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DNA methylation is a heritable epigenetic modification involved in gene silencing, imprinting, and the suppression of retrotransposons (1). Global DNA demethylation occurs in the early embryo and the germ line (2,3), and may be mediated by Tet (ten eleven translocation) enzymes (4-6), which convert 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC) (7). Tet enzymes have been studied extensively in mouse embryonic stem (ES) cells (8-12), which are generally cultured in the absence of vitamin C, a potential cofactor for Fe(II)2-oxoglutarate dioxygenase enzymes such as Tet enzymes. Here we report that addition of vitamin C to mouse ES cells promotes Tet activity, leading to a rapid and global increase in 5hmC. This is followed by DNA demethylation of many gene promoters and upregulation of demethylated germline genes. Tet1 binding is enriched near the transcription start site of genes affected by vitamin C treatment. importantly, vitamin C, but not other antioxidants, enhances the activity of recombinant Tet1 in a biochemical assay, and the vitamin-C-induced changes in 5hmC and 5mC are entirely suppressed in Tet1 and Tet2 double knockout ES cells. Vitamin C has a stronger effect on regions that gain methylation in cultured ES cells compared to blastocysts, and in vivo are methylated only after implantation. in contrast, imprinted regions and intracisternal A particle retroelements, which are resistant to demethylation in the early embryo (2,13), are resistant to vitamin-C-induced DNA demethylation. Collectively, the results of this study establish vitamin C as a direct regulator of Tet activity and DNA methylation fidelity in ES cells., ES cells are derived from the inner cell mass (ICM) of the blastocyst and can be cultured in vitro to maintain a pluripotent state. Media composition has been shown previously [...]

Ascorbic acid (AA), one of the principal micronutrients in horticultural crops, plays a key role in the human metabolism, and its determination in food products has a great significance. Citrus fruits are rich in AA, but its content is highly susceptible to change during postharvest processing and storage. We present a new ultralow-cost system, constituted of an amperometric microsensor composed of three rod carbon electrodes connected to a telemetric device, for online detection of AA in orange juice, as an alternative to conventional analytical methods. The in vitro calibration, ranged from 0 to 5 mM, and AA juice content was calculated by adding low volumes of sample into an acetate buffer solution at a constant potential of +120 mV vs carbon pseudoreference. This new approach, which is simple, expandable, and inexpensive, seems appropriate for large scale commercial use. 10.1021/ac100303p

Problem statement: In an effort to increase growth, improve feed utilization, reduce stress and prevent certain diseases, a 14 week feeding trial was conducted to determine the effects of different levels of dietary vitamin C (ascorbic acid) on growth, feed utilization and hematological changes in Clarias gariepinus fingerlings. Approach: Diets were formulated to contain 0, 50, 100, 150, 500, 1000 and 1500 mg L-ascorbic acid [kg.sup.-1] of feed contributing 0, 0.05, 0.10, 0.15, 0.5, 1.0 and 1.5% to the formulated diets respectively. Fish of mean weight 10.12[+ or -]0.7 g were fed on experimental diets in triplicate groups. Weight gain of fish fed diet with 0% of vitamin C were significantly (p0.05) differences in weight gain among the fish fed diets containing 0.05, 0.10 and 0.15% of vitamin C. Generally, fish fed vitamin C supplemented diets showed better growth rate, feed conversion ratio and protein efficiency compared with those without vitamin C supplementation. Results: The results of hematological analyses of fish showed that red blood cell, white blood cell, haemoglobin concentration and packed cell volume were not significantly (p>0.05) affected by vitamin C supplemented diets. Fish fed the vitamin C-free diet begin to show deficiency signs such as erratic swimming, flashing, skin darkening and reduced growth at 12 weeks of feeding trial. Conclusion: This study indicated that 50 mg [kg.sup.-1] of ascorbic acid is sufficient to prevent C. gariepinus fingerlings from developing clinical symptoms relating to vitamin C deficiency. A mega dose of 1500 mg [kg.sup.-1] of ascorbic acid gave maximum growth performance and feed utilization efficiency. Key words: Vitamin C, growth, feed utilization, haematology, Clarias gariepinus, INTRODUCTION The African catfish, Clarias gariepinus is the most popular and widely cultivated fish in Nigeria (1). The fingerlings are produced in over 70% of the functional hatcheries in the [...]

A highly selective receptor for serotonin was designed using cages formed by the (R)-lipo-diaza-18-crown-6 self-assembled monolayer (SAM) on gold and experimentally verified by a variety of electrochemical experiments in solutions containing large amounts of dopamine and ascorbic acid, as well as other interferents. The molecular modeling study showed that parameters such as the H-[pi] interaction provided important driving forces for the cage to form a strong inclusion complex with serotonin. The charge-transfer resistance ([R.sub.CT]'s) to/from redox probe ions, Fe[(CN).sub.6.sup.3-/4-], was greatly enhanced because of their electrostatic attractions to ammonium ions of serotonin molecules captured by cages. The changes in [R.sub.CT]-values were shown to be remarkably selective for serotonin in the presence of many interferents.

Higher plant species differ widely in their growth responses to ammonium (N[H.sup.+.sub.4]). However, the molecular genetic mechanisms underlying N[H.sup.+.sub.4] sensitivity in plants remain unknown. Here, we report that mutations in the Arabidopsis gene encoding GDP-mannose pyrophosphorylase (GMPase) essential for synthesizing GDP-mannose confer hypersensitivity to N[H.sup.+.sub.4]. The in planta activities of WT and mutant GMPases all were inhibited by N[H.sup.+.sub.4], but the magnitude of the inhibition was significantly larger in the mutant. Despite the involvement of GDP-mannose in both L-ascorbic acid (AsA) and N-glycoprotein biosynthesis, defective protein glycosylation in the roots, rather than decreased AsA content, was linked to the hypersensitivity of GMPase mutants to N[H.sup.+.sub.4]. We conclude that N[H.sup.+.sub.4] inhibits GMPase activity and that the level of GMPase activity regulates Arabidopsis sensitivity to N[H.sup.+.sub.4]. Further analysis showed that defective N-glycosylation of proteins, unfolded protein response, and cell death in the roots are likely important downstream molecular events involved in the growth inhibition of Arabidopsis by N[H.sup.+.sub.4]. glycosylation | N[H.sup.+.sub.4] toxicity | unfolded protein response | L-ascorbic acid

The ability of the technique of large-amplitude Fourier transformed (FT) ac voltammetry to facilitate the quantitative evaluation of electrode processes involving electron transfer and catalytically coupled chemical reactions has been evaluated. Predictions derived on the basis of detailed simulations imply that the rate of electron transfer is crucial, as confirmed by studies on the ferrocenemethanol (FcMeOH)-mediated electrocatalytic oxidation of ascorbic acid. Thus, at glassy carbon, gold, and boron-doped diamond electrodes, the introduction of the coupled electrocatalytic reaction, while producing significantly enhanced dc currents, does not affect the ac harmonics. This outcome is as expected if the [FcMeOH.sup.o/+] process remains fully reversible in the presence of ascorbic acid. In contrast, the ac harmonic components available from FT-ac voltammetry are predicted to be highly sensitive to the homogeneous kinetics when an electrocatalytic reaction is coupled to a quasi-reversible electron-transfer process. The required quasi-reversible scenario is available at an indium tin oxide electrode. Consequently, reversible potential, heterogeneous charge-transfer rate constant, and charge-transfer coefficient values of 0.19 V vs Ag/AgCl, 0.006 cm [s.sup.-1] and 0.55, respectively, along with a second-order homogeneous chemical rate constant of 2500 [M.sup.-1] [s.sup.-1] for the rate-determining step in the catalytic reaction were determined by comparison of simulated responses and experimental voltammograms derived from the dc and first to fourth ac harmonic components generated at an indium fin oxide electrode. The theoretical concepts derived for large-amplitude FT ac voltammetry are believed to be applicable to a wide range of important solution-based mediated electrocatalytic reactions.

The anaerobic utilization of L-ascorbate by gene products of the ula regulon in Escherichia coil has been widely documented. Under aerobic conditions, we have shown that this metabolism is only functional in the presence of casein acid hydrolysate. Transcriptional fusions and proteomic analysis indicated that both the ula regulon and the yiaK-S operon are required for the aerobic utilization of this compound. The aerobic dissimilation of L-ascorbate shares the function of three paralogous proteins, UlaD/YiaQ, UlaE/YiaR and UlaF/YiaS, which encode a decarboxylase, a 3-epimerase and a 4-epimerase, respectively. In contrast, L-ascorbate enters the cells through the ula-encoded phosphotransferase transport system, but it is not carried by the yiaMNO-encoded ABC transporter. Proteomic analysis also indicated enhanced expression of the alkyl hydroperoxide reductase encoded by the ahpC gene, suggesting a response to oxidative stress generated during the aerobic metabolism of L-ascorbate. Control of ahpC expression by the OxyR global regulator in response to L-ascorbate concentration is consistent with the formation of hydrogen peroxide under our experimental conditions. The presence of certain amino acids such as proline, threonine or glutamine in the culture medium allowed aerobic L-ascorbate utilization by Escherichia coil cells. This effect could be explained by the ability of these amino acids to allow yiaK-S operon induction by L-ascorbate, thus increasing the metabolic flux of L-ascorbate dissimilation. Alternatively, these amino acids may slow the rate of L-ascorbate oxidation.

The mouse has become the most important model organism for the study of human physiology and disease. However, until the recent generation of mice lacking the enzyme gulanolactone oxidase (Gulo), the final enzyme in the astorbic acid biosynthesis pathway, examination of the role of ascorbic acid in various biochemical processes using this model organism has not been possible. In the mouse, similar to most mammals but unlike humans who carry a mutant copy of this gene, Gulo produces ascorbic acid from glucose. We report here that, although ascorbic acid is essential for survival, its absence does not lead to measurable changes in proline hydroxylation. Vitamin C deficiency had no significant effect on the hydroxylation of proline and collagen production during tumor growth or in angiogenesis associated with minor or mammary gland growth. This suggests that factors other than ascorbic acid can support proline hydroxylation and collagen synthesis in vivo. Furthermore, the failure of [Gulo.sup-/-] mice to thrive on a vitamin C-deficient diet therefore suggests that ascorbic acid plays a critical role in survival other than the maintenance of the vasculature. ascorbic acid; collagen: angiogenesis: prolyl hydroxylase

The biosynthetic pathway of L-tartaric acid, the form most commonly encountered in nature, and its catabolic ties to vitamin C, remain a challenge to plant scientists. Vitamin C and L-tartaric acid are plant-derived metabolites with intrinsic human value. In contrast to most fruits during development, grapes accumulate L-tartaric acid, which remains within the berry throughout ripening. Berry taste and the organoleptic properties and aging potential of wines are intimately linked to levels of L-tartaric acid present in the fruit, and those added during vinification. Elucidation of the reactions relating L-tartaric acid to vitamin C catabolism in the Vitaceae showed that they proceed via the oxidation of L-idonic acid, the proposed rate-limiting step in the pathway. Here we report the use of transcript and metabolite profiling to identify candidate cDNAs from genes expressed at developmental times and in tissues appropriate for L-tartaric acid biosynthesis in grape berries. Enzymological analyses of one candidate confirmed its activity in the proposed rate-limiting step of the direct pathway from vitamin C to tartaric acid in higher plants. Surveying organic acid content in Vitis and related genera, we have identified a non-tartrate-forming species in which this gene is deleted. This species accumulates in excess of three times the levels of vitamin C than comparably ripe berries of tartrate-accumulating species, suggesting that modulation of tartaric acid biosynthesis may provide a rational basis for the production of grapes rich in vitamin C. idonate dehydrogenase | transcriptional profiling | organic acid | biosynthesis | Vitis vinifera