Purification and characterization of two glutathione S-aryltransferase activities from rat liver.
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ABSTRACT:
SUBMITTER: Askelof P
PROVIDER: S-EPMC1165479 | biostudies-other | 1975 Jun
REPOSITORIES: biostudies-other
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Project description:GSH-dependent enzymic reduction of dehydroascorbic acid to ascorbic acid has been studied in rat liver cytosol. After gel filtration of cytosol on Sephadex G-100 SF, dehydroascorbate reductase activity was recovered in two distinct peaks, one corresponding to glutaredoxin (an enzyme already known for its dehydroascorbate reductase activity) and another, much larger one, corresponding to a novel enzyme different from glutaredoxin. The latter was purified to apparent homogeneity. The purification process involved (NH4)2SO4 fractionation, followed by DEAE-Sepharose, Sephadex G-100 SF and Reactive Red chromatography. SDS/PAGE of the purified enzyme in either the presence or absence of 2-mercaptoethanol demonstrated a single protein band of M(r) 31,000. The M(r) determined by both Sephadex G-100 SF chromatography and h.p.l.c. was found to be approx. 48,000. H.p.l.c. of the denatured enzyme gave an M(r) value identical with that obtained by SDS/PAGE (31,000). The apparent Km for dehydroascorbate was 245 microM and the Vmax. was 1.9 mumol/min per mg of protein; for GSH they were 2.8 mM and 4.5 mumol/min per mg of protein respectively. The optimal pH range was 7.5-8.0. Microsequence analysis of the electro-transferred enzyme band showed that the N-terminus is blocked. Data on internal primary structure were obtained from CNBr-and N-chlorosuccinimide-derived fragments. No significative sequence similarity was found to any of the protein sequences contained in the Protein Identification Resource database.
| S-EPMC1137105 | biostudies-other
Project description: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)
| S-EPMC1152444 | biostudies-other
Project description:DNA peroxidized by exposure to ionizing radiation in the presence of oxygen is a substrate for the Se-independent GSH peroxidase activity of several GSH transferases, GSH transferases 5-5, 3-3 and 4-4 being the most active in the rat liver soluble supernatant fraction (500, 35 and 20 nmol/min per mg of protein respectively) and GSH transferases mu and pi the most active, so far found, in the human liver soluble supernatant fraction (80 and 10 nmol/min per mg respectively). Although the GSH transferase content of the rat nucleus was found to be much lower than that of the soluble supernatant, nuclear GSH transferases are likely to be more important in the detoxification of DNA hydroperoxide produced in vivo. Two nuclear fractions were studied, one extracted with 0.075 M-saline/0.025 M-EDTA, pH 8.0, and the other extracted from the residue with 8.5 M-urea. The saline/EDTA fraction contained subunits 1, 2, 3, 4 and a novel subunit, similar but not identical to 5, provisionally referred to as 5*, in the proportions 40:25:5:5:25 respectively. The 8.5 M-urea-extracted fraction contained principally subunit 5* together with a small amount of subunit 6 in the proportion 95:5 respectively. GSH transferase 5*-5* purified from the 8.5 M-urea extract has the highest activity towards DNA hydroperoxide of any GSH transferase so far studied (1.5 mumol/min per mg). A Se-dependent GSH peroxidase fraction from rat liver was also active towards DNA hydroperoxide; however, since this enzyme accounts for only 14% of the GSH peroxidase activity detectable in the nucleus, GSH transferases may be the more important source of this activity. The possible role of GSH transferases, in particular GSH transferase 5*-5*, in DNA repair is discussed.
| S-EPMC1135159 | biostudies-other
Project description:Objectives:To purify and characterize the glutathione binding protein GsiB of glutathione importer (GSI) in Escherichia coli (E. coli). Results:The coding sequence of GsiB was cloned from E. coli MG1655 and expressed in BL21(DE3). GsiB protein was expressed and purified to homogeneity using Ni-affinity and gel filtration chromatography. SDS-PAGE of purified GsiB showed a single protein band of molecular mass 56 kDa, while native gel showed two bands around 56 kDa and 110 kDa. Gene knockout showed that GsiB was essential for GSI mediated glutathione import. Interactions of GsiA, B, C, and D were determined using bacterial two-hybrid method. Without glutathione, GsiB showed no direct interaction with the other three proteins. However, GsiB could interact with GsiC and GsiD when using glutathione as sole sulfur source. Conclusions:GsiB functions in E. coli was characterized which could help elucidate the glutathione import mechanism in gram-negative bacteria.
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Project description:1. Rat liver glycosylasparaginase [N4-(beta-N-acetylglucosaminyl)-L-asparaginase, EC 3.5.1.26] was purified to homogeneity by using salt fractionation, CM-cellulose and DEAE-cellulose chromatography, gel filtration on Ultrogel AcA-54, concanavalin A-Sepharose affinity chromatography, heat treatment at 70 degrees C and preparative SDS/polyacrylamide-gel electrophoresis. The purified enzyme had a specific activity of 3.8 mumol of N-acetylglucosamine/min per mg with N4-(beta-N-acetylglucosaminyl)-L-asparagine as substrate. 2. The native enzyme had a molecular mass of 49 kDa and was composed of two non-identical subunits joined by strong non-covalent forces and having molecular masses of 24 and 20 kDa as determined by SDS/polyacrylamide-gel electrophoresis. 3. The 20 kDa subunit contained one high-mannose-type oligosaccharide chain, and the 24 kDa subunit had one high-mannose-type and one complex-type oligosaccharide chain. 4. N-Terminal sequence analysis of each subunit revealed a frayed N-terminus of the 24 kDa subunit and an apparent N-glycosylation of Asn-15 in the same subunit. 5. The enzyme exhibited a broad pH maximum above 7. Two major isoelectric forms were found at pH 6.4 and 6.6. 6. Glycosylasparaginase was stable at 75 degrees C and in 5% (w/v) SDS at pH 7.0.
| S-EPMC1138631 | biostudies-other
Project description:The olfactory epithelium is continuously exposed to exogenous chemicals, including odorants. During the past decade, the enzymes surrounding the olfactory receptors have been shown to make an important contribution to the process of olfaction. Mammalian xenobiotic metabolizing enzymes, such as cytochrome P450, esterases and glutathione transferases (GSTs), have been shown to participate in odorant clearance from the olfactory receptor environment, consequently contributing to the maintenance of sensitivity toward odorants. GSTs have previously been shown to be involved in numerous physiological processes, including detoxification, steroid hormone biosynthesis, and amino acid catabolism. These enzymes ensure either the capture or the glutathione conjugation of a large number of ligands. Using a multi-technique approach (proteomic, immunocytochemistry and activity assays), our results indicate that GSTs play an important role in the rat olfactory process. First, proteomic analysis demonstrated the presence of different putative odorant metabolizing enzymes, including different GSTs, in the rat nasal mucus. Second, GST expression was investigated in situ in rat olfactory tissues using immunohistochemical methods. Third, the activity of the main GST (GSTM2) odorant was studied with in vitro experiments. Recombinant GSTM2 was used to screen a set of odorants and characterize the nature of its interaction with the odorants. Our results support a significant role of GSTs in the modulation of odorant availability for receptors in the peripheral olfactory process.
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Project description:The liver plays a major role in the metabolism of plasma high-density lipoprotein (HDL). Several groups have postulated, but others refuted, the existence of a classical membrane receptor which recognizes HDL. In the present study, we identified and purified two liver HDL-binding proteins of 120 kDa (HB1) and 100 kDa (HB2), with apparent specificity for HDL3 devoid of E apolipoprotein. The plasma membrane was the richest source of the HDL-binding protein. Both proteins bound A-I and A-II apolipoproteins and retained HDL-binding activity after final purification. HB1 activity, but not that of HB2, was lost after treatment with beta-mercaptoethanol, but reduction did not change the apparent molecular mass of either protein. Antibodies against HB1 or HB2 did not cross-react, and preliminary structural investigations provide evidence to suggest that HB1 and HB2 are not structurally related. We thus provide evidence for at least two liver plasma-membrane proteins which bind HDL apolipoproteins, suggesting that protein-protein interaction participates to some degree in the mechanism of HDL recognition by cells.
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Project description:Glutathione (GSH) is transported into renal mitochondria by the dicarboxylate (DIC; Slc25a10) and 2-oxoglutarate carriers (OGC; Slc25a11). To determine whether these carriers function similarly in liver mitochondria, we assessed the effect of competition with specific substrates or inhibitors on GSH uptake in isolated rat liver mitochondria. GSH uptake was uniphasic, independent of ATP hydrolysis, and exhibited K(m) and V(max) values of 4.08 mM and 3.06 nmol/min per mg protein, respectively. Incubation with butylmalonate and phenylsuccinate inhibited GSH uptake by 45-50%, although the individual inhibitors had no effect, suggesting in rat liver mitochondria, the DIC and OGC are only partially responsible for GSH uptake. H4IIE cells, a rat hepatoma cell line, were stably transfected with the cDNA for the OGC, and exhibited increased uptake of GSH and 2-oxoglutarate and were protected from cytotoxicity induced by H(2)O(2), methyl vinyl ketone, or cisplatin, demonstrating the protective function of increased mitochondrial GSH transport in the liver.
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Project description:Minoxidil (Mx), a pyrimidine N-oxide, is used therapeutically as an antihypertensive agent and to induce hair growth in patients with male pattern baldness. Mx NO-sulphate has been implicated as the agent active in producing these effects. This paper describes the purification of a unique sulphotransferase (ST) from rat liver cytosol that is capable of catalysing the sulphation of Mx. By using DEAE-Sepharose CL-6B chromatography, hydroxyapatite chromatography and ATP-agarose affinity chromatography, Mx-ST activity was purified 240-fold compared with the activity in cytosol. The purified enzyme was also capable of sulphating p-nitrophenol (PNP) at low concentrations (less than 10 microM). Mx-ST was purified to homogeneity, as evaluated by SDS/PAGE and reverse-phase h.p.l.c. The active form of the enzyme had a molecular mass of 66,000-68,000 Da as estimated by gel exclusion chromatography and a subunit molecular mass of 35,000 Da. The apparent Km values for Mx, 3'-phosphoadenosine 5'-phosphosulphate and PNP were 625 microM, 5.0 microM and 0.5 microM respectively. However, PNP displayed potent substrate inhibition at concentrations above 1.2 microM. Antibodies raised in rabbits to the pure enzyme detected a single band in rat liver cytosol with a subunit molecular mass of 35,000 Da, as determined by immunoblotting. The anti-(rat Mx-ST) antibodies also reacted with the phenol-sulphating form of human liver phenol sulphotransferase, suggesting some structural similarity between these proteins.
| S-EPMC1131791 | biostudies-other
Project description:Oral administration of glutathione has been demonstrated to reduce exercise-induced fatigue and improve liver function, although glutathione can be synthesized in the liver. However, little is known about the underlying mechanism of this effect. To address this, the status of food-derived glutathione in the intestine, blood, and liver was examined. Glutathione-1-13C or N-acetyl-cysteine-1-13C (NAC) was orally administered to rats (50 mg/kg). Food-derived glutathione contents within tissues were estimated by subtracting endogenous glutathione-1-13C from the total glutathione-1-13C. Food-derived glutathione was present in rat intestines and livers (approximately 60 and 300 μmol/kg, respectively, 120 min after ingestion) in electrochemically reduced form, while all food-derived glutathione in the blood plasma was conjugated with proteins and low-molecular-weight thiol compounds. However, no significant amounts of NAC-derived glutathione were detected in the blood plasma. These findings indicate that food-derived glutathione is directly absorbed in its electrochemically reduced form in the intestine, is then transported in the blood in bound forms, and is finally deposited into the liver in reduced form. Therefore, upon entering the bloodstream, food-derived glutathione binds to thiol compounds and releases hydrogen atom; subsequently, it does the reverse upon incorporation into the liver, which might impact the physiological redox condition. With respect to food-derived glutathione and cysteine-containing peptides, this study provides new insights on their modes of transportation and mechanisms of action.
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