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PubMed1982

Transport of ascorbate into guinea pig liver mitochondria.

The amount of ascorbate associated with guinea pig liver mitochondria was estimated by high-performance liquid chromatography. Incubation of mitochondria with ascorbate revealed a time-dependent and temperature-dependent accumulation of the vitamin. A steady-state level of ascorbate was obtained in the mitochondria after about 20 min of incubation at 37 degrees C, whereas no accumulation was observed at 0 degrees C. The matrix concentration of ascorbate was highly correlated to the concentration of ascorbate in the incubation medium. The initial rate of accumulation (about 7 pmol/mg protein per min at 10 degrees C) was three orders of magnitude less than for compounds that are transported across the mitochondrial inner membrane by specific carriers. Experiments with the enzyme ascorbate oxidase demonstrated that the mitochondrial membrane is also permeable to dehydroascorbate, and that the accumulated dehydroascorbate is stable in the mitochondria. There was no effect of the energy state of the mitochondrial membrane of the initial transport rate of ascorbate. Electrostatic binding of ascorbate to the membrane was excluded from experiments performed in isosmotic potassium chloride medium. Diffusion of ascorbate across the mitochondrial inner membrane accounts for the experimental findings.

Animals↗
PubMed1991

Glutathione deficiency decreases tissue ascorbate levels in newborn rats: ascorbate spares glutathione and protects.

Glutathione deficiency in newborn rats, produced by administration of L-buthionine-(S,R)-sulfoximine, a transition-state inactivator of gamma-glutamylcysteine synthetase, decreases ascorbate levels of kidney, liver, brain, and lung. These tissues, especially their mitochondria, undergo severe damage and the animals die within a few days. When glutathione levels are markedly decreased, ascorbate levels decrease leading to formation of dehydroascorbate, which is degraded. Ascorbate has high antioxidant activity, but it (and other antioxidants such as alpha-tocopherol) must be maintained in reduced forms. These studies show in vivo that an important function of glutathione is to maintain tissue ascorbate. Administration of large doses of ascorbate (but not of dehydroascorbate) to buthionine sulfoximine-treated newborn rats decreases mortality, leads to normal levels of ascorbate, and spares glutathione. Newborn rats given lower doses of buthionine sulfoximine develop cataracts that, as shown previously, can be prevented by giving glutathione monoester; as found here, such cataracts can be partially prevented by administration of high doses of ascorbate or dehydroascorbate. Ascorbate spares glutathione indicating that these compounds have similar antioxidant actions. Ascorbate may have reductive functions that are not efficiently performed by glutathione. Although glutathione normally functions to maintain ascorbate, alpha-tocopherol, and other cellular components in reduced states, ascorbate can serve as an essential antioxidant in the presence of severe glutathione deficiency.

Animals↗
PubMed2006

Genetic control of fruit vitamin C contents.

An F(1) progeny derived from a cross between the apple (Malus x domestica) cultivars Telamon and Braeburn was used to identify quantitative trait loci (QTL) linked to the vitamin C (l-ascorbate [l-AA]) contents of fruit skin and flesh (cortex) tissues. We identified up to three highly significant QTLs for both the mean l-AA and the mean total l-AA contents of fruit flesh on both parental genetic linkage maps, confirming the quantitative nature of these traits. These QTLs account for up to a maximum of 60% of the total population variation observed in the progeny, and with a maximal individual contribution of 31% per QTL. QTLs common to both parents were identified on linkage groups (LGs) 6, 10, and 11 of the Malus reference map, while each parent also had additional unique QTLs on other LGs. Interestingly, one strong QTL on LG-17 of the Telamon linkage map colocalized with a highly significant QTL associated with flesh browning, and a minor QTL for dehydroascorbate content, supporting earlier work that links fruit l-AA contents with the susceptibility of hardfruit to postharvest browning. We also found significant minor QTLs for skin l-AA and total l-AA (l-AA + dehydroascorbate) contents in Telamon. Currently, little is known about the genetic determinants underlying tissue l-AA homeostasis, but the presence of major, highly significant QTL in both these apple genotypes under field conditions suggests the existence of common control mechanisms, allelic heterozygosity, and helps outline strategies and the potential for the molecular breeding of these traits.

Ascorbic Acid↗
PubMed1998

Vitamin C protects human arterial smooth muscle cells against atherogenic lipoproteins: effects of antioxidant vitamins C and E on oxidized LDL-induced adaptive increases in cystine transport and glutathione.

Glutathione (GSH) plays a key role in cellular antioxidant defenses by scavenging reactive oxygen species and reducing lipid peroxides. Intracellular GSH levels are regulated by transport of its precursor L-cystine via system xc-, which can be induced by oxidant stress. As oxidatively modified low density lipoproteins (LDLs) contribute to impaired vascular reactivity and the formation of atherosclerotic lesions, we have examined the effects of oxidized LDL and the antioxidant vitamins C and E on the L-cystine-GSH pathway in human umbilical artery smooth muscle cells (HUASMCs). Oxidized LDL, but not native LDL, elevated intracellular GSH levels and L-cystine transport via system xc- in a time-dependent (up to 24 hours) and dose-dependent (10 to 100 microg x mL-1) manner. These increases were dependent on protein synthesis and the extent of LDL oxidation, but the induction of L-cystine transport activity was independent of GSH synthesis. Pretreatment of HUASMCs for 24 hours with vitamin E (100 micromol/L) attenuated oxidized LDL-mediated increases in GSH, whereas pretreatment with vitamin C depressed basal levels and abolished oxidized LDL-induced increases in GSH and L-cystine transport in a time-dependent (3 to 24 hours) and dose-dependent (10 to 100 micromol/L) manner. Pretreatment of cells with dehydroascorbate had no effect on oxidized LDL-mediated increases in L-cystine transport and only marginally attenuated increases in GSH. Our findings provide the first evidence that vitamin C spares endogenous adaptive antioxidant responses in human vascular smooth muscle cells exposed to atherogenic oxidized LDL.

Antioxidants↗
PubMed1999

Ascorbate-mediated electron transfer in protein thiol oxidation in the endoplasmic reticulum.

Addition of, or gulonolactone oxidase-dependent in situ generation of, ascorbate provoked the oxidation of protein thiols, which was accompanied by ascorbate consumption in liver microsomal vesicles. The maximal rate of protein thiol oxidation was similar upon gulonolactone, ascorbate or dehydroascorbate addition. Cytochrome P450 inhibitors (econazole, proadifen, quercetin) decreased ascorbate consumption and the gulonolactone or ascorbate-stimulated thiol oxidation. The results demonstrate that the ascorbate/dehydroascorbate redox couple plays an important role in electron transfer from protein thiols to oxygen in the hepatic endoplasmic reticulum, even in gulonolactone oxidase deficient species.

Animals↗
PubMed2005

Identification of proteins induced or upregulated by Fusarium head blight infection in the spikes of hexaploid wheat (Triticum aestivum).

Fusarium head blight (FHB) caused by Fusarium graminearum is a destructive disease of wheat and barley. It causes economic losses due to reduction in both yield and quality. Although FHB resistance has been well documented and resistant cultivars have been developed to reduce incidence and severity of FHB, there is a limited understanding of the molecular mechanisms involved in plant resistance against the infection and spread of F. graminearum. In the current study, 2-dimensional displays of proteins extracted from wheat spikelets infected with F. graminearum were compared with those from spikelets inoculated with sterile H2O. Fifteen protein spots were detected that were either induced (qualitatively different) or upregulated (quantitatively increased) following F. graminearum infection of spikelets of 'Ning7840', a resistant cultivar. These proteins were identified by LC-MS/MS analysis. Proteins with an antioxidant function such as superoxide dismutase, dehydroascorbate reductase, and glutathione S-transferases (GSTs) were upregulated or induced 5 d after inoculation with F. graminearum, indicating an oxidative burst of H2O2 inside the tissues infected by FHB. An ascorbate-glutathione cycle is likely involved in reduction of H2O2. Expression of proteins with highest similarity to dehydroascorbate reductase and TaGSTF5 (a glutathione S-transferase) differed following FHB infection in susceptible and resistant cultivars. A 14-3-3 protein homolog was also upregulated in FHB-infected spikelets. In addition, a PR-2 protein (beta-1, 3 glucanase) was upregulated in FHB-infected spikes, which is in accord with a previous study that analyzed transcript accumulation.

Amino Acid Sequence↗
PubMed2000

Ascorbate-dependent recycling of the vitamin E homologue Trolox by dihydrolipoate and glutathione in murine skin homogenates.

In the redox antioxidant network, dihydrolipoate can synergistically enhance the ascorbate-dependent recycling of vitamin E. Since the major endogenous thiol antioxidant in biological systems is glutathione (GSH) it was of interest to compare the effects of dihydrolipoate with GSH on ascorbate-dependent recycling of the water-soluble homologue of vitamin E, Trolox, by electron spin resonance (ESR). Trolox phenoxyl radicals were generated by a horseradish peroxidase (HRP)-hydrogen peroxide (H2O2) oxidation system. In the presence of dihydrolipoate, Trolox radicals were suppressed until both dihydrolipoate and endogenous levels of ascorbate in skin homogenates were consumed. Similar experiments made in the presence of GSH revealed that Trolox radicals reappeared immediately after ascorbate was depleted and that GSH was not able to drive the ascorbate-dependent Trolox recycling reaction. However, at higher concentrations GSH was able to increase ascorbate-mediated Trolox regeneration from the Trolox radical. ESR and spectrophotometric measurements demonstrated the ability of dihydrolipoate or GSH to react with dehydroascorbate, the two-electron oxidation product of ascorbate in this system. Dihydrolipoate regenerated greater amounts of ascorbate at a much faster rate than equivalent concentrations of GSH. Thus the marked difference between the rate and efficiency of ascorbate generation by dihydrolipoate as compared with GSH appears to account for the different kinetics by which these thiol antioxidants influence ascorbate-dependent Trolox recycling.

Animals↗
PubMed1991

Effect of calf housing on plasma ascorbate and endocrine and immune function.

The effect of housing calves in indoor metal pens (1.2 m x 1.2 m) or commercial calf hutches was determined on plasma concentration of cortisol, antibodies, and ascorbate. Six calves per treatment were deprived of colostrum, assigned randomly to treatment, and fed a commercial milk replacer until 56 d of age. Calves housed in hutches had higher plasma IgG concentrations than calves in pens at 42 and 56 d of age. Housing had no effect on plasma IgM concentration. Antibody titers to keyhole limpet hemocyanin injected at 14 and 28 d of age were higher in hutch-housed calves from 21 to 56 d of age. Calves housed in hutches also had lower plasma cortisol concentrations, although cortisol decreased with age in both treatment groups. Plasma ascorbate and ascorbate plus dehydroascorbate were higher in hutch-housed calves. Regression analysis indicated a positive relationship between plasma ascorbate and IgG in metal penhoused calves and a negative relationship in hutch-housed calves. Housing in 1.2 m x 1.2 m metal pens decreases cortisol, plasma ascorbate, IgG, and specific antibody titers in dairy calves relative to calves housed in hutches.

Aging↗
PubMed1990

Ascorbate free radical stimulates the growth of a human promyelocytic leukemia cell line.

Ascorbate free radical stimulates the growth of human promyelocytic leukemia cells (HL-60) in the presence of a limited amount of serum (1%) when added to the cells under conditions where it is impermeable. Maximum growth stimulation occurs at concentrations from 5 x 10(-9) to 2 x 10(-8) M. Ascorbate mimicks the stimulation effect of its free radical but stimulates at higher concentrations. Autoxidation of ascorbate by oxygen produces its free radical, which apparently causes growth stimulation. Ascorbate could be regenerated by intact cells in vitro, since prevention of autoxidation of ascorbate in the presence of cells is observed. Neither dehydroascorbate nor isoascorbate increases HL-60 cell growth. Short term incubation of cells in the presence of ascorbate free radical induced intracellular NADH oxidation. We propose that the stimulation of growth of HL-60 cells shown here could be caused by activation of the transplasma membrane electron transport system by the ascorbate free radical.

Ascorbic Acid↗
PubMed1985

The role of glutathione and ascorbate in hydroperoxide removal in cyanobacteria.

The antioxidative potential of cyanobacteria to scavenge hydroperoxides formed as by-products of photosynthetic activity was investigated in Nostoc muscorum 7119 and Synechococcus 6311. These cells contained a high concentration of glutathione, 2-5 mM, and a low concentration of ascorbate, 20-100 uM. No glutathione peroxidase was detected while the activity of ascorbate peroxidase was high, reacting with hydrogen peroxide, t-butyl hydroperoxide, and cumene hydroperoxide. Dehydroascorbate reductase was active in recycling ascorbate and glutathione reductase regenerated glutathione from glutathione disulphide. The activity of these antioxidative enzymes in the cyanobacteria was sufficient to remove between 60-230 nmoles H2O2 .mg protein-1 min-1. It is suggested that in cyanobacteria an effective reaction sequence for removal of hydroperoxides involves ascorbate peroxidase and recycling of glutathione and ascorbate.

Ascorbate Peroxidases↗
PubMed1993

Glutathione ester delays the onset of scurvy in ascorbate-deficient guinea pigs.

Previous studies showed that administration of ascorbate to glutathione (GSH)-deficient newborn rats and guinea pigs prevented toxicity and mortality and led to increased tissue and mitochondrial GSH levels; ascorbate thus spares GSH. In the present work, we tried to answer the converse question: Does administration of GSH spare ascorbate? Because administered GSH is not well transported into most cells, we gave GSH monoethyl ester (which is readily transported and converted into GSH intracellularly) to guinea pigs fed an ascorbate-deficient diet. We found that treatment with GSH ester significantly delays appearance of the signs of scurvy and that this treatment spares ascorbate; thus, the decrease of tissue levels of ascorbate was delayed. The findings support the conclusions that (i) GSH is essential for the physiological function of ascorbate because it is required in vivo for reduction of dehydroascorbate and (ii) there is metabolic redundancy and overlap of the functions of these antioxidants. The sparing effect of GSH in scurvy may be mediated through an increase in the reduction of dehydroascorbate (which would otherwise be degraded) and to antioxidant effects of GSH that are also produced by ascorbate. Other studies indicate that GSH deficiency in adult mice stimulates ascorbate synthesis in liver. During this work we found that administration of GSH itself is highly toxic to ascorbate-deficient guinea pigs when given in divided i.p. doses totaling 3.75 mmol/kg daily.

Animals↗
PubMed2001

Cloning and expression of a novel human glutaredoxin (Grx2) with mitochondrial and nuclear isoforms.

Glutaredoxin (Grx) is a glutathione-dependent hydrogen donor for ribonucleotide reductase. Today glutaredoxins are known as a multifunctional family of GSH-disulfide-oxidoreductases belonging to the thioredoxin fold superfamily. In contrast to Escherichia coli and yeast, a single human glutaredoxin is known. We have identified and cloned a novel 18-kDa human dithiol glutaredoxin, named glutaredoxin-2 (Grx2), which is 34% identical to the previously known cytosolic 12-kDa human Grx1. The human Grx2 sequence contains three characteristic regions of the glutaredoxin family: the dithiol/disulfide active site, CSYC, the GSH binding site, and a hydrophobic surface area. The human Grx2 gene, located at chromosome 1q31.2--31.3, consisted of five exons that were transcribed to a 0.9-kilobase human Grx2 mRNA ubiquitously expressed in several tissues. Two alternatively spliced Grx2 mRNA isoforms that differed in their 5' region were identified. These corresponded to alternative proteins with a common 125-residue C-terminal Grx domain but with different N-terminal extensions of 39 and 40 residues, respectively. The 125-residue Grx domain and the two full-length variants were expressed in E. coli and exhibited GSH-dependent hydroxyethyl disulfide and dehydroascorbate reducing activities. Western blot analysis of subcellular fractions from Jurkat cells with a specific anti-Grx2 antibody showed that human Grx2 was predominantly located in the nucleus but also present in the mitochondria. We further showed that one of the mRNA isoforms corresponding to Grx2a encoded a functional N-terminal mitochondrial translocation signal.

Amino Acid Sequence↗
PubMed2006

Detection of an antioxidant profile in the human brain in vivo via double editing with MEGA-PRESS.

Vitamin C (ascorbate) and glutathione (GSH) are the two most concentrated non-enzymatic antioxidants in the human brain. Double editing with (DEW) MEGA-PRESS at 4T was designed in this study to measure both antioxidants in the same amount of time previously required to measure one. In the occipital lobe of four human subjects, resolved ascorbate (Asc) and GSH resonances were detected repeatedly and simultaneously using DEW MEGA-PRESS. The Asc and GSH concentrations measured using LCModel analysis of DEW MEGA-PRESS spectra were 0.8 +/- 0.1 and 1.0 +/- 0.1 micromol/g (mean +/- SD), with average Cramer-Rao lower bounds (CRLB) of 10% and 7%, respectively. Aside from the effects of J-modulation at a common echo time (TE), double editing did not compromise sensitivity. To determine the extent to which the oxidized forms of Asc and GSH contribute to DEW MEGA-PRESS spectra in vivo, chemical shifts and coupling constants for dehydroascorbate (DHA) and oxidized glutathione (GSSG) were measured at physiologic pH and temperature. DHA does not contribute to the 3.73 ppm DEW MEGA-PRESS Asc resonance. GSSG contributions to the DEW MEGA-PRESS GSH resonance (3.0 ppm) are negligible under physiologic conditions, and would be evidenced by a distinct GSSG resonance (3.3 ppm) at exceptionally high concentrations.

Adult↗
PubMed2002

Evidence for the presence and activity of a complete antioxidant defence system in mature sieve tubes.

The phloem is the major route for the transport of solutes and nutrients from source to sink organs in plants. The functional transport phloem consists of parenchymal tissue, enucleate sieve elements, and the intimately connected companion cells. The general absence of a nucleus and functional ribosomes in sieve tubes poses problems especially for damage avoidance and repair of sieve element components. To examine how sieve tubes can remain functional during oxidative stress, we analysed phloem sap of cucumber and pumpkin plants with respect to the presence of antioxidant defence enzymes, their enzymatic activity, and activity changes after exposure to drought stress. Using 1D SDS-PAGE and nano ESI MS/MS, the presence of proteins such as cytosolic Cu/Zn superoxide dismutase, monodehydroascorbate reductase, and peroxidase could be shown. Moreover, activities for several antioxidant enzymes (superoxide dismutase, dehydroascorbate reductase, peroxidase) in phloem exudate could be demonstrated. The activity of these enzymes in phloem sap from cucumber and pumpkin plants increased in response to drought stress. The presented results together with earlier findings provide evidence supporting the presence of a complete machinery of antioxidant defence enzymes and detoxifying metabolites important for avoiding damage to essential components of the sieve elements due to oxidative stress.

Amino Acid Sequence↗
PubMed1996

Vaccinia virus G4L gene encodes a second glutaredoxin.

Vaccinia virus (VV) was previously shown to encode a functional glutaredoxin, the product of the o2l gene, which is synthesized late in infection, after the onset of DNA replication. Here we report that an open reading frame in the VV genome designated as g4l encodes a protein that has sequence similarity to glutaredoxins and possesses thioltransferase and dehydroascorbate reductase activities. G4L protein in infected cells can be detected as early as 4 hr after infection and is constitutively expressed up to 24 hr postinfection. A protein homologous to G4L and retaining the predicted glutaredoxin active center is encoded by the recently sequenced Molluscum Contagiosum virus (MCV), whereas O2L protein is not conserved, suggesting that the glutaredoxin activity of G4L may be involved in replication of all poxviruses.

Amino Acid Sequence↗
PubMed2005

Fungal pathogen-induced changes in the antioxidant systems of leaf peroxisomes from infected tomato plants.

Peroxisomes, being one of the main organelles where reactive oxygen species (ROS) are both generated and detoxified, have been suggested to be instrumental in redox-mediated plant cell defence against oxidative stress. We studied the involvement of tomato (Lycopersicon esculentum Mill.) leaf peroxisomes in defence response to oxidative stress generated upon Botrytis cinerea Pers. infection. The peroxisomal antioxidant potential expressed as superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6) and glutathione peroxidase (GSH-Px, EC 1.11.1.19) as well as the ascorbate-glutathione (AA-GSH) cycle activities was monitored. The initial infection-induced increase in SOD, CAT and GSH-Px indicating antioxidant defence activation was followed by a progressive inhibition concomitant with disease symptom development. Likewise, the activities of AA-GSH cycle enzymes: ascorbate peroxidase (APX, EC 1.11.1.11), monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1) and glutathione reductase (GR, EC 1.6.4.2) as well as ascorbate and glutathione concentrations and redox ratios were significantly decreased. However, the rate and timing of these events differed. Our results indicate that B. cinerea triggers significant changes in the peroxisomal antioxidant system leading to a collapse of the protective mechanism at advanced stage of infection. These changes appear to be partly the effect of pathogen-promoted leaf senescence.

Antioxidants↗
PubMed1997

Cloning of the cDNA for glutaredoxin, an abundant sieve-tube exudate protein from Ricinus communis L. and characterisation of the glutathione-dependent thiol-reduction system in sieve tubes.

Sieve-tube exudate protein (STEP) from Ricinus communis L. seedlings consists of a characteristic set of more than 100 different polypeptides, against which a complex antiserum was raised. This antiserum cross-reacted with dominant protein species (molecular weights 10-30 kDa) present in the sieve-tube exudate and, to a lesser extent, with proteins in tissue extracts of Ricinus and a wide range of other plant species. For further elucidation of the nature of individuals STEPs in the sieve tubes the anti-STEP serum was used to screen a cDNA expression library constructed from Ricinus cotyledon mRNA. Two clones that differed in the 3' untranslated region encoded a protein of 11 kDa which showed striking homology to bacterial and eucaryotic glutaredoxin sequences. Glutaredoxin activity was confirmed for the recombinant protein after overexpression in Escherichia coli and characterised in detail in sieve-tube exudate. Michaelis Menten constants (Km) for reduced glutathione and cysteine were 2 mM and 50 microns, respectively. Besides L-cysteine, dehydroascorbate and protein disulphides were also reduced by the activity present in the sieve-tube exudate. Glutathione, which is the obligate donor of reduced thiols for glutaredoxin, was present in sieve-tube sap in millimolar concentrations (up to 3 mM) with a ratio of total to oxidised glutathione of 3:1. It is suggested that glutaredoxin and glutathione in sieve tubes prevent oxidative damage and may be involved in redox regulation of sieve-tube proteins.

Amino Acid Sequence↗
PubMed2005

Changes in the ascorbate system in the response of pumpkin (Cucurbita pepo L.) roots to aluminium stress.

The involvement of the ascorbate (AsA) system in the response of pumpkin (Cucurbita pepo L.) roots to aluminium stress was studied. The treatment of 5-day-old pumpkin seedlings with 50 microM aluminium sulphate resulted in approximately 60% inhibition of root growth within 48-60 h of treatment, while aluminium accumulated in the roots reaching a maximum within 48h. During the same period, the hydrogen peroxide content of the roots was strongly enhanced. The increased level of hydrogen peroxide was matched by both increased ascorbate peroxidase (APX) (EC 1.11.1.11) activity and ascorbate free radical reductase (AFRR) (EC 1.1.5.4) activity, while dehydroascorbate reductase (DHAR) (EC 1.8.5.1) and glutathione reductase (GR) (EC 1.6.4.2) did not change. The levels of AsA in the roots were also increased by the Al treatment. It was concluded that an oxidative burst is probably involved in the toxicity of Al in pumpkin roots and that plants react to the enhanced production of reactive oxygen species by expressing higher levels of scavenging systems such as the AsA-APX system.

Alum Compounds↗