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Showing papers on "Ascorbic acid published in 1986"


Journal ArticleDOI
TL;DR: The results indicated that enzymatically released calvaria cells can form mineralized bone nodules in vitro in the presence of ascorbic acid and organic phosphate.
Abstract: Single-cell suspensions obtained from sequential enzymatic digestions of fetal rat calvaria were grown in long-term culture in the presence of ascorbic acid, Na β-glycerophosphate, and dexamethasone to determine the capacity of these populations to form mineralized bone. In cultures of osteoblastlike cells grown in the presence of ascorbic acid and β-glycerophosphate or ascorbic acid alone, three-dimensional nodules (∼75 μm thick) covered by polygonal cells resembling osteoblasts could be detected 3 days after confluency. The nodules became macroscopic (up to 3 mm in diameter) after a further 3–4 days. Only in the presence of organic phosphate did they mineralize. Nodules did not develop without ascorbic acid in the medium. Dexamethasone caused a significant increase in the number of nodules. Histologically, nodules resembled woven bone and the cells covering the nodules stained strongly for alkaline phosphatase. Immunolabeling with specific antibodies demonstrated intense staining for type I collagen that was mineral-associated, a weaker staining for type III collagen and osteonectin, and undetectable staining for type II collagen. Nodules did not develop from population I and the number of nodules formed by populations II–V bore a linear relationship to the number of cells plated (r=.99). The results indicated that enzymatically released calvaria cells can form mineralized bone nodulesin vitro in the presence of ascorbic acid and organic phosphate.

859 citations


Journal ArticleDOI
TL;DR: Evidence is presented which supports the importance of vitamin C as a component of the overall antioxidant protective mechanisms found in cells and tissues and the protection by vitamin C of phagocytic cells involved in the defense against pathogen invasion.

639 citations


Journal ArticleDOI
TL;DR: It was not until 1753 that a Scottish physician, James Lind, systematically described scurvy and its prevention by dietary means, and for four decades the British navy refused to accept Lind's findings, and countless sailors continued to die unnecessarily from scurvard until lemon juice was finally included in sailors' rations.
Abstract: ASCORBIC acid, originally called vitamin C, is required for human health.1 In human beings deprived of ascorbic acid, the deficiency disease scurvy develops and can be life threatening. Although a disease remarkably similar to scurvy was described by the ancient Egyptians,2 , 3 it was not until 1753 that a Scottish physician, James Lind, systematically described scurvy and its prevention by dietary means.4 Even then, the dietary requirements were controversial. For four decades the British navy refused to accept Lind's findings, and countless sailors continued to die unnecessarily from scurvy until lemon juice was finally included in sailors' rations. Research since Lind's . . .

599 citations


Journal ArticleDOI
TL;DR: The present results provide a mechanistic explanation for the previous report that urate protects ascorbate from oxidation in human blood and demonstrate that another important 'antioxidant' property of uric acid is the ability to form stable co-ordination complexes with iron ions.
Abstract: In order to survive in an oxygen environment, aerobic organisms have developed numerous mechanisms to protect against oxygen radicals and singlet oxygen. One such mechanism, which appears to have attained particular significance during primate evolution, is the direct scavenging of oxygen radicals, singlet oxygen, oxo-haem oxidants and hydroperoxyl radicals by uric acid. In the present paper we demonstrate that another important 'antioxidant' property of uric acid is the ability to form stable co-ordination complexes with iron ions. Formation of urate-Fe3+ complexes dramatically inhibits Fe3+-catalysed ascorbate oxidation, as well as lipid peroxidation in liposomes and rat liver microsomal fraction. In contrast with antioxidant scavenger reactions, the inhibition of ascorbate oxidation and lipid peroxidation provided by urate's ability to bind iron ions does not involve urate oxidation. Association constants (Ka) for urate-iron ion complexes were determined by fluorescence-quenching techniques. The Ka for a 1:1 urate-Fe3+ complex was found to be 2.4 X 10(5), whereas the Ka for a 1:1 urate-Fe2+ complex was determined to be 1.9 X 10(4). Our experiments also revealed that urate can form a 2:1 complex with Fe3+ with an association constant for the second urate molecule (K'a) of approx. 4.5 X 10(5). From these data we estimate an overall stability constant (Ks approximately equal to Ka X K'a) for urate-Fe3+ complexes of approx. 1.1 X 10(11). Polarographic measurements revealed that (upon binding) urate decreases the reduction potential for the Fe2+/Fe3+ half-reaction from -0.77 V to -0.67 V. Thus urate slightly diminishes the oxidizing potential of Fe3+. The present results provide a mechanistic explanation for our previous report that urate protects ascorbate from oxidation in human blood. The almost saturating concentration of urate normally found in human plasma (up to 0.6 mM) represents 5-10 times the plasma ascorbate concentration, and is orders of magnitude higher than the 'free' iron ion concentration. These considerations point to the physiological significance of our findings.

527 citations


Journal ArticleDOI
TL;DR: A review of the history and present situation of drug abuse in the United States, as well as some of the aspects of drug rehabilitation that have changed over the years, is provided.
Abstract: SCOPE OF THIS REVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365 BIOSYNTHESIS AND REQUIREMENTS OF ASCORBIC ACID . . . . . . . . . . . . . . . . . . . . . . . . . 366 METABOLISM OF ASCORBATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367 ACTIONS AND FUNCTIONS OF ASCORBATE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368 DOPAMINE !3-HYDROXYLASE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . 372 PEPTIDYL GLYCINE a-AMIDATING MONOOXYGENASE... . . . . . . . . . . . . . . . . . . . . . . . . . . . 373 4-HYDROXYPHENYLPYRUV ATE DIOXYGENASE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374 PROL YL AND L YSYL HYDROXYLASES FOR COLLAGENS . . . . . . . . . . . . . . . . . . . . . . . . . . . 376 HYDROXYLATION OF OTHER PROTEINS . . . .. . . ...... . . . . 383 Elastin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383 C1q o/ Complement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384 DIOXYGENASE REACTIONS OF PYRIMIDINES AND NUCLEOSIDES . . . . . . . . . . . . . . 385 CARNITINE PATHWAY HYDROXYLASES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386 OTHER POSSIBLE FUNCTIONS OF ASCORBATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391 CONCLUDING REMARKS ... . . ........ . . . . . .. . .. . .. . . ...... .... . . ........ .... ..... . . . . 391

516 citations


Journal ArticleDOI
TL;DR: The results indicate that enhanced responding for CR following administration of psychomotor stimulant drugs is critically dependent on dopaminergic activation of the nucleus accumbens, rather than the caudate nucleus.
Abstract: Intra-accumbens d-amphetamine enhances responding for reward-related stimuli (conditioned reinforcers, CRs), whereas intra-caudate d-amphetamine has only weak and variable effects (Taylor and Robbins 1984). The present experiment further examined the involvement of the nucleus accumbens and the role of dopamine (DA) in this effect. Thirsty rats were trained to associate a flash of a light and movement of a dipper (CR) with water. After implantation of permanent guide cannulae aimed at the nucleus accumbens, they were assigned to one of four groups, receiving either bilateral 6-OHDA (4 mg/ml free base in 2 μ1 0.1% ascorbic acid/0.9% saline) or sham (vehicle) infusions into the nucleus accumbens or the caudate nucleus. In the test phase, two novel levers were available. Responding on one lever (CR lever) produced the light and dipper stimuli without water presentation, whereas responding on the other (NCR lever) had no effect. All four groups received four counterbalanced intra-accumbens infusions of d-amphetamine (3, 10, 20 μg/2 μl) or vehicle. On the 5th test day, subjects were pretreated subcutaneously with apomorphine (0.1 mg/kg). Intra-accumbens d-amphetamine in both sham-lesioned groups produced a dose-dependent increase in responding on the CR lever, but no significant change on the NCR lever. No selective increases in responding on either lever were found in animals with 6-OHDA-induced depletion of DA (>80%) in the nucleus accumbens following intra-accumbens d-amphetamine; however, in subjects with DA depletion of the posterior caudate nucleus (>80%), increases in responding on the CR lever were observed to be similar in magnitude to those of both the sham-lesioned groups. Following systemic administration of apomorphine, only rats in the nucleus-accumbens-lesioned group continued to respond, preferring the CR lever, thus suggesting the involvement of DA receptors in these effects. These results indicate that enhanced responding for CR following administration of psychomotor stimulant drugs is critically dependent on dopaminergic activation of the nucleus accumbens, rather than the caudate nucleus.

314 citations


Journal ArticleDOI
TL;DR: Ternary complexes of Cu(II) with acetylacetone and various salicylic acids were synthesized in pure state and these complexes were characterised by elemental analysis, conductivity, IR data and optical absorption as discussed by the authors.
Abstract: Ternary complexes of Cu(II) with acetylacetone and various salicylic acids (viz., salicylic, 5-chloro-, 3,5-dibromo-, 3,5-dinitro-, thio-, and acetyl-salicylic acids) were synthesised in pure state and these complexes were characterised by elemental analysis, conductivity, IR data and optical absorption. The antibacterial and antifungal activity studies on these complexes revealed that the ternary complexes are better toxic agents than the binary complexes against certain bacteria and fungi studied. The lipo-philic tendency of these complexes was also studied. Ascorbic acid markedly decreases the antimicrobial activity of the ternary complexes while traces of cobalt completely suppresses their toxic action in many cases. Based on these results probable mechanisms for the antimicrobial activity of these complexes are discussed.

278 citations


01 Jan 1986
TL;DR: In this paper, the effect of Ca infiltration on ascorbic acid content and on ethylene and carbon dioxide evolution in apples is presented, and a conceptual model on how Ca deficiency may lead to physiological disorders in fruits and vegetables is illustrated.
Abstract: It is known that calcium (Ca) plays an important role in maintaining quality and reducing physiological disorders that cause wastage in fruits and vegetables during storage. Recent studies indicate that the effect of Ca in retarding senescence is partly due to reductions in microviscosity of membranes associated with senescence. Data on the effect of Ca infiltration on ascorbic acid content and on ethylene and carbon dioxide evolution in apples are presented, and a conceptual model on how Ca deficiency may lead to physiological disorders in fruits and vegetables is illustrated. The value of Ca response manipulation in postharvest treatments is discussed. Ca-regulated cellular protein phosphorylation also is described.(wz)

274 citations


Journal ArticleDOI
TL;DR: Results show that, unlike other collagens, type VI collagen is assembled into tetramers before it is secreted from the cells, and they suggest an extracellular aggregation mechanism that appears to be unique to this collagen.
Abstract: Monoclonal antibodies reactive with the tissue form of type VI collagen were used to isolate the type VI collagen polypeptides from cultured fibroblasts and muscle cells. Two [35S]methionine-labeled polypeptides of 260 and 140 kD were found intracellularly, in the medium, and in the extracellular matrix of metabolically labeled cells. These polypeptides were disulfide cross-linked into very large complexes. The 260- and 140-kD polypeptides were intimately associated and could not be separated from each other by reduction without denaturation. In the absence of ascorbic acid, both polypeptides accumulated inside the cell, and their amounts in the medium and in the matrix were decreased. These results suggest that both the 260- and the 140-kD polypeptides are integral parts of the type VI collagen molecule. Examination of type VI collagen isolated from the intracellular pool by electron microscopy after rotary shadowing revealed structures corresponding to different stages of assembly of type VI collagen. Based on these images, a sequence for the intracellular assembly of type VI collagen could be discerned. Type VI collagen monomers are approximately 125 nm long and are composed of two globules separated by a thin strand. The monomers assemble into dimers and tetramers by lateral association. Only tetramers were present in culture media, whereas both tetramers and multimers were found in extracellular matrix extracts. The multimers appeared to have assembled from tetramers by end-to-end association into filaments that had prominent knobs and a periodicity of approximately 110 nm. These results show that, unlike other collagens, type VI collagen is assembled into tetramers before it is secreted from the cells, and they also suggest an extracellular aggregation mechanism that appears to be unique to this collagen.

254 citations


Journal ArticleDOI
TL;DR: Observations indicate that membrane alpha-tocopherol status can control the balance between pro- and antioxidant effects of ascorbic acid, and provide the most direct evidence to date that ascorBic acid interacts directly with components of the phospholipid bilayer.

225 citations


Journal ArticleDOI
TL;DR: It appears that Cu(II) bound to the tightest albumin-binding site is less available to the ascorbate than the more loosely bound cation, which generates OH radicals, which rapidly inter-react with the protein and modify it in a 'site-specific' manner.
Abstract: Exposure of albumin to Cu(II) (10-100 microM) and ascorbate (0.1-2 mM) results in extensive molecular modifications, indicated by decreased fluorescence and chain breaks. The rate of utilization of molecular oxygen and ascorbate as a function of Cu(II) concentration is non-linear at copper/albumin ratios of greater than 1. It appears that Cu(II) bound to the tightest albumin-binding site is less available to the ascorbate than the more loosely bound cation. SDS/polyacrylamide-gel electrophoresis reveals new protein bands corresponding to 50, 47, 22, 18 and 3 kDa. For such a cleavage pattern, relatively few (approximately 3) and rather specific chain breaks occurred. Repeated addition of portions of ascorbate to the albumin/Cu(II) mixture results in increased intensity of the new bands. The absence of Cu(II) or the presence of metal chelating agents is inhibitory. There was no evidence of intermolecular cross-linking or of the formation of insoluble, albumin-derived, material. A mechanism is proposed wherein the loosely bound Cu(II) participates in a Fenton-type reaction. This generates OH. radicals, which rapidly inter-react with the protein and modify it in a 'site-specific' manner.

Journal Article
TL;DR: The results indicate that ascorbic acid has a key physiologic role in facilitating the absorption of non-heme iron from the diet and that about 50 mg of the vitamin in each main meal is desirable for optimum effect.
Abstract: The effect of ascorbic acid on the absorption of non-heme iron was studied in 299 subjects. Different meals in which the non-heme iron was labelled with two different radio-iron isotopes were served with and without ascorbic acid to the same subject. Other meals containing foods with a known high content of ascorbic acid were also studied. Studies were also made giving different amounts of ascorbic acid with different meals. Marked differences in the enhancement of iron absorption were seen when ascorbic acid was given in different meals. It is suggested that ascorbic acid promotes iron absorption from the diet by reducing the negative effect on iron absorption of certain ligands such as phytates and tannins present in the diet. This interpretation is supported by observations that the most pronounced effects of ascorbic acid were found in meals with a high content of ligands known to inhibit iron absorption. Crystalline ascorbic acid and native ascorbic acid in foods appeared to have the same effect in promoting absorption of iron. The results indicate that ascorbic acid has a key physiologic role in facilitating the absorption of non-heme iron from the diet and that about 50 mg of the vitamin in each main meal is desirable for optimum effect.

Journal ArticleDOI
TL;DR: Resultats d'etudes par voltammetrie cyclique de l'oxydation du methyl-4 pyrocatechol, del'acide ascorbique, de l’acide (dihydroxy-3,4)-benzeneacetique, etc.
Abstract: Resultats d'etudes par voltammetrie cyclique de l'oxydation du methyl-4 pyrocatechol, de l'acide ascorbique, de l'acide (dihydroxy-3,4)-benzeneacetique, etc


BookDOI
01 Jan 1986
TL;DR: Hiskia et al. as mentioned in this paper studied the role of catalysts in photoelectrochemical phenomena, focusing on the performance of colloidal and heterogeneous redox catalysts.
Abstract: Photoinduced charge separation: Requirements needed for ideal relays and photosensitizers- Photoinduced charge separation: Towards the design of supermolecular systems based on transition metal complexes- Fundamental studies into primary events in photocatalysis employing CdS and TiO semiconductors: Photoluminescence, laser flash photolysis and pulse radiolysis- Dynamics of interfacial electron transfer reactions in colloidal semiconductor systems and water cleavage by visible light- Electronic Spectroscopy of semiconductor clusters- Catalysed decay of oxidising radicals in water- Photocatalysis and light-induced electron transfer reactions of tertiary amines- Photocatalytic production of ascorbic acid A secondary photosynthesis in plants- Spectroscopic and electrochemical studies of photochemical electron transfer in linked donor-acceptor molecules- Bifunctional porphyrins: Redox photochemistry of: meso(tritolyl(pyridyl Ru(III) (NH 3) 4 L')) porphyrin: (L'=NH 3, pyridine, 5-Cl-pyridine)- Linear chain platinum complexes as photocatalysts- Electron transfer reactions on extremely small semiconductor colloids studied by pulse radiolysis- Nafion stabilized aqueous solutions of colloidal semiconductors- In situ generated catalyst-coated colloidal semiconductor CdS particles in surfactant vesicles and polymerized surfactant vesicles- Development of catalysts for water photoreduction: Improvement, poisoning and catalytic mechanism- Radiolytic methods of preparation of colloidal and heterogeneous redox catalysts and their application in light-induced H2 generation from water- The effect of promoters on the photochemical water cleavage in suspensions of Pt-loaded TiO2 with increased light to chemical conversion efficiency- Metallic catalysts on semiconductors: Transparency and electrical contact properties- On the nature of the inhibition of electron transfer at illuminated p-type semiconductor electrodes- The importance of solution kinetics in photoelectrochemical phenomena- Mechanistic aspects of semiconductor photoelectrochemistry: The behavior of Si and GAAs in nonaqueous solvents- Charge injection into semiconductor particles - Importance in photocatalysis- Hydrogen evolution and selective organic photosynthesis catalyzed by zinc sulfide- Photocatalytic organic synthesis by use of semiconductors or dyes- A Hiskia and A Ioannidis Photocatalytic oxidation of organic compounds with heteropoly electrolytes Aspects on photochemical utilization of solar energy- Photoformation of hydrogen in liquid water in the presence of Pt/TiO2 catalyst and organic impurities- Surface properties of catalysts Iron and its oxides: Surface chemistry, photochemistry and catalysis- Photocatalysis over clay supports- Photoreduction and-oxidation of molecular nitrogen on titanium dioxide and titanium containing minerals- Photoassisted reduction of carbon and nitrogen compounds: with semiconductors- Adsorption and desorption processes in photocatalysis- Photo-induced processes at titanium dioxide surfaces- Photolysis of adsorbed phases: Ethanoic acid-insulators and semiconductors systems Influence of acid-base properties- Cadmium sulfide photocatalyzed hydrogen production from aqueous solutions of sulfite- Environmental photochemistry of chlorinated aromatics in aqueous media A review of data- Photodegradation of wastes and pollutants in aquatic environment- Heterogeneous photocatalysis for water purification: Prospects and problems- A Gas Research Institute perspective on inorganic synthesis of gaseous fuels- Putting photocatalysis to work- Panel discussion on the Selective activation and conversion of molecules- Panel discussion on Sensitization and immobilization of catalysts on various supports- Panel discussion on Electrocatalysis and photocatalysis- Final Remarks- Author Index

Journal ArticleDOI
TL;DR: All species of poultry are capable of AA synthesis and dietary supplementation with AA is not necessary when the animal is managed properly, however, when the birds are subjected to stressful condi...
Abstract: All species of poultry are capable of AA synthesis and dietary supplementation with AA is not necessary when the animal is managed properly. However, when the birds are subjected to stressful condi...

Journal ArticleDOI
TL;DR: The inhibition of autoxidation of plasma lipids by vitamin C (ascorbic acid) has been studied and it is suggested that this autoxidative destruction of ascorbate may play a role regulating its concentration in blood plasma.

Journal ArticleDOI
TL;DR: In this paper, the effects of four widely employed "antioxidants" on iron-mediated hydroxyl radical formation and lipid peroxidation were studied in aqueous model systems.
Abstract: The effects of four widely employed “antioxidants” on iron-mediated hydroxyl radical formation and lipid peroxidation were studied in aqueous model systems. Iron and copper served as catalysts for the reactions which oxidized ascorbic acid and alpha-tocopherol and reduced oxygen. Ferrous ion spontaneously reduced oxygen to O−2 (su-peroxide anion radical) which led to OH (hydroxyl radical) and H2O2 generation and lipid peroxidation. Precipitation or sequestration of iron greatly depressed these oxidative events. Complexation by EDTA and citric acid, however, formed catalytically active iron chelates. The concomitant increase in iron solubility explained the substantial enhancement of iron-driven redox reactions by EDTA and citric acid.

Journal ArticleDOI
TL;DR: In this article, the effect of different initial dissolved oxygen concentrations (0.41, 1.44, and 3.74 mg/L) on rate of deteriorative quality changes [ascorbic acid degradation, browning, hydroxymethylfurfural (HMF) and furfural production] in lemon juice stored at 36°C was investigated.
Abstract: The effect of different initial dissolved oxygen concentrations (0.41, 1.44, and 3.74 mg/L) on rate of deteriorative quality changes [ascorbic acid degradation, browning, hydroxymethylfurfural (HMF) and furfural production) in lemon juice stored at 36°C was investigated. No significant effects on rate of ascorbic acid degradation and furfural formation could be attributed to the different oxygen levels. Degradation of ascorbic acid appeared to be predominantly anaerobic. Lag period before browning increased depended on oxygen level. Zero-, first- and second-order kinetic models were fitted to various degradative reactions occurring in lemon juice during storage. Highly significant correlations were obtained between browning index, HMF, and furfural formation, suggesting that all three would be suitable as chemical indices of storage temperature abuse in lemon juices.

Journal ArticleDOI
TL;DR: The preparation of hydroxylated analogues of the decapeptide, in particular, may contribute to a better understanding of adhesion in the dopa-containing mussel glue protein.

Journal ArticleDOI
TL;DR: The main blood constituents which could interfere in clinical glucose measurements using a hydrogen peroxide based glucose electrode have been investigated using several different membranes and constant and sweeping potentials.

Journal Article
TL;DR: Ascorbic acid appears to be effective in lowering the body burden of these carcinogenic compounds, thus offering a rational basis for long-term intervention studies in this area of northern China.
Abstract: A total of 238 samples of 24-h urine were collected from inhabitants of high-risk (Lin-xian) and low-risk (Fan-xian) areas for esophageal cancer in northern China, according to three protocols: ( a ) from undosed subjects; ( b ) from subjects who had ingested 100 mg l-proline three times a day 1 h after each meal; and ( c ) from subjects in Lin-xian who had ingested 100 mg ascorbic acid together with 100 mg l-proline three times a day 1 h after each meal. As an index of individual exposure to N -nitroso compounds or their precursors, ingested in food and/or formed endogenously, the levels of four urinary N -nitrosamino acids and nitrate were determined. The amounts of N -nitrosoproline, N -nitrosothiazolidine 4-carboxylic acid, N -nitrososarcosine, and nitrate excreted in the 24-h urine of undosed subjects in Lin-xian were significantly higher than those in Fan-xian, indicating a higher exposure of the inhabitants in the high-risk area to N -nitroso compounds and their precursors. Ingestion of l-proline resulted in a marked increase in urinary N -nitrosoproline levels in inhabitants from both areas, suggesting that endogenous nitrosation may occur to a larger extent when appropriate amine precursors are ingested in foods. Intake of moderate doses of ascorbic acid by high-risk subjects effectively reduced the urinary levels of N -nitrosamino acids to those found in undosed subjects in the low-risk area. If N -nitroso compounds formed in vivo are among the causative factors for esophageal cancer in this area of northern China, ascorbic acid appears to be effective in lowering the body burden of these carcinogenic compounds, thus offering a rational basis for long-term intervention studies in this area.

Journal ArticleDOI
TL;DR: It is proposed that conversion of ferritin into haemosiderin in iron overload is biologically advantageous in that it decreases the ability of iron to promote oxygen-radical reactions.
Abstract: Horse spleen and human spleen ferritins increase the formation of hydroxyl radicals (OH) at both pH 4.5 and pH 7.4 in reaction mixtures containing ascorbic acid and H2O2. The generation of OH is inhibited by the chelator desferrioxamine. Human spleen haemosiderin also accelerates OH generation in identical reaction mixtures, but is far less effective (on a unit iron basis) than ferritin under all reaction conditions. It is proposed that conversion of ferritin into haemosiderin in iron overload is biologically advantageous in that it decreases the ability of iron to promote oxygen-radical reactions.

Journal ArticleDOI
TL;DR: A wide range of ascorbic acid levels in the aqueous humor was found, and most of the animals considered to be diurnal had higher ascor bicarbonate levels than the nocturnal animals, suggesting that ascorBic acid may play a protective role in those animals who are most exposed to light.
Abstract: • Ascorbic acid concentration is known to be very high in the aqueous humor of humans and most animals. The role it might play in ocular function is a subject of conjecture. Some have proposed that it might protect the eye against light-induced damage. We examined the aqueous humor from 22 species of mammals to determine the range of levels and to see if there was a correlation with behavior. A wide range of ascorbic acid levels in the aqueous humor was found. Most of the animals considered to be diurnal had higher ascorbic acid levels than the nocturnal animals. This would suggest that ascorbic acid in the aqueous humor may play a protective role in those animals who are most exposed to light. Regardless, any theory proposing a role for ascorbic acid in the eye in mammals must take the wide range of ascorbic acid levels into account.

Journal ArticleDOI
TL;DR: The bioavailability of iron added to different types of cows' milk formulas was studied using mono- isotopic and double-isotopic methods and the addition of ascorbic acid at concentrations of 100 mg/l or higher demonstrated its enhancing effect on iron absorption in fortified milks.

Journal ArticleDOI
TL;DR: In this paper, a water-soluble azo compound, 2,2'-azobis(2-amidinopropane) dihydrochloride, was administered intraperitoneally to mice to study the toxicological effects on biological tissues in vivo and their inhibition by chain-breaking antioxidants.

Journal ArticleDOI
TL;DR: The ascorbate binding site appears to consist of two cis-positioned coordination sites of the enzyme-bound iron and is thus partially identical to the binding site of 2-oxoglutarate, which suggests that asCorbate reduces the enzyme -bound iron through an "inner-sphere" mechanism.

Journal ArticleDOI
TL;DR: In this paper, ascorbic acid, dihydroxyphenylacetic acid, and dopamine were compared at polypyrrole-coated glassy carbon and naked glassy polynodes, and it was shown that the electrochemical reversibility differences for these substances are to some degree result of electrostatic interactions between the anionic solutes, or anionic reaction intermediates, and anionic functional groups on carbon or cationic fixed sites in oxidized poly pyrrole.

Journal ArticleDOI
TL;DR: It is concluded from the high activity of ascorbate peroxidase activity and the levels of antioxidants found that this enzyme can effectively remove low concentrations of peroxides.

Journal ArticleDOI
TL;DR: The partially purified enzyme requires only the addition of certain sulfhydryl compounds for catalytic activity, dithiothreitol being the most effective and suggesting a catalytic mechanism of this enzyme unlike that of the prolyl and lysyl hydroxylases.