 55-65%, respectively). Conjugation of 4-methylumbelliferone by UDP-glucuronosyl transferase was also reduced (30-35%) in Gunn rats. Treatment of microsomes in vitro with membrane perturbating agents increased the measurable activities but did not change the activity relationships between Wistar and Gunn rats. Microsomal epoxide hydrase and soluble glutathione-S-epoxide transferase activities occurred in Gunn rats at the Wistar level, but mitochondrial glycine-N-acyltransferase activity was elevated in homozygous and heterozygous Gunn rats (66 and 47%, respectively). The reciprocal velocity plots of UDP-glucuronosyl transferase activity were similarly concave in Gunn and Wistar rats.

Acyltransferases↗
PubMed1990

Subcellular distribution of N-ethylmaleimide-stimulatable glutathione S-transferase activity in rat liver. Evidence of localization of glutathione S-transferase in peroxisomal membrane.

Subcellular distribution of glutathione S-transferase activity was investigated as stimulated form by N-ethylmaleimide in rat liver. The stimulated glutathione S-transferase activity was localized in mitochondrial and lysosomal fractions besides microsomes. Among N-ethylmaleimide-treated submitochondrial fractions, glutathione S-transferase activity was stimulated only in outer mitochondrial membrane fraction. In lysosomal fraction, it was suggested that glutathione S-transferase activity in peroxisomes, which is immunochemically related to microsomal transferase, was also stimulated, but not in lysosomes.

Animals↗
PubMed1984

Rat liver glutathione S-transferases. Complete nucleotide sequence of a glutathione S-transferase mRNA and the regulation of the Ya, Yb, and Yc mRNAs by 3-methylcholanthrene and phenobarbital.

With the use of cDNA probes reverse transcribed from purified glutathione S-transferase mRNA templates, four cDNA clones complementary to transferase mRNAs have been identified and characterized. Two clones, pGTB38 and pGTB34, have cDNA inserts of approximately 950 and 900 base pairs, respectively, and hybridize to a mRNA(s) whose size is approximately 980 nucleotides. In hybrid-select translation experiments, pGTB38 and pGTB34 select mRNAs specific for the Ya and Yc subunits of rat liver glutathione S-transferases. Clone pGTB33, which harbors a truncated cDNA insert, hybrid-selects only the Ya mRNA. All of the clones, pGTB38, pGTB34, and pGTB33, hybrid-select another mRNA which is specific for a polypeptide with an electrophoretic mobility slightly greater than the Ya subunit. The entire nucleotide sequence of the full length clone, pGTB38, has been determined and the complete amino acid sequence of the corresponding polypeptide has been deduced. The mRNA codes for a protein comprising 222 amino acids with Mr = 25,547. We have also identified a cDNA clone complementary to a Yb mRNA of the rat liver glutathione S-transferases. This clone, pGTA/C36, hybrid-selects only Yb mRNA(s) and hybridizes to a mRNA(s) whose size is approximately 1200 nucleotides. Although the Ya, Yb, and Yc mRNAs are elevated coordinately by phenobarbital and 3-methylcholanthrene, the Ya-Yc mRNAs are induced to a much greater extent compared to the Yb mRNA(s). These data suggest that the mRNAs for each transferase isozyme are regulated independently.

Amino Acid Sequence↗