Oleic Acid Inhibits Gap Junction Permeability and Increases Glucose Uptake in Cultured Rat Astrocytes

Abstract: The role of oleic acid in the modulation of gap junction permeability was studied in cultured rat astrocytes by the scrape-loading/Lucifer yellow transfer technique. Incubation with oleic acid caused a dose-dependent inhibition of gap junction permeability by 79.5% at 50 µ M , and no further inhibition was observed by increasing the oleic acid concentration to 100 µ M . The oleic acid-mediated inhibition of gap junction permeability was reversible and was prevented by bovine serum albumin. The potency of oleic acid-related compounds in inhibiting gap junction permeability was arachidonic acid > oleic acid > oleyl alcohol > palmitoleic acid > stearic acid > octanol > caprylic acid > palmitic acid > methyloleyl ester. Oleic acid and arachidonic acid, but not methyloleyl ester, increased glucose uptake by astrocytes. Neither oleic acid nor arachidonic acid increased glucose uptake in the poorly coupled glioma C6 cells. These results support that the inhibition of gap junction permeability is associated with the increase in glucose uptake. We suggest that oleic acid may be a physiological mediator of the transduction pathway leading to the inhibition of intercellular communication.     

Photocontrol of chlorogenic acid biosynthesis in potato tuber discs

The appearance of phenylalanine ammonia-lyase activity and the accumulation of chlorogenic acid in potato tuber discs are stimulated by illumination with white light, whereas the appearance of cinnamic acid 4-hydroxylase activity is unaffected by illumination. The photosensitive step in chlorogenic acid biosynthesis may be by-passed by treatment of discs with exogenous supplies of cinnamic acid, whereas treatment of discs with phenylalanine does not isolate the photosensitive step. Therefore, the site of photocontrol of chlorogenic acid biosynthesis in potato tuber discs is the reaction catalysed by phenylalanine ammonia-lyase. Cinnamic acid 4-hydroxylase activity in vitro is unaffected by p-coumaric acid, caffeic acid or chlorogenic acid. Phenylalanine ammonia-lyase activity in vitro is sensitive to inhibition by cinnamic acid. The in vitro properties of the two enzymes are also consistent with the hypothesis that phenylalanine ammonia-lyase rather than cinnamic acid 4-hydroxylase is important in the regulation of chlorogenic acid biosynthesis in potato tuber discs.     

酚酸类物质对三七幼苗的化感影响

该文研究了不同浓度的阿魏酸、对香豆酸、丁香酸、对羟基苯甲酸、香草酸5种酚酸类物质对三七幼苗生长和生理的影响。结果表明:处理后,三七幼苗的苗高、根长、可溶性蛋白质含量、根系活力、CAT以及POD活性均有所降低。其中,阿魏酸各处理组幼苗的苗高及POD活性均显著降低,50、100 mg·L~(-1)的对香豆酸以及100 mg·L~(-1)的香草酸处理组幼苗苗高也分别比对照显著降低16.19%、16.67%和29.29%;对香豆酸、丁香酸以及对羟基苯甲酸各处理组幼苗根长均显著低于对照;香草酸处理组幼苗的根系活力也显著低于对照,且幼苗的CAT活性在10、50、100 mg·L~(-1)丁香酸、对羟基苯甲酸以及香草酸处理下也达到了显著降低水平。此外,1 mg·L~(-1)阿魏酸以及100 mg·L~(-1)香草酸处理组幼苗的叶绿素含量也均显著降低;中高浓度的阿魏酸、对香豆酸、丁香酸、对羟基苯甲酸增加了三七幼苗的MDA含量,而香草酸在0.1、1、10、100 mg·L~(-1)浓度下显著降低幼苗的MDA含量;丁香酸、香草酸、对羟基苯甲酸以及中高浓度的对香豆酸增加了三七幼苗的SOD活性,且香草酸各处理组均达到了显著性水平。综上结果表明,5种酚酸类物质对三七幼苗均具有一定的化感抑制作用,但各酚酸物质的作用方式及强度并不完全一致,阿魏酸的化感影响较大,这为进一步研究三七的化感自毒作用提供了一定的理论参考。     

The preparation and microbiological evaluation of the inhibitory effects of some acrylic acid derivatives

The following acrylic acid derivatives have been prepared and microbiologically evaluated as possible inhibitors of the growth of lactobacilli; indoleacrylic acid, β-(2-quinolyl)-, β-(3-quinolyl)-, β-(4-quinolyl) acrylic acids, cinnamic acid, p-hydroxycinnamic acid, p-dimethylaminocinnamic acid, p-diethylaminocinnamic acid, thienylacrylic acid, furylacrylic acid, and α-ethylacrylic acid.The utilization of tryptophan by Leuconostoc mesenteroides P-60 and Lactobacillus arabinosus was inhibited by the isomeric quinolylacrylic acid derivatives as well as by indoleacrylic acid. With this latter compound and the β-(3-quinolyl)acrylic acid, competitive inhibition was shown.p-Hydroxycinnamic acid inhibited the utilization of phenylalanine and tyrosine by all the organisms tested. At similar concentrations neither cinnamic acid nor phenol exerted any inhibitory effect.The effects of all inhibitors could be at least partially reversed by the addition of larger quantities of the corresponding amino acids.     

Application of melatonin and PGPR alleviates thiamethoxam induced toxicity by regulating the TCA cycle in Brassica juncea L

Thiamethoxam, a broad spectrum, neonicotinoid insecticide, is used on various crops including Brassica juncea L. to protect from intruding insects such as leaf-hoppers, aphids, thrips and white-flies. Exposure to thiamethoxam causes acute malady such as tumour development, cell apoptosis, liver damage and neurotoxicity. Melatonin is entailed in umpteen developmental processes of plants, including stress responses. The pleiotropic effects of melatonin in modulating plant growth validate it’s imperative contribution as multi-regulatory substance. Exiguous information is known about the role of Pseudomonas putida in improving plant growth under thiamethoxam stress. Taking these aspects into consideration the contemporary study investigates the role of melatonin and Pseudomonas putida strain MTCC 3315 in alleviating the thiamethoxam induced toxicity in B. juncea plant. Fourier Transform Infrared Spectroscopy (FTIR) analysis uncloaked that thiamethoxam induced stress primarily affects the protein content of plant as compared to lipids, carbohydrates and cell wall components. Organic acid profiling of the treated samples carried-out by High-Performance Liquid Chromatography (HPLC), reported an upregulation in the level of organic acids, malic acid (110%), citric acid (170%), succinic acid (81%), fumaric acid (40%) and ascorbic acid (55%) in thiamethoxam treated plants compared to the investigational untreated plants. The melatonin treated seedlings grown under thiamethoxam stress, exhibit increased level of malic acid, citric acid, succinic acid, fumaric acid and ascorbic acid by 81%, 0.94%, 11%, 21% and 6% respectively. Further, thiamethoxam stressed plants inoculated with Pseudomonas putida showed stupendous up-regulation by 161% (malic acid), by 14% (citric acid), by 33% (succinic acid), by 30% (fumaric acid), by 100% (oxalic acid) respectively. Lastly, the combinatorial application of melatonin and Pseudomonas putida resulted in prodigious upsurge of malic acid by 165%, succinic acid by 69%, fumaric acid by 42% respectively in contrast to distinct melatonin and Pseudomonas putida treatments. The accumulation of organic acids ascertains the defence against thiamethoxam stress and corresponds to meet the energy generation requirement to skirmish thiamethoxam mediated abiotic stress in Brassica juncea plant.     

Anaerobic Naphthalene Degradation by a Sulfate-Reducing Enrichment Culture

Anaerobic naphthalene degradation by a sulfate-reducing enrichment culture was studied by substrate utilization tests and identification of metabolites by gas chromatography-mass spectrometry. In substrate utilization tests, the culture was able to oxidize naphthalene, 2-methylnaphthalene, 1- and 2-naphthoic acids, phenylacetic acid, benzoic acid, cyclohexanecarboxylic acid, and cyclohex-1-ene-carboxylic acid with sulfate as the electron acceptor. Neither hydroxylated 1- or 2-naphthoic acid derivatives and 1- or 2-naphthol nor the monoaromatic compounds ortho-phthalic acid, 2-carboxy-1-phenylacetic acid, and salicylic acid were utilized by the culture within 100 days. 2-Naphthoic acid accumulated in all naphthalene-grown cultures. Reduced 2-naphthoic acid derivatives could be identified by comparison of mass spectra and coelution with commercial reference compounds such as 1,2,3,4-tetrahydro-2-naphthoic acid and chemically synthesized decahydro-2-naphthoic acid. 5,6,7,8-Tetrahydro-2-naphthoic acid and octahydro-2-naphthoic acid were tentatively identified by their mass spectra. The metabolites identified suggest a stepwise reduction of the aromatic ring system before ring cleavage. In degradation experiments with [1-¹³C]naphthalene or deuterated D₈-naphthalene, all metabolites mentioned derived from the introduced labeled naphthalene. When a [¹³C]bicarbonate-buffered growth medium was used in conjunction with unlabeled naphthalene, ¹³C incorporation into the carboxylic group of 2-naphthoic acid was shown, indicating that activation of naphthalene by carboxylation was the initial degradation step. No ring fission products were identified.     

Studies on the Metabolism of Gallic Acid by Microorganisms

The intermediary metabolism of gallic acid by Aspergillus niger under the influence of some added inhibitors has been studied. The decomposition of gallic acid by lyophilized cells under fluoroacetate inhibition allowed cis-aconitic acid, α-ketoglutaric acid and citric acid to accumulate. A mechanism of gallic acid decomposition via cis-aconitic acid has been inferred.     

A method for the degradation of radioactive nicotinic acid

A chemical degradation scheme is reported, which permits the measurement of the radioactivity of each carbon atom of nicotinic acid. Nicotinic acid is decarboxylated by heating with copper chromite to give carbon dioxide (C-7) and pyridine. The pyridine is converted into 4-nitropyridine 1-oxide, which is heated with aqueous calcium hypobromite to give tribromonitromethane. Combustion of the latter gives carbon dioxide derived from C-4 of the nicotinic acid. Nicotinic acid is also reduced to nipecotic acid, which is oxidized to succinic acid by acidic potassium permanganate. Stepwise degradation of the succinic acid by standard procedures gives two samples of carbon dioxide, which correspond to C-3, C-6 and C-4, C-5 of the nicotinic acid. Benzoylation of the nipecotic acid, followed by oxidation with permanganate at pH7, gives 5-amino-4-carboxyvaleric acid; this is converted into 2-methyleneglutaric acid by the action of nitrous acid. Hydrogenation of the 2-methyleneglutaric acid over rhodium in methanol gives 2-methylglutaric acid, which is oxidized with dilute chromic acid to acetic acid. Stepwise degradation of the acetic acid by standard procedures gives two samples of carbon dioxide, which correspond to C-2 and C-3 of the nicotinic acid. Thus the radioactivities of C-2, C-3, C-4 and C-7 are determined directly and those of C-5 and C-6 by difference. The method was shown to be isotopically valid for [2,3,7-¹⁴C]-, [4,6-¹⁴C₂]- and [5-¹⁴C]-nicotinic acid.     

酸沉降对森林生态系统影响的研究现状及展望

酸沉降影响下物质循环及其不平衡研究;酸沉降对土壤理化性质的影响;森林水化学方面的研究;酸沉降下重金属的活化研究;酸沉降对植物生长的影响研究;酸沉降和气候变化对森林的影响;模拟酸雨对土壤理化性质和植物生长的影响;酸沉降下土壤风化问题的研究;运用模型对酸化问题的研究;森林土壤人为和自然的酸化;酸沉降临界负荷的研究;酸沉降和其它污染物对植物的联合影响;酸化土壤恢复研究等方面介绍了酸沉降对森林生态系统影响的研究现状,并阐明了今后研究的方向及应该注意的问题。     

Inhibition of hepatic gluconeogenesis and lipogenesis by benzoic acid,p-tert.-butylbenzoic acid,and a structurally related hypolipidemic agent SC-33459

Benzoic acid, p-tert.-butylbenzoic acid, and a structurally related hypolipidemic agent SC-33459 were found to inhibit glucose synthesis by hepatocytes isolated from 48-h fasted rats as well as fatty acid synthesis by hepatocytes isolated from meal-fed rats. Glucose synthesis was less sensitive than fatty acid synthesis. Benzoic acid was the least effective inhibitor of both processes; SC-33459 and p-tert.-butylbenzoic acid were very potent inhibitors with similar efficacy. Glycine prevented the inhibition of fatty acid synthesis caused by benzoic acid, but had no effect on that caused by p-tert.-butylbenzoic acid. Octanoate opposed the inhibitory effects of both benzoic acid and p-tert.-butylbenzoic acid. Oxidation of [1-¹⁴C]oleate to ketone bodies and acid-soluble radioactive products was inhibited by both p-tert.-butylbenzoic acid and SC-33459. Preincubation of hepatocytes with SC-33459 was required for the latter effect, suggesting catabolism of this compound may be involved. SC-33459 is a p-tert.-butylphenyl derivative which should be readily converted to p-tert.-butylbenzoic acid by β oxidation. Both p-tert.-butylbenzoic acid and SC-33459 decreased citrate levels dramatically. All three compounds reduced CoA and acetyl-CoA levels and increased medium-chain acyl-CoA ester levels. p-tert.-Butylbenzoic acid and SC-33459 also increased long-chain acyl-CoA ester levels. The increase in medium-chain acyl-CoA levels presumably reflects benzoyl-CoA formation from benzoic acid and p-tert.-butylbenzoyl-CoA formation from p-tert.-butylbenzoic acid and SC-33459. Inhibition of glucose and fatty acid synthesis by these compounds may be due to effects on specific enzymes or to CoA sequestration.     

Effect of calcium on synthesis of dipicolinic acid inPenicillium citreoviride and its feedback resistant mutant

Dipicolinic acid synthesis inPenicillium citreoviride strain 3114 was inhibited by Ca²⁺ ions, but not by Ba²⁺, Cu²⁺or Fe²⁺. Among the metals tested, only Zn²⁺ inhibited the synthesis of dipicolinic acid and promoted sporulation. None of these metals reversed the inhibition by Ca²⁺ or Zn²⁺. A mutant 27133-dpa-ca selected for resistance to feedback inhibition by dipicolinic acid: Ca²⁺ complex showed cross-resistance to inhibition by dipicolinic acid: Zn²⁺. Both 3114 and271 33-dpa-ca excreted a number of aliphatic and amino acids during secondary metabolism of dipicolinic acid. In the presence of 1000 ppm of Ca²⁺, accumulation of citric acid and α-aminoadipic acid was completely inhibited under conditions of inhibition of dipicolinic acid in parent strain 3114 but not in the mutant. Citric acid with or without Ca²⁺ did not inhibit thede novo synthesis of dipicolinic acid in the strain 3114. In fact, citric acid in the presence of Ca²⁺ improved significantly rate of dipicolinic acid synthesis. Apart from resistance to feed back inhibition by dipicolinic acid: Ca²⁺ complex, mutant differed from the parent in three other aspectsviz. (i) dipicolinic acid synthesis was not subject to catabolite repression by glucose, (ii) sporulation as well as dipicolinic acid synthesis was dependent on the presence of Ca²⁺ ions in the medium and (iii) Mg²⁺ requirement for the mutant increased three fold. Higher requirement of the Mg²⁺ could be partially relieved by Ca²⁺ during secondary metabolism. The results support the inference thatde novo synthesis of dipicolinic acid is regulated through feedback inhibition by dipicolinic acid: Ca²⁺complex.     

Sugar determination in ulvans by a chemical-enzymatic method coupled to high performance anion exchange chromatography

The sugar determination of ulvans, the water-soluble polysaccharides from Ulva sp. and Enteromorpha sp., was optimized by combining partial acid prehydrolysis (2 mol L-1 trifluoroacetic acid, 120°C) with enzymic hydrolysis (with β-D-glucuronidase). The different constitutive sugars (rhamnose, galactose, glucose, xylose, glucuronic acid), released after hydrolysis, were separated by high performance anion-exchange chromatography and determined by pulsed amperometric detection. The ulvanobiouronic acid, β-D-GlcA-(1,4)-L-Rha, which is the main constituent of ulvans was always present after 3 h of trifluoroacetic acid hydrolysis (approx. 2% D.M.) when acid hydrolysis was performed alone but the xylose amount fell to 75% of its maximum value at this time. The optimal duration of 2 mol L⁻¹ trifluoroacetic acid hydrolysis of ulvans (i.e. without any degradation of xylose, rhamnose and glucuronic acid) was 45 min. Additionnal treatment of the partial acid hydrolysate by purified β-D-glucuronidase allowed the hydrolysis of the residual ulvanobiouronic acid in rhamnose and glucuronic acid. High performance anion exchange chromatography coupled to this chemical-enzymic hydrolysis revealed to be a high resolution chromatographic technique for monitoring the hydrolysis of the aldobiouronic acid by β-D-glucuronidase. This method allowed the simultaneous quantitative determination of neutral and acidic sugars and revealed the presence of iduronic acid inulvans. This revised version was published online in September 2006 with corrections to the Cover Date.     

Microbial transformation of isonicotinic acid hydrazide and isonicotinic acid bySarcina sp

Metabolism of isonicotinic acid and isoniazid bySarcina sp. led to the formation of two metabolites which were characterised as 2-hydroxyisonicotinic acid and citrazinic acid. The blue pigment formed during fermentation was shown to be derived from the auto-oxidation of citrazinic acid. 2-Oxo-glutarate accumulated as the major keto acid when isonicotinic acid or isonicotinic acid hydrazide metabolism was inhibited by 1 mM sodium arsenite. Isonicotinic acid, 2-hydroxy-isonicotinic acid and 2-oxo-glutarate were oxidised by isonicotinic acid hydrazide or isonicotinic acid-grown cells; citrazinic acid was, however, not oxidised. Isoniazid hydrazine hydrolase, isonicotinic acid and 2-hydroxyisonicotinic acid hydroxylases were detected in the cell-free extract ofSarcina sp. grown on isonicotinic acid hydrazide or isonicotinic acid. Communication no. 2427from Central Drug Research Institute, Lucknow.     

l-Glutamic Acid Fermentation

A study was made on the differences between Brevibacterium thiogenitalis No. 653 and its oleic acid-requiring mutant D-248 in some physiological characteristics.

The most important difference of the characteristics was found in their intracellular fatty acid contents. Namely, the cellular oleic acid content of D-248 was scarcely affected by biotin but limited by the oleic acid which was added to the medium.

On the other hand, various enzyme activities and rates of oxygen uptake for several organic acids were found to be slightly different between the two strains.

These observations suggest that oleic acid has an important role for the production of l-glutamic acid.

The effect of biotin and oleic acid on the cellular fatty acid contents, and the relation between the cellular fatty acid contents and the productivity of l-glutamic acid were investigated using Brevibacterium thiogenitalis No. 653 and its oleic acid-requiring mutant, D-248.

While the synthesis of palmitic acid in D-248 was stimulated by biotin and competitively reversed by oleic acid added to the culture medium, the level of cellular oleic acid was scarcely affected by biotin but regulated by oleic acid in the medium.

For the productivity of L-glutamic acid, the most important factor was the level of cellular oleic acid, and the effect of cellular palmitic acid was considerably weak. This relation was subjected to a figuration and able to be expressed on the whole as one exponential-like curve. An amount of over 70 per cent of cellular fatty acids was distributed in the phospholipid fraction and its fatty acid composition was almost the same as that of whole cells.     

Fatty Acid Metabolism in Microorganisms

During the investigation on the metabolism of azelaic acid by Micrococcus sp., it was found that the bacterium produced a large amount of keto acid (α-ketoglutaric acid) under the restricted condition for nitrogen source. The acid was identified as α-ketoglutaric acid by physico-chemical and biological methods. The mechanism of the production of α-ketoglutaric acid from azelaic acid was investigated. From the result, it was suggested that α-ketoglutaric acid production proceeded thrpugh the further oxidation of acetic acid produced from azelaic acid and that the production might be functioned by TCA cycle enzymes of the bacterium. Similarly, α-ketoglutaric acid was found to be produced remarkably from other various fatty acids.     

Studies on the Hypertrophic Disease of Cherry (Genus Prunus), So-called “Witch’s Broom” Caused by Taphrina wiesneri

Metabolites of Taphrina wiesneri (Rath.) Mix. were examined. Brassicasterol, stearic acid, and p-hydroxyphenylacetic acid were isolated in crystalline form. p-Hydroxybenzoic acid and vanillic acid were identified by paper chromatography and UV measurement. Palmitic acid was identified by gas-chromatography. The fungus produced usually these compounds on any one of four kinds of medium used. p-Hydroxyphenylacetic acid promoted germination of rape seeds at the concentration of 20 ppm in water and showed inhibition at 250 ppm.

Phenolic acids and their related compounds in Japanese flowering cherry leaves infected by Taphrina wiesneri were examined. In the acidic and neutral extracts of infected cherry leaves (I), eighteen compounds positive to diazotized sulfanilic acid and two fluorescent compounds were detected by paper chromatography. Of these compounds, coumarin, 3, 4-dihydrocoumarin, melilotic acid, o- and p-coumaric acids, p-hydroxybenzoic melilotic acid, ferulic acid and caffeic acid were identified. Melilotic acid and coumarin were obtained in crystalline form. The amount of melilotic acid in I was higher than that in healthy leaves independent of sample source, although increased with the growth of cherry leaves.     

Stimulation of thiamine diphosphate activity by ascorbic acid in rat brain microsomes

The effect of ascorbic acid on microsomal thiamine diphosphate activity in rat brain was examined. Ascorbic acid at 0.02–0.1 mM increased the thiamine diphosphate 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, α,α′-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.     

Metabolism of Aromatic Compounds by Microbes

The metabolic products of m-hydroxybenzoic acid formed by certain Pseudomonas, Micrococcus, and Bacterium strains which possess oxidizing ability of this acid were detected by paperchromatography. It was recognized that protocatechuic acid or gentisic acid are intermediary metabolites of m-hydroxybenzoic acid by these bacteria and the both acids are not detected in one cultural broth.     

Influence of lignin-derived phenolic compounds on the Clostridium thermocellum endo-β-1,4-xylanase XynA

Phenolic compounds released during pretreatment of lignocellulosic biomass influence its enzymatic hydrolysis. To understand the effects of these compounds on the kinetic properties of xylan-degrading enzymes, the present study employed the recombinant cellulosomal endo-β-1,4-xylanase, thermostable GH11 XynA protein from Clostridium thermocellum, as an enzyme model to evaluate the effects of 4-hydroxybenzoic acid, gallic acid, vanillin, tannic acid, p-coumaric acid, ferulic acid, syringaldehyde, and cinnamic acid. XynA was deactivated by the assayed phenols at 60 °C, presenting the strongest deactivation in the presence of tannic acid, with an activity reduction of about 80 %. Thermal stability of XynA was influenced by ferulic acid, syringaldehyde, cinnamic acid, 4-hydroxybenzoic acid, and p-coumaric acid. The hydrolysis rate of oat-spelt xylan by XynA was influenced by temperature, being unable to hydrolyze at 40 °C in the presence of tannic acid. On hydrolysis at 60 °C, the presence of gallic and tannic acid caused a major reduction in reducing sugar production, generating 3.74 and 2.15 g.L^-1 of reducing sugar, respectively, whereas the reaction in the absence of phenols generated 4.41 g.L^-1. When XynA was pre-deactivated by phenols it could recover most of its activity at 40 °C, however, at 60 °C activity could not be reestablished.     

Dehydroascorbate reduction

Dehydroascorbic acid is generated in plants and animal cells by oxidation of ascorbic acid. The reaction is believed to occur by the one-electron oxidation of ascorbic acid to semidehydroascorbate radical followed by disproportionation to dehydroascorbic acid and ascorbic acid. Semidehydroascorbic acid may recycle to ascorbic acid catalyzed by membrane-bound NADH-semidehydroscorbate reductase. However, disproportionation of the free radical occurs at a rapid rate, 10⁵ M^–1 s^–1, accounting for measurable cellular levels of dehydroascorbate. Dehydroascorbate reductase, studied earlier and more extensively in plants, is now recognized as the intrinsic activity of thioltransferases (glutaredoxins) and protein disulfide isomerase in animal cells. These enzymes catalyze the glutathione-dependent two-electron regeneration of ascorbic acid. The importance of the latter route of ascorbic acid renewal was seen in studies of GSH-deficient rodents (Meister, A. (1992)Biochem. Pharmacol. 44 1905–1915). GSH deficiency in newborn animals resulted in decreased tissue ascorbic acid and increased dehydroascorbate-to-ascorbate ratios. Administration of ascorbic acid daily to GSH-deficient animals decreased animal mortality and cell damage from oxygen stress. A cellular role is proposed for dehydroascorbate in the oxidation of nascent protein dithiols to disulfides catalyzed in the endoplasmic reticulum compartment by protein disulfide isomerase.