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PubMed2007

Differential expression of the ascorbate oxidase multigene family during fruit development and in response to stress.

Ascorbate oxidase (AO, EC 1.10.3.3) is a member of the multicopper oxidases family. It catalyzes the oxidation of ascorbic acid (AA) to dehydroascorbic acid (DHA) via monodehydroascorbate (MDHA), with the concomitant reduction of molecular oxygen to water. In melon (Cucumis melo), ascorbate oxidase is encoded by a multigene family comprising at least four genes. Here, we present the detailed characterization of two melon AO genes, CmAO1 and CmAO4. Gene-specific expression studies of the AO gene family in melon revealed that only CmAO1 and CmAO4 are transcriptionally active and differentially regulated dependent on tissue, developmental stage and external stimuli. Transcripts of the CmAO1 gene are present in floral and fruit tissues, whereas CmAO4 mRNA preferentially accumulates in vegetative tissues. CmAO genes were not detected in melon seeds, but CmAO4 expression is activated upon germination. CmAO4 mRNA steady-state levels are also regulated in response to wounding and heat stress, by hormones (abscisic acid, salicylic acid and jasmonates), AA and copper. These findings suggest that AO gene expression is transcriptionally regulated during fruit development and in response to hormonal cues associated with the control of cell growth and the stress response.

Adaptation, Physiological↗
PubMed1985

Determination of ascorbic acid with immobilized green zucchini ascorbate oxidase.

Ascorbate oxidase from zucchini squash was immobilized onto CH-Sepharose via carbodiimide. The properties of the immobilized enzyme were found to be similar to those of the free ascorbate oxidase. The immobilized enzyme was utilized in a flow-through system equipped with a polarographic detector which monitors the oxygen depletion due to the reaction ascorbic acid + 1/2 O2----dehydroascorbic acid + H2O. This method, the response of which is linear between 3 X 10(-7) and 5 X 10(-4) M ascorbate, was utilized to measure the ascorbic acid in biological samples such as human plasma and fruit juices at a rate of about 60 determinations every hour with a standard deviation lower than 5%.

Ascorbate Oxidase↗
PubMed1991

Investigations into the relationship between the dopaminergic system and ascorbic acid in rat striatum.

Levels of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), ascorbic acid (AA) and dehydroascorbic acid (DHAA) were determined by HPLC in the striatum of male Wistar rats after single or repeated injections of apomorphine (1 mg/kg/day s.c.) and/or haloperidol (1 mg/kg/day i.p.), and 24 h after the last drug administration. Apomorphine significantly reduced the DOPAC/DA ratio and increased the DHAA/AA ratio; these ratio changes were significantly correlated (r = -0.9969, P less than 0.0005). Haloperidol greatly increased the DOPAC/DA ratio; the DHAA/AA ratio was also slightly increased, but there was no significant correlation. When apomorphine was associated with haloperidol, the resulting DOPAC/DA ratio was significantly lower than after haloperidol alone; the DHAA/AA ratio was also significantly reduced in contrast to the effect of apomorphine alone. It is concluded that a non-selective DA receptor activation mediates, in a correlated way, both the inhibition of DA turnover and the increase of AA oxidation in the rat striatum.

Animals↗
PubMed2006

Seasonal profiles of leaf ascorbic acid content and redox state in ozone-sensitive wildflowers.

Cutleaf coneflower (Rudbeckia laciniata L.), crown-beard (Verbesina occidentalis Walt.), and tall milkweed (Asclepias exaltata L.) are wildflower species native to Great Smoky Mountains National Park (U.S.A.). Natural populations of each species were analyzed for leaf ascorbic acid (AA) and dehydroascorbic acid (DHA) to assess the role of ascorbate in protecting the plants from ozone stress. Tall milkweed contained greater quantities of AA (7-10 micromol g(-1) fresh weight) than crown-beard (2-4 micromol g(-1) fresh weight) or cutleaf coneflower (0.5-2 micromol g(-1) fresh weight). DHA was elevated in crown-beard and cutleaf coneflower relative to tall milkweed suggesting a diminished capacity for converting DHA into AA. Tall milkweed accumulated AA in the leaf apoplast (30-100 nmol g(-1) fresh weight) with individuals expressing ozone foliar injury symptoms late in the season having less apoplast AA. In contrast, AA was not present in the leaf apoplast of either crown-beard or cutleaf coneflower. Unidentified antioxidant compounds were present in the leaf apoplast of all three species. Overall, distinct differences in antioxidant metabolism were found in the wildflower species that corresponded with differences in ozone sensitivity.

Air Pollutants↗
PubMed1989

Active transport of ascorbic acid into lens epithelium of the rat.

The transport rates of radiolabeled ascorbic acid (AA) and dehydroascorbic acid, as well as 3-O-methyl-D-glucose and L-glucose from blood into aqueous humor, lens epithelium and lens 'cortex' compartments were studied in male Sprague-Dawley rats. In vivo pulse chase kinetic studies and modeling of transport from plasma and aqueous and on into idealized water compartments of lens epithelium and cortex allowed for the calculation of transport rate constants, Ki (min-1), in experiments utilizing L-glucose as a passive internal control. TLC chromatography was used to monitor intraocular labeled molecules deriving from labeled test molecules introduced via blood. Results indicate that AA enters aqueous humor at rates similar to L-glucose and likely via simple passive diffusion. In contrast, an active uptake of AA by lens epithelium was found with the calculated entry constant for ascorbate being more than 21 times faster than that of L-glucose. Concentrations in lens epithelium were found to be more than twice that of aqueous humor within only 7 min from the introduction of a [14C]AA bolus into blood. It was also found that very little AA continued on past the epithelium to the interior lens cortex compartment. Our data suggest no special uptake of AA by lens fiber cells. The non-metabolizable analog of D-glucose, 3-O-methyl-D-glucose, however, readily moves past the lens epithelium into fiber cells at much faster rates than the passive L-glucose marker and in a manner consistent with facilitated diffusion. The data suggest that even in a nocturnal species, such as a rat, which demonstrates relatively low circulating levels of ascorbic acid in plasma and aqueous humor, special mechanisms exist for moving ascorbic acid into intraocular tissues. More specifically, the lens epithelium actively takes up ascorbate for some, as yet unclear purpose while the interior fiber cells appear to have no special uptake mechanism for this molecule.

Animals↗
PubMed2003

L-galactono-gamma-lactone dehydrogenase aand vitamin C content in fresh-cut potatoes stored under controlled atmospheres.

L-galactono-gamma-lactone dehydrogenase (GLDH) activity and vitamin C content as ascorbic acid (AA) plus dehydroascorbic acid (DHA) were evaluated in five potato tuber cultivars (Agata, Altesse, Franceline, Manon, and Monalisa). The effect of fresh-cutting and subsequent refrigerated storage of Manon potato under different atmospheres (air, 20% CO(2) + air, 100% N(2), and vacuum packaging) on GLDH activity and vitamin C content was also determined. GLDH from the five potato tuber cultivars showed typical inhibition kinetics by high substrate concentration in the synthesis of AA from its physiological precursor L-galactonic acid-gamma-lactone (GL). GLDH activity was not correlated with the corresponding vitamin C content in any potato tuber cultivar. GLDH from all the cultivars presented a major isoform with isoelectric point (IEP) 5, which changed to IEP = 4.3 after minimal processing. In addition, the GLDH-catalyzed synthesis of AA by the new isoform showed typical Michaelis kinetics, in which the enzyme became more efficient to catalyze the reaction. Whether the change in the isoform pattern was due to either post-translational modifications or de novo synthesis of a new isoenzyme remains unanswered. Fresh-cutting increased GLDH activity from 4.7-fold (vacuum packaging) to 11-fold (air) after 6 days. In addition, 100% of vitamin C content was retained in air and decreased in the rest of atmospheres after this storage period, following the sequence vacuum packaging (89%) > 100% N(2) (78%) > 20% CO(2) + air (63%). This tendency was correlated with the corresponding GLDH activity detected in each storage atmosphere, except in the case of 20% CO(2) + air. Vacuum packaging proved to be the best storage condition, because fresh-cut potatoes did not turn brown and retained 89% of initial vitamin C content.

Air↗
PubMed2006

Fast analysis of sugars, fruit acids, and vitamin C in sea buckthorn (Hippophaë rhamnoides L.) varieties.

A fast, one-step gas chromatographic method was developed to analyze trimethylsilyl (TMS) derivatives of sugars, fruit acids, and ascorbic acid in sea buckthorn (Hippohaë rhamnoides L.) berries. The method was applied to berry press juice of sea buckthorn of different origins grown in Finland during the 2003 and 2004 seasons. The method gave reliable results for D-fructose, D-glucose, ethyl-D-glucose, and malic, quinic, and ascorbic acids, which are the major sugars and acids in sea buckthorn juice. For the first time in sea buckthorn and evidently in any berry, the presence of ethyl beta-D-glucopyranoside is reported. The structure of ethyl glucose was verified by high-performance liquid chromatography (HPLC), gas chromatography (GC), MS, and NMR analyses of both the isolated and the synthesized compounds. In the GC method, vitamin C was analyzed as ascorbic acid only, and dehydroascorbic acid was thus not taken into account.

Ascorbic Acid↗
PubMed1998

Age-associated decline in ascorbic acid concentration, recycling, and biosynthesis in rat hepatocytes--reversal with (R)-alpha-lipoic acid supplementation.

Ascorbic acid recycling from dehydroascorbic acid and biosynthesis from gulono-1,4-lactone were used as measures of cellular response capacity to increased oxidative stress induced by tert-butylhydroperoxide. The hepatic ascorbic acid concentration was 54% lower in cells from old rats when compared to cells isolated from young rats (P<0.0005). Freshly isolated hepatocytes from old rats exhibited a significantly decreased ascorbic acid recycling capacity in response to oxidative stress (P<0.005) compared to cells from young rats. Ascorbic acid synthesis in these cells from old animals was unaffected by various concentrations of tert-butylhydroperoxide, but amounted to only approximately half of the biosynthetic rate when compared to cells from young animals (P<0.001). Cells from young animals were not significantly affected by the tert-butylhydroperoxide treatments. The results demonstrate a declining ability with age to respond to increased oxidative stress. (R)-alpha-Lipoic acid, a mitochondrial coenzyme, is a powerful antioxidant. A two-week dietary supplementation of old animals with 0.5% (R)-alpha-lipoic acid prior to cell isolation almost completely reversed the age-associated effects on ascorbic acid concentration (P<0.0001), recycling (P<0.05) and biosynthesis after oxidative stress. These results provide further evidence for the potential of alpha-lipoic acid in treatment of diseases related to oxidative stress. Furthermore, the study extends the value of ascorbic acid as a biomarker of oxidative stress.

Aging↗
PubMed1975

Automated analysis of vitamin C in pharmaceutical products.

The determination of total vitamin C in the form of both l-ascorbic acid (AA) and dehydroascorbic acid (DHAA) present in pharmaceutical preparations has been automated. Total vitamin C (completely oxidized to DHAA) was determined by reaction with 2,4-dinitrophenylhydrazine while blanks utilized the same reagent after reducing all DHAA to AA. The automated method was applicable to a variety of multivitamin preparations including those containing iron and copper. The mean recovery of L-ascorbic acid added to 11 multivitamin preparations was 99.4% with a coefficient of variation of 2.5%. In the analysis of these products, results obtained by the automated method were essentially the same as those obtained by the original manual method. For preparations containing no copper salts, the results were also comparable to those obtainable by titration with 2,6-dichloroindophenol except in 1 product which contained some DHAA.

Ascorbic Acid↗
PubMed1980

Inhibitory agents and chemical and mechanisms in the dihalomethane-mediated nitrosation of amines with solid nitrite.

Methylene chloride and certain other dihaloalkanes react efficiently with dissolved secondary amines and, in presence of insoluble sodium nitrite, yield N-nitroso compounds. Mechanistic studies indicate that the intermediates in the nitrosation mixture include the formaldiminium ion, the amine hydrochloride and the diaminomethane (aminal). They also indicate that the formaldiminium ion is by far the most reactive toward sodium nitrite, which probably reacts with the former by nucleophilic attack. Ascorbic acid, ascorbyl palmitate, dehydroascorbic acid, potassium iodide and potassium carbonate inhibited the reaction, whereas alpha-tocopherol, Trolox and sodium ascorbate were found to be ineffective. Ascorbic acid reacted with the secondary amine in a complex fashion. The mode of inhibition probably does not involve reduction of the solid nitrite.

Chemical Phenomena↗
PubMed1978

Some studies on ascorbic acid metabolism in hydrazine-treated rats.

The metabolism of ascorbic acid was studied in hydrazine-treated rats. Hydrazine was administered i.p. at a dose of 1.28 mg/day (20% LD50) for each 100 g body weight for 7 days. Hydrazine administration at the present dose did not appear to have an effect on the total ascorbic acid level of liver, kidney, spleen and testis. The adrenal and plasma total ascorbic acid levels were, however, elevated. The activity of liver D-glucuronoreductase and that of liver and kidney dehydroascorbatases were diminished after hydrazine administration. The changes in the activities of liver enzymes were accompanied by a fall in the reduced ascorbic acid level and an elevation in the dehydroascorbic acid level. The uronolactonase activity of liver, on the other hand, remained independent of hydrazine treatment. It has been suggested that hydrazine treatment at the present dose reduced the biosynthesis of L-ascorbic acid from D-glucuronolactone as substrate. In spite of diminished synthesis, the normal level of total ascorbic acid in the liver of hydrazine-treated rats was maintained by reducing the degradation of L-ascorbic acid. The rise in the plasma total ascorbic acid level after hydrazine treatment was ascribed to reduced catabolism and urinary excretion of ascorbic acid, while the elevation in adrenal total ascorbic acid level might result from increased uptake of ascorbic acid by the gland from blood or from nonfunctional accumulation.

Alcohol Oxidoreductases↗
PubMed1999

Redox-dependent and redox-independent subcomponents of protein degradation in perfused myocardium.

The integration of proteolytic pathways with metabolism was investigated in perfused rat myocardium. After a 10-min incorporation period, the minute-to-minute release of [3H]leucine from myocardial proteins was measured in nonrecirculating effluent perfusate. The nontoxic pro-oxidant probe diamide (100 microM) or a supraphysiological concentration of the endogenous oxidative metabolite dehydroascorbic acid (200 microM) reversibly inhibited 75% of myocardial proteolysis consisting of several known subcomponents (redox dependent); however, 25% of proteolysis was diamide insensitive (redox independent). Decrease in extracellular glucose concentration from 10 to 0.1 mM strongly increased the potencies of minimally effective concentrations of diamide (10 microM) or dehydroascorbic acid (15 microM) by approximately 10-fold to the respective potencies maximally inhibiting proteolysis. The reversal of diamide action was also strongly dependent on the perfusate glucose concentration observed at 0.1, 0.2, 1.0 and 10 mM glucose. Proteolytic inhibition caused by diamide (100 microM) was not accompanied by change in basal tissue ATP content of 5 micromol/g wet wt. Conversely, nearly lethal 60% ATP depletion caused by sodium azide (0.4 mM) was not accompanied by change in total [3H]leucine release. Results indicate that a large proteolytic subcomponent (75%) is maintained by redox chains fed by glucose; however, there is no apparent linkage of this proteolysis to short-term ATP fluctuations. A distinct major proteolytic subcomponent (25%) does not vary in response to experimental intervention in either ATP content or redox chains.

Adenosine Triphosphate↗
PubMed1991

Expression of Ascorbic Acid Oxidase in Zucchini Squash (Cucurbita pepo L.).

The expression of ascorbic acid oxidase was studied in zucchini squash (Cucurbita pepo L.), one of the most abundant natural sources of the enzyme. In the developing fruit, specific activity of ascorbic acid oxidase was highest between 4 and 6 days after anthesis. Protein and mRNA levels followed the same trend as enzyme activity. Highest growth rate of the fruit occurred before 6 days after anthesis. Within a given fruit, ascorbic acid oxidase activity and mRNA level were highest in the epidermis, and lowest in the central placental region. In leaf tissue, ascorbic acid oxidase activity was higher in young leaves, and very low in old leaves. Within a given leaf, enzyme activity was highest in the fast-growing region (approximately the lower third of the blade), and lowest in the slow-growing region (near leaf apex). High expression of ascorbic acid oxidase at a stage when rapid growth is occurring (in both fruits and leaves), and localization of the enzyme in the fruit epidermis, where cells are under greatest tension during rapid growth in girth, suggest that ascorbic acid oxidase might be involved in reorganization of the cell wall to allow for expansion. Based on the known chemistry of dehydroascorbic acid, the end product of the ascorbic acid oxidase-catalyzed reaction, we have proposed several hypotheses to explain how dehydroascorbic acid might cause cell wall "loosening."

Journal Article↗
PubMed1979

Stimulation of thiamine diphosphatase activity by ascorbic acid in rat brain microsomes.

The effect of ascorbic acid on microsomal thiamine diphosphatase activity in rat brain was examined. Ascorbic acid at 0.02--0.1 mM increased the thiamine diphosphatase activity by 20--600% and produced a significant amount of lipid peroxide, which was measured with thiobarbiturate under the same conditions as the enzyme. A lag period of about 10 min was observed in the process of stimulation of enzyme activity by ascorbic acid. The stimulation of enzyme activity and the lipid peroxidation induced by ascorbic acid were blocked by metal-binding compounds (EDTA, alpha,alpha'-dipyridyl, o-phenanthroline) and an antioxidant (N,N'-diphenyl p-phenylenediamine). GSH significantly enhanced the stimulation of enzyme activity and formation of lipid peroxide by 0.02--0.05 mM ascorbic acid. The effect of GSH was due in part to maintenance of the concentration of ascorbic acid in the medium, since GSH could convert dehydroascorbic acid, an oxidized form of ascorbic acid, to ascorbic acid.

Animals↗
PubMed2002

Intracellular flavonoids as electron donors for extracellular ferricyanide reduction in human erythrocytes.

Reduction of extracellular ferricyanide [Fe(CN)(6)](-3) to ferrocyanide by intact cells reflects the activity of a trans-plasma membrane oxidoreductase that, in human red blood cells, utilizes ascorbic acid as an electron donor. We herein report that the flavonoids quercetin and myricetin, while inhibiting dehydroascorbic acid uptake-and thus the erythrocyte ascorbic acid content-effectively stimulate the extracellular reduction of ferricyanide. Other flavonoids such as rutin, acacetin, apigenin, and genistein do not show the same effect. The notion that quercetin or myricetin may serve as an intracellular donor for a trans-plasma membrane oxidoreductase is supported by the following lines of evidence: (i) they afford direct reduction of ferricyanide; (ii) extracellular reduction of ferricyanide was not mediated by direct effects of the flavonoids released by the cells and was abolished by the sulphydryl reagent parachloromercuribenzenesulfonic acid (pCMBS); (iii) the intracellular concentrations of quercetin or myricetin well correlate with increases in ferricyanide reduction; (iv) the intracellular concentration of the flavonoids dramatically declines after ferricyanide exposure. Taken together, the results presented in this study demonstrate that myricetin and quercetin, which accumulate in large amounts in red blood cells, act as intracellular substrates of a pCMBS-sensitive trans-plasma membrane oxidoreductase. This may represent a novel mechanism whereby these flavonoids exert beneficial effects under oxidative stress conditions.

4-Chloromercuribenzenesulfonate↗
PubMed1988

Effects of active oxygen scavengers on the peroxidation of linoleic acid catalyzed by dehydro-L-ascorbic acid or its degradation products.

The addition of 1,4-diazabicyclo-[2,2,2]octane (DABCO) (100 mM) or 1,2-dihydroxybenzene-3,5-disulfonic acid (Tiron) (1 mM) to a reaction mixture containing 10 mM linoleic acid (LA), 20% EtOH, and 135 microM dehydroascorbic acid (DHA) as a catalyst suppressed LA peroxidation, but the addition of mannitol (approximately 100 mM), uric acid (100 microM), and catalase (6.5 units) did not. DHA or 2,3-diketo-L-gulonic acid (DKG) accelerated LA peroxidation, but the splitting products of DHA did not affect LA peroxidation. These results suggest that some specific radicals are liberated in the degradation of DHA or DKG.

1,2-Dihydroxybenzene-3,5-Disulfonic Acid Disodium ↗
PubMed2004

Breath condensate hydrogen peroxide correlates with both airway cytology and epithelial lining fluid ascorbic acid concentration in the horse.

The relationship between hydrogen peroxide (H2O2) concentration in expired breath condensate (EBC) and cytology of the respiratory tract obtained from tracheal wash (TW) or bronchoalveolar lavage (BAL), and epithelial lining fluid (ELF) antioxidant status is unknown. To examine this we analysed the concentration of H2O2 in breath condensate from healthy horses and horses affected by recurrent airway obstruction (RAO), a condition considered to be an animal model of human asthma. The degree of airway inflammation was determined by assessing TW inflammation as mucus, cell density and neutrophil scores, and by BAL cytology. ELF antioxidant status was determined by measurement of ascorbic acid, dehydroascorbate, reduced and oxidised glutathione, uric acid and alpha-tocopherol concentrations. RAO-affected horses with marked airway inflammation had significantly higher concentrations of breath condensate H2O2 than control horses and RAO-affected horses in the absence of inflammation (2.0 +/- 0.5 micromol/l. 0.4 +/- 0.2 micromol/l and 0.9 +/- 0.2 micromol/l H2O2, respectively; p < 0.0001). The concentration of breath condensate H2O2 was related inversely to the concentration of ascorbic acid in ELF (r = -0.80; p < 0.0001) and correlated positively with TW inflammation score (r = 0.76, p < 0.0001) and BAL neutrophil count (r = 0.80, p < 0.0001). We conclude that the concentration of H2O2 in breath condensate influences the ELF ascorbic acid concentration and provides a non-invasive diagnostic indicator of the severity of neutrophilic airway inflammation.

Airway Obstruction↗
PubMed1998

Oxidation products of uric acid and ascorbic acid in preterm infants with chronic lung disease.

Allantoin, the oxidation product of uric acid (UA), can be used as an in vivo marker of free radical generation. The aims of the present study were to evaluate the allantoin changes in plasma and bronchoalveolar lavage fluid (BALF) as well as to examine plasma levels of ascorbic acid (AA) and its oxidation product, dehydroascorbic acid (DHAA), in infants with or without chronic lung disease (CLD) during the first week of life. The study population was 20 infants of 24-30 weeks gestation, comprising 10 who subsequently developed CLD and 10 without CLD. In the CLD infants, the plasma allantoin/UA ratio showed a significant increase after day 1 and continued to increase gradually to reach a peak on day 6 (6.5 +/- 4.1% for CLD and 2.1 +/- 0.9% for non-CLD infants). The allantoin/UA ratio in BALF was also higher in CLD infants and the difference reached significance on days 4-6 (41.2 +/- 15.8% for CLD and 11.7 +/- 9.9% for non-CLD infants). In contrast to allantoin, the plasma DHAA/AA ratio did not differ between the 2 groups throughout the study period. Our findings that the allantoin/UA ratios were significantly higher in CLD than non-CLD infants not only in plasma but also in BALF, and that the intergroup differences of this ratio in both plasma and BALF was more prominent in the latter half of the first week of life further confirm our previous speculation that oxygen radicals are involved in the development of neonatal CLD.

Allantoin↗