Horse-liver glutathione reductase: purification and characterization

Specific Seminal Plasma Fractions Are Responsible for the Modulation of Sperm-PMN Binding in the Donkey

While artificial insemination (AI) with frozen-thawed sperm results in low fertility rates in donkeys, the addition of seminal plasma, removed during cryopreservation, partially counteracts that reduction. Related to this, an apparent inflammatory reaction in jennies is induced following AI with frozen-thawed sperm, as a high amount of polymorphonuclear neutrophils (PMN) are observed within the donkey uterus six hours after AI. While PMN appear to select the sperm that ultimately reach the oviduct, two mechanisms, phagocytosis and NETosis, have been purported to be involved in that clearance. Remarkably, sperm interacts with PMN, but the presence of seminal plasma reduces that binding. As seminal plasma is a complex fluid made up of different molecules, including proteins, this study aimed to evaluate how different seminal plasma fractions, separated by molecular weight (<3, 3-10, 10-30, 30-50, 50-100, and >100 kDa), affect sperm-PMN binding. Sperm motility, viability, and sperm-PMN binding were evaluated after 0 h, 1 h, 2 h, 3 h, and 4 h of co-incubation at 38 °C. Two seminal plasma fractions, including 30-50 kDa or 50-100 kDa proteins, showed the highest sperm motility and viability. As viability of sperm not bound to PMN after 3 h of incubation was the highest in the presence of 30-50 and 50-100 kDa proteins, we suggest that both fractions are involved in the control of the jenny's post-breeding inflammatory response. In conclusion, this study has shown for the first time that specific fractions rather than the entire seminal plasma modulate sperm-PMN binding within the donkey uterus. As several proteins suggested to be involved in the control of post-AI endometritis have a molecular weight between 30 and 100 kDa, further studies aimed at determining the identity of these molecules and evaluating their potential effect in vivo are much warranted.

Moringa Oleifera Leaf Extract Repairs the Oxidative Misbalance following Sub-Chronic Exposure to Sodium Fluoride in Nile Tilapia Oreochromis niloticus

The potential antioxidant property of Moringa oleifera (MO) has been the recent focus of an increased number of studies. However few studies investigated its antioxidative ability against sodium fluoride-induced redox balance breakdown in Oreochromis niloticus. Thus, this study evaluates the effects of MO against the oxidative stress induced by sub-chronic exposure to sodium fluoride (NaF). A total of 264 fish (40 ± 3 g BW) were used to calculate the 96 hr-LC50 of NaF and perform the sub-chronic exposure study. 96 hr-LC50 of NaF was calculated as (61 mg/L). The 1/10 dose of the calculated 96 hr-LC50 (6.1 mg/L) was used to complete the sub chronic exposure for eight weeks. Fish were divided into four groups (n = 51; three replicates each); control, non-treated group; NaF group (exposed to NaF 6.1 mg/L); MO group (treated with 1% MO of diet); and NaF+MO (exposed to NaF 6.1 mg/L and treated with 1% MO of diet). The results revealed that the sub-chronic exposure to NaF (6.1 mg/L) was substantially increased malondialdehyde (MDA) and decrease the activities of superoxide dismutase (SOD), catalase (CAT), glutathione reduced (GSH), glutathione peroxidase (GPx), and total antioxidant capacity (TAC) in the gills, liver, kidney, and muscle tissue in a time-dependent manner. In addition, a significant reduction in mRNA expression of GST in the liver was reported following NaF exposure. On the contrary, dietary supplementation of MO to NaF-exposed fish resulted in a significant reduction in MDA levels, and a significant elevation of SOD, CAT, GSH, GPx, and TAC activities in a time-dependent manner, in addition to significant elevation of GST mRNA expression in liver tissue. It could be concluded that a 1% MO (w/w) ration is a promising antioxidant plant that may successfully use to interfere with the oxidation processes induced by NaF in various tissues of Oreochromis niloticus.

Characterization of recombinant glutathione reductase from the psychrophilic Antarctic bacterium Colwellia psychrerythraea

Glutathione reductases catalyze the reduction of oxidized glutathione (glutathione disulfide, GSSG) using NADPH as the substrate to produce reduced glutathione (GSH), which is an important antioxidant molecule that helps maintain the proper reducing environment of the cell. A recombinant form of glutathione reductase from Colwellia psychrerythraea, a marine psychrophilic bacterium, has been biochemically characterized to determine its molecular and enzymatic properties. C. psychrerythraea glutathione reductase was shown to be a homodimer with a molecular weight of 48.7 kDa using SDS-PAGE, MALDI-TOF mass spectrometry and gel filtration. The C. psychrerythraea glutathione reductase sequence shows significant homology to that of Escherichia coli glutathione reductase (66 % identity), and it possesses the FAD and NADPH binding motifs, as well as absorption spectrum features which are characteristic of flavoenzymes such as glutathione reductase. The psychrophilic C. psychrerythraea glutathione reductase exhibits higher k cat and k cat/K m at lower temperatures (4 °C) compared to mesophilic Baker's yeast glutathione reductase. However, C. psychrerythraea glutathione reductase was able to complement an E. coli glutathione reductase deletion strain in oxidative stress growth assays, demonstrating the functionality of C. psychrerythraea glutathione reductase over a broad temperature range, which suggests its potential utility as an antioxidant enzyme in heterologous systems.

Identification of GR and TrxR systems in Setaria cervi: Purification and characterization of glutathione reductase

The glutathione reductase (GR) and thioredoxin reductase (TrxR) are important enzymes of the redox system that aid parasites to maintain an adequate intracellular redox environment. In the present study, the enzyme activity of GR and TrxR was investigated in Setaria cervi (S. cervi). Significant activity of both enzymes was detected in the somatic extract of adult and microfilariae stages of S. cervi. Both GR and TrxR were separated by partial purification using ammonium sulfate fractionation and DEAE ion exchange chromatography suggesting the presence of both glutathione and thioredoxin systems in S. cervi. The enzyme glutathione reductase (ScGR) was purified to homogeneity using affinity and ion exchange chromatography that resulted in 90 fold purification with a yield of 11.54%. The specific activity of the ScGR was 643U/mg that migrated as a single band on SDS-PAGE. The subunit molecular mass was determined to be ~50kDa while the optimum pH and temperature were found to be 7.0 and 35°C respectively. The activation energy (Ea) was calculated from the slope of Arrhenius plot as 16.29±1.40kcal/mol. The Km and Vmax were determined to be 0.27±0.045mM; 30.30±1.30U/ml with NADPH and 0.59±0.060mM; 4.16±0.095U/ml with GSSG respectively. DHBA, a specific inhibitor for GR has completely inhibited the enzyme activity at 1μM concentration. The inhibition of ScGR activity with NAI (IC50 0.71mM), NEM (IC50 0.50mM) and DEPC (IC50 0.27mM) suggested the presence of tyrosine, cysteine and histidine residues at its active site. Further studies on characterization and understanding of these antioxidant enzymes may lead to designing of an effective drug against lymphatic filariasis.

Purification of rat kidney glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and glutathione reductase enzymes using 2',5'-ADP Sepharose 4B affinity in a single chromatography step

The enzymes of glucose 6-phosphate dehydrogenase (G6PD), 6-phosphogluconate dehydrogenase (6PGD), and glutathione reductase (GR) were purified from rat kidney in one chromatographic step consisting of the use of the 2',5'-ADP Sepharose 4B by using different elution buffers. This purification procedure was accomplished with the preparation of the homogenate and affinity chromatography on 2',5'-ADP Sepharose 4B. The purity and subunit molecular weights of the enzymes were checked on SDS-PAGE and purified enzymes showed a single band on the gel. The native molecular weights of the enzymes were found with Sephadex G-150 gel filtration chromatography. Using this procedure, G6PG, having the specific activity of 32 EU/mg protein, was purified 531-fold with a yield of 88%; 6PGD, having the specific activity of 25 EU/mg protein, was purified 494-fold with a yield of 73%; and GR, having the specific activity of 33 EU/mg protein, was purified 477-fold with a yield of 76%. Their native molecular masses were estimated to be 144 kDa for G6PD, 110 kDa for 6PGD, and 121 kDa for GR and the subunit molecular weights were found to be 68, 56, and 61 kDa, respectively. A new modified method to purify G6PD, 6PGD, and GR, namely one chromatographic step using the 2',5'-ADP Sepharose 4B, is described for the first time in this study. This procedure has several advantages for purification of enzymes, such as, rapid purification, produces high yield, and uses less chemical materials.

Decreases in binding capacity of the mitochondrial 18 kda translocator protein accompany oxidative stress and pathological signs in rat liver after DMBA exposure

7,12-Dimethylbenz[a]anthracene (DMBA) presents a pollutant implicated in various toxicological effects. The aim of this experiment was to study the effects of DMBA administration on oxidative stress, histopathological signs, and 18 kDa translocator protein (TSPO) binding characteristics in rat liver. We also studied the effects of dose stoichiometry, dose frequency, and duration of protocol of DMBA administration. In this study, rats surviving eighteen weeks after DMBA exposure showed mild to moderate histopathological changes in the liver, mainly characterized by glossy appearance of hepatocytes, heterochromatic nuclei, and glycogen overload in the midzonal region of the hepatic lobe. These changes were accompanied by significant rises in oxidant levels, along with declines in nonenzymic antioxidants, indicating that DMBA induced oxidative stress in the liver. This finding correlated well with decreases in TSPO binding capacity in the liver of the rats in our study. Other studies have shown that TSPO can be affected by oxidative stress, as well as contribute to oxidative stress at mitochondrial levels. Further studies are needed to assay whether the decreases in TSPO density in the liver are part of the damaging effects caused by DMBA or a compensatory response to the oxidative stress induced by DMBA.

Purification and characterization of a glutathione reductase from Phaeodactylum tricornutum

Glutathione reductase (E.C.1.8.1.7) was purified from Phaeodactylum tricornutum cells grown axenically in an autotrophic medium. The overall procedure started with preparation of the cell extract and addition of ammonium sulfate to 20% saturation, followed by anion exchange and affinity interaction chromatography (Blue-A- and 2',5'-ADP-Sepharose). Complete purification required native polyacrylamide gel electrophoresis as the final step. The enzyme was purified to homogeneity and functionally characterized. Its native molecular mass was estimated to be 118 kDa; which corresponds to a dimer. The enzyme exhibited a specific activity of 190 U mg(-1) with an optimal activity at pH 8.0 and 32 degrees C. We determined K(m) values of 14 microM and 60 microM for NADPH and oxidized glutathione, respectively. Products inhibited the enzyme according to a hybrid ping-pong reaction mechanism. After MALDI-TOF analysis, the purified enzyme was unambiguously identified as one of the two proteins annotated as glutathione reductases in the genome of the diatom. The properties of the enzyme help to understand redox metabolic scenarios in P. tricornutum.

Purification and kinetic properties of glutathione reductase from bovine liver

Glutathione reductase (GR, NADPH: oxidized glutathione oxidoreductase, EC 1.6.4.2) catalyzes the reduction of oxidized glutathione (GSSG) to reduced glutathione (GSH) using NADPH as reducing cofactor. The aim of the present work was to purify and characterize GR from bovine liver. GR was purified using 2', 5' ADP-Sepharose 4B and DEAE-Sepharose Fast Flow columns. The enzyme has been purified 5456-fold and with a yield of 38.4%. The molecular and catalytic properties of bovine liver GR have been studied. Optimum temperature and pH was found to be 50 degrees C and 7, respectively. The activation energy of the reaction catalyzed by the enzyme was 9.065 kcal/mole. The molecular weight of the enzyme was found to be 55 kDa by SDS-PAGE. Kinetic characterization of bovine liver GR was also investigated, Km(NADPH) 0.063 +/- 0.008 mM and Km(GSSG) 0.154 +/- 0.015 mM were determined. It is accepted that parallel lines observed in these double reciprocal plots obeys Ping Pong mechanism and we have showed this in our steady state study. According to our results of statistical analysis, the Ping Pong mechanism is a suitable model since the loss function is less than the other mechanisms. However, competitive inhibition by a product could be accepted in sequential mechanisms but not in a Ping Pong mechanism. In this study, kinetic data are consistent with a branching reaction mechanism previously proposed for GR from other sources by other studies.

Purification and properties of glutathione reductase from liver of the anoxia-tolerant turtle, Trachemys scripta elegans

Glutathione reductase (GR) is a homodimeric flavoprotein that catalyzes the reduction of oxidized glutathione (GSSG) using NADPH as a cofactor. The enzyme is a major component of cellular defense mechanisms against oxidative injury. In this study, GR was purified from the liver of the anoxia-tolerant turtle, Trachemys scripta elegans. The overall fold purifications were 13.3- and 12.1-fold with final specific activities of 5.5 and 1.44 U/mg of protein for control and anoxic turtle GR, respectively. SDS-PAGE of purified turtle liver GR showed a single protein band at approximately 55 kDa. Reverse phase HPLC of turtle GR revealed a single peak that had the same retention time as yeast GR. No new isoform of GR was detected in liver of T. s. elegans during anoxia. The K (m) values of turtle GR for GSSG and NADPH was 44.6 and 6.82 microM, respectively, suggesting a substantially higher affinity of turtle GR toward GSSG than most other vertebrates. Unlike other human GR, NADP(+ )did not inhibit turtle GR activity. The activation energy of turtle GR, calculated from the slope of the Arrhenius plot, was 32.2 +/- 2.64 kJ/mol. Turtle GR had high activity under a broad pH range (having activity between pHs 4 and 10; optimal activity at pH 6.5) and the enzyme maintains activity under the pH drop that occurs under anoxic conditions. The high affinity of turtle GR suggests that turtles have high redox buffering capacity of tissues to protect against oxidative stress encountered during anoxia/reoxygenation.

Molecular organization of the glutathione reductase gene in Drosophila melanogaster

Glutathione reductase catalyzes the conversion of the oxidized form of glutathione to regenerate reduced glutathione, which acts as a versatile intracellular reductant. The present study provides initial characterization of the glutathione reductase gene in Drosophila melanogaster and its response to experimentally induced oxidative stress. Drosophila cDNA clones were isolated, based on cross-hybridization to the Musca domestica glutathione reductase cDNA. Genomic clones were isolated by cross-hybridization with the Drosophila cDNA as hybridization probe. Northern analysis of adult Drosophila poly(A)+ RNA, utilizing the Drosophila cDNA probe, revealed a hybridization signal in the 2-kb range. The entire sequence of one cDNA was determined. In addition to a coding domain of 1431 bases, the sequence included 206 bases upstream of a putative start codon and 355 bases downstream of a putative stop codon. Based on the cDNA sequence, the 476 amino acid sequence of the Drosophila glutathione reductase gene was deduced and was found to have extensive similarities with the glutathione reductase gene from other species. Gene mapping of a 13-kb genomic fragment revealed that the glutathione reductase gene consists of at least two exons spanning approximately 5 kb. A first exon contains sequence for only the first 5 amino acids and the first base of the sixth and appears to be separated by a ca. 2.5-kb intron from the remainder of the coding region, which is confined to <2 kb. The Drosophila glutathione reductase is single copy and its cytogenetic position, as determined by in situ hybridization, is 7D-E on the X chromosome. mRNA levels of glutathione reductase, measured by RT-PCR, increased in response to exposure to 100% ambient oxygen by almost twofold and administration of paraquat by greater than threefold. Exposure of flies to hyperoxia also induced a 60% increase in the activity of glutathione reductase and augmented the concentration of total glutathione by ca. 40% following an initial drop. The present study, besides providing an initial molecular characterization of the glutathione reductase gene in Drosophila, demonstrates its dynamic involvement in response to experimentally induced oxidative stress.

Methods for purification of glutathione peroxidase and related enzymes

The different preparative techniques and related analytical methods used for purification of glutathione peroxidase, glutathione transferase and glutathione reductase, described in papers published in the last ten years, have been reviewed in this article. Among the different purification techniques, chromatography has played a relevant role, being reported in all the papers reviewed, whereas other preparative techniques such as electrophoresis and isoelectric focusing were less employed and have been reported in only ca. 3% of cases. Frequently, several different chromatographic modes and several rechromatography steps have been employed. The use of at least three different chromatographic modes has been reported in 53% of total reviewed papers, whereas 41% of them employed two differents modes and in only 6% a single preparative chromatographic step was used. To evaluate losses and improve recovery, analytical methods for quantitation of protein and assay of enzymatic activity must be used in each purification step. Among these analytical techniques, gel electrophoresis, under denaturing conditions, has been widely used to assess purity of enzyme preparation. A discussion of the different activity assay methods used for these three enzymes is also presented in this article.

Methods for chromatographic and electrophoretic separation and assay of NADP oxidoreductases

The different techniques described in purification protocols for pyridine nucleotide-dependent enzymes have been reviewed, covering mainly the papers published in the past six years. Chromatography was reported in 100% of reviewed papers and among the chromatographic techniques, affinity chromatography was the most used (ca. 92%), followed by ion-exchange chromatography (ca. 79%), size-exclusion chromatography (ca. 64%) and hydrophobic chromatography (ca. 24%). Other chromatographic techniques were used infrequently. Each chromatographic technique has a different specific capacity and chemical selectivity and, therefore, the order of selection should be based on a precise knowledge of the nature of the sample and the amount of the target enzyme that it contains. Analytical electrophoresis was used in about 95% of the reviewed papers, with denaturing polyacrylamide gel electrophoresis (PAGE) being the most widely used mode (ca. 92%), followed by native PAGE (ca. 48%). The use of isoelectric focusing was reported in 14% of the papers, while preparative gel electrophoresis was used in only 8% of the cases. The use of other electrophoretic techniques was reported in only a few papers. The use of continuous enzymatic activity assay methods (spectrophotometric) was found in most papers, while high-performance liquid chromatography-based methods (discontinuous assays) were reported in only 11% of the reviewed articles.

Regulation of horse-liver glutathione reductase

1. The enzyme was rapidly inactivated by NAD(P)H, GSH, dithionite or borohydride, while activity increased in the presence of NAD(P)+ or GSSG. NADH was more efficient for inactivation than NADPH. Redox inactivation required neutral or alkaline pH, was maximal at pH 8.5, and depended on the presence of metal cations. 2. GSSG and dithiothreitol fully protected the enzyme from inactivation at concentrations stoichiometric with NAD(P)H. Ten-fold higher ferricyanide or GSH concentrations were required to obtain partial protection. NAD+ or NADP+ were quite ineffective. 3. GSSG fully reactivated the inactive enzyme at 38 degrees C and neutral to acidic pH (5.5-7.5). Reactivation by dithiothreitol was accomplished in short periods of time at pH 8.5 although the activity was progressively lost afterwards. Ferricyanide and GSH also reactivated the enzyme to different extents.

Purification and properties of bovine thioredoxin system

Using a variety of chromatographic techniques, a crude extract from bovine liver was fractionated to obtain pure preparations of thioredoxin reductase, thioredoxin, glutaredoxin and glutathione reductase with good yields. The turbidimetric assay of thioredoxin with insulin as the disulfide substrate was optimized; by incorporation of the lag time (tau) into the calculations, linearity was maintained for a wider range of thioredoxin concentrations, and a distinction could be made between reduced and non-reduced forms. Subunit composition and molecular mass, absorption spectrum and kinetic parameters of thioredoxin reductase were similar to those of other mammalian thioredoxin reductases. By chromatofocusing, two peaks of activity were detected at pH 5.5 and 5.8. Structural changes undergone by the thioredoxin molecule upon oxido-reduction were detected by isoelectric focusing, with a shift of 0.1 pH unit of its pI, and by analytical anion exchange chromatography, with a conspicuous shift of its retention time. These two methods also revealed the presence of a form of thioredoxin not undergoing the above mentioned redox-mediated structural shifts that accounted for > 75% of the total activity.