Showing papers on "Ascorbic acid published in 1981"
TL;DR: It is shown that, at physiological concentrations, urate reduces the oxo-heme oxidant formed by peroxide reaction with hemoglobin, protects erythrocyte ghosts against lipid peroxidation, and protects ERYthrocytes from peroxidative damage leading to lysis.
Abstract: During primate evolution, a major factor in lengthening life-span and decreasing age-specific cancer rates may have been improved protective mechanisms against oxygen radicals. We propose that one of these protective systems is plasma uric acid, the level of which increased markedly during primate evolution as a consequence of a series of mutations. Uric acid is a powerful antioxidant and is a scavenger of singlet oxygen and radicals. We show that, at physiological concentrations, urate reduces the oxo-heme oxidant formed by peroxide reaction with hemoglobin, protects erythrocyte ghosts against lipid peroxidation, and protects erythrocytes from peroxidative damage leading to lysis. Urate is about as effective an antioxidant as ascorbate in these experiments. Urate is much more easily oxidized than deoxynucleosides by singlet oxygen and is destroyed by hydroxyl radicals at a comparable rate. The plasma urate levels in humans (about 300 microM) is considerably higher than the ascorbate level, making it one of the major antioxidants in humans. Previous work on urate reported in the literature supports our experiments and interpretations, although the findings were not discussed in a physiological context.
2,597 citations
TL;DR: Relative availabilities determined for a series of meals containing ascorbic acid, eggs, orange juice, tea, coffee, cola, or whole wheat bread show that the method accurately reflects actual food iron availability.
685 citations
TL;DR: The results suggest that collage polypeptide synthesis, posttranslational hydroxylations, and activities of the twohydroxylases are independently regulated by ascorbate.
Abstract: After prolonged exposure to ascorbate, collagen synthesis in cultured human skin fibroblasts increased approximately 8-fold with no significant change in synthesis of noncollagen protein. This effect of ascorbate appears to be unrelated to its cofactor function in collagen hydroxylation. The collagenous protein secreted in the absence of added ascorbate was normal in hydroxylysine but was mildly deficient in hydroxyproline. In parallel experiments, lysine hydroxylase (peptidyllysine, 2-oxoglutarate:oxygen 5-oxidoreductase, EC 1.14.11.4) activity increased 3-fold in response to ascorbate administration whereas proline hydroxylase (prolyl-glycyl-peptide, 2-oxoglutarate:oxygen oxidoreductase, EC 1.14.11.2) activity decreased considerably. These results suggest that collage polypeptide synthesis, posttranslational hydroxylations, and activities of the two hydroxylases are independently regulated by ascorbate.
464 citations
Journal Article•
TL;DR: In this article, a male volunteer who had ingested vegetable juice, as a source of nitrate, and proline was found to have a detectable increase in NPRO in urine.
Abstract: Endogenous formation of N-nitrosoproline (NPRO) was demonstrated by monitoring its excretion in the urine of a male volunteer who had ingested vegetable juice, as a source of nitrate, and proline. The resulting NPRO was analyzed after derivatization by combined gas-liquid chromatography thermal energy analysis. The amount of total NPRO excreted in the urine was found to be proportional to the proline dose and increased exponentially with the nitrate dose ingested. Neither nitrate nor proline, when taken alone, led to a detectable increase in NPRO in urine. The amounts of NPRO formed (as estimated from the amounts excreted within 24 hr) after dosing 325 mg nitrate (NO3-) followed by 500 mg proline, ranged from 16.6 to 30.0 (mean, 23.3) micrograms per person. The simultaneous intake of ascorbic acid or alpha-tocopherol inhibited nitrosation of proline in vivo. Monitoring of NPRO or other N-nitroso compounds excreted in the urine thus appears to be a suitable procedure for estimating daily human exposure to endogenously formed N-nitroso compounds.
364 citations
TL;DR: The inactivation reaction is dependent on the state of adenylylation of the glutamine synthetase, suggesting that this a physiologically important reaction, and mixed-function oxidases are now implicated in the process of intracellular protein turnover.
Abstract: We partially purified a preparation from Escherichia coli that proteolytically degrades the enzyme glutamine synthetase [L-glutamate:ammonia ligase (ADP-forming), EC 6.3.1.2]. The degradation is at least a two-step process. First, the glutamine synthetase undergoes an oxidative modification. This modification leads to loss of catalytic activity and also renders the protein susceptible to proteolytic attack in the second step. The oxidative step displays characteristics of a mixed-function oxidation, requiring both molecular oxygen and a reduced nucleotide. This step can also be catalyzed by a purified, mammalian cytochrome P-450 system, as well as by a model system consisting of ascorbic acid and oxygen. Catalase blocks this oxidative modification step. Thus, the overall process of proteolytic degradation can be observed only if care is taken to remove catalase activity from the extracts. The inactivation reaction is dependent on the state of adenylylation of the glutamine synthetase, suggesting that this a physiologically important reaction. If so, then mixed-function oxidases are now implicated in the process of intracellular protein turnover.
343 citations
TL;DR: It is confirmed that the catechol compound electrochemically detected in the striatum is the direct metabolite of the DA, i.e. DOPAC, and support the thesis of a functional relationship between AA levels and dopaminergic neurotransmission.
285 citations
TL;DR: It was concluded that adaily intake of at least 140 mg is required for smokers to reach steady state concentrations and total body pools comparable to nonsmokers for whom a daily intake of about 100 mg was previously reported to be appropriate.
253 citations
TL;DR: Lactoferrin containing physiological amounts of iron is an inhibitor of lipid peroxidation induced by iron(III) salts and ascorbic acid and might therefore help to protect neutrophils, inflammatory foci and secretions from metal-ion-dependent oxidative damage.
Abstract: Lactoferrin containing physiological amounts of iron is an inhibitor of lipid peroxidation induced by iron(III) salts and ascorbic acid. It might therefore help to protect neutrophils, inflammatory foci and secretions from metal-ion-dependent oxidative damage.
248 citations
TL;DR: In order to further investigate the cooperation between ascorbate and vitamin E in suppressing lipid peroxidation, a liposomal system containing polyunsaturated phospholipids was used and the mixture of antioxidants was much more effective than the sum of both vitamins alone.
231 citations
TL;DR: Ascorbic acid supplementation at a dose of 500 mg per day for a brief period of 15 days resulted in an increase in the plasma ascorbate level temporarily, but it did not lower the blood glucose level of the diabetic patients.
Abstract: In contrast to normal subjects diabetic patients and very low plasma ascorbic acid and significantly high (p less than 0.001) dehydroascorbic acid irrespective of age, sex, duration of the disease, type of treatment, and glycemic control. However, there was no significant difference between the mean leukocyte ascorbate concentrations of the two populations. The in vitro rates of dehydroascorbate reduction in the hemolysate and the erythrocyte reduced glutathione levels and the glucose-6-phosphate dehydrogenase activities, which regulate the dehydroascorbate reduction, were similar in normal and diabetic subjects. The turnover of ascorbic acid was higher in the diabetics than that in the normal volunteers. Experiments with diabetic rats indicated that the increased turnover of ascorbic acid was probably due to increased oxidation of ascorbate to dehydroascorbate in tissue mitochondria. Ascorbic acid supplementation at a dose of 500 mg per day for a brief period of 15 days resulted in an increase in the plasma ascorbate level temporarily, but it did not lower the blood glucose level of the diabetic patients.
220 citations
TL;DR: This chapter discusses the differentiated state of normal and malignant cells, and the extent and the composition of the extracellular matrix is an important differentiated trait of tendon cells.
Abstract: Publisher Summary This chapter discusses the differentiated state of normal and malignant cells. The first step of cell separation (trypsinization and collagenase treatment), by removing membranous receptors and matrix elements and structures, produces a discontinuity between the cell and its environment. Thus, if the outside directs what (and how much) the cell should or should not produce, the flow of information may never be exactly the same. There are two exceptions to this. The extent and the composition of the extracellular matrix is an important differentiated trait of tendon cells. The tendon in vivo produces an extensive and organized matrix consisting primarily of collagen bundles. In the presence of ascorbic acid, these cells produce an extensive matrix also in culture. The organization of the matrix, however, is not analogous to the tendon in vivo. Both in scanning and transmission electron micrographs, the matrix appears as a mesh-like network where collagen bundles have a smaller diameter than the bundles observed in intact tendon. This may be because tendon cells in vivo are lined up in orderly arrays, while in culture they have little or no orientation especially at subconfluent stages. If cells in culture are made to line up by providing them with a preformed collagenous matrix, it may be possible to achieve an organized deposition of a de novo synthesized matrix.
TL;DR: Data is reported concerning the relative contribution of these two enzymes in maintaining the ascorbic acid system in the reduced state.
TL;DR: In this paper, the authors present a mechanism in which the ascorbate radical ion is in equilibrium with a dimer, which reacts with hydrogen ion, or with other proton donors present including water and buffers (at rates depending upon their acid strengths).
Abstract: Existing data on the kinetics of ascorbate radical decay, together with some new data on the effects of temperature, ionic strength, and presence of phosphate buffers, suggest a mechanism in which the ascorbate radical ion is in equilibrium with a dimer. This dimer reacts with hydrogen ion, or with other proton donors present including water and buffers (at rates depending upon their acid strengths), to form the disproportionation products ascorbate ion and dehydroascorbate acid.
TL;DR: In this article, a summary of information on the redox characteristics of the various species generated in the oxidation of ascorbate in water is presented, as well as studies on the kinetics and stochastic properties of the reaction.
Abstract: Ascorbic acid was utilized as a source of reducing equivalents in a multicomponent system that promotes the photoreduction of water. A summary of information on the redox characteristics of the various species generated in the oxidation of ascorbate in water is presented. Structures are given for ascorbic acid, ascorbate ion (HA/sup -/), dehydroascorbic acid, protonated ascorbate radical, and ascorbate radical. Data relevant to protonation equilibria, thermodynamic aspects, and reduction potentials are given as well as studies on the kinetics and stoichiometry of ascorbate oxidation reactions. The results of these studies illustrate some of the complexities of ascorbate as a reductant. Depending upon the pH and the propertes of the oxidant, H/sub 2/A, HA/sup -/, and/or A/sup 2 -/ may be the kinetically significant reducing agent(s). There is a discussion of the reactivities of the ascorbate radical/ascorbate couples toward outer-sphere redox reactions in terms of the driving force for the electron-transfer reaction and the intrinsic electron-transfer barrier associated with each of the reactants; and there is a brief discussion of the kinetics of the reduction of dehydroascorbic acid. (MWF)
TL;DR: A permeability increase was always observed after a certain lag, indicating that accumulation of peroxidized products in membranes may cause perturbation leading to loss of barrier function, since large molecules such as dextran could be released in the same way as glucose.
TL;DR: The relevance of these observations to rheumatoid arthritis and inflammatory joint diseases is discussed.
TL;DR: In this paper, a Rapid and Sensitive Method for the Determination of Ascorbic Acid using 4,7-Diphenyl-l,10-phenanthroline.
Abstract: (1981). A Rapid and Sensitive Method for the Determination of Ascorbic Acid using 4,7-Diphenyl-l,10-phenanthroline. Agricultural and Biological Chemistry: Vol. 45, No. 5, pp. 1289-1290.
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TL;DR: Some of the first clues that ascorbic acid might be involved in iron metabolism came from careful clinical observations of the Bantu in South Africa.
Abstract: Some of the first clues that ascorbic acid might be involved in iron metabolism came from careful clinical observations of the Bantu in South Africa.1 Habituated to the practice of drinking large q...
TL;DR: It is important to recognize and identify clinical illnesses in which immunologic dysfunctions are of nutritional origin, and Correction of malnutrition should lead to prompt reversal of acquired immune Dysfunctions.
Abstract: Immune system dysfunction can result from single-nutrient deficiencies or excesses, alone or in combination with generalized protein-energy malnutrition. Acquired immune dysfunctions in man occur with deficiencies of iron, zinc, vitamins A and B12, pyridoxine, and folic acid and with excesses of essential fatty acids and vitamin E. Additional micronutrients are important for maintaining immunologic competence in animals. Deficits or excesses of many trace elements and single nutrients thus have potential for causing immune dysfunctions in man. Since nutritionally induced immune dysfunction is generally reversible, it is important to recognize and identify clinical illnesses in which immunologic dysfunctions are of nutritional origin. Correction of malnutrition should lead to prompt reversal of acquired immune dysfunctions. (JAMA1981;245:53-58)
TL;DR: Ascorbic acid had a statistically significant effect on all parameters, including anthocyanin loss under both oxygen and nitrogen environments, catechin loss, increase in browning and polymeric color, decrease in Hunter “a” value and increase in Hunter L value as discussed by the authors.
Abstract: Interactions between ascorbic acid, pelargonidin-3-glucoside, and catechin were studied in pH 3.4 citrate-phosphate buffer at 20°C under anaerobic and oxygenated conditions. Changes in anthocyanin pigment, ascorbic acid, dehydroascorbic acid, and catechin were quantitatively measured during 130 days storage along with Hunter color parameters, browning, and polymeric color. Ascorbic acid had a statistically significant effect on all parameters, including anthocyanin loss under both oxygen and nitrogen environments, catechin loss, increase in browning and polymeric color, decrease in Hunter “a” value and increase in Hunter L value. Ascorbic acid bleached anthocyanin pigment and also induced browning. There is evidence that anthocyanin pigment and ascorbic acid degrade through a direct condensation mechanism.
TL;DR: The antioxidative effect of α-tocopherol incorporated into lecithin liposomes was studied in this paper, where the peroxidation reaction was catalyzed by ascorbic acid and Fe 2+ and did not involve singlet oxygen, superoxide, hydrogen peroxide, or a hydroxyl radical.
TL;DR: It is concluded that anomalous binding patterns are not necessarily an indication of binding to multiple sites or involvement of distinct receptors for high‐affinity agonist and antagonist binding.
Abstract:
I. Binding of [3H]apomorphine to dopaminergic receptors in rat striatum was most reproducible and clearly detectable when incubations were run at 25°C in Tris-HCl buffer, pH 7.5, containing 1 mM-EDTA and 0.01% ascorbic acid, using a washed total-membrane fraction. The receptor binding was stereospecifically inhibited by (+)-butaclamol, and dopamine agonists and antagonists showed high binding affinity for these sites. Unlabelled apomorphine inhibited an additional nonstereospecific binding site, which was unrelated to dopamine receptors. EDTA in the incubation mixture considerably lowered nonstereospecific [3H]apomorphine binding, apparently by preventing the complexation of the catechol moiety with metal ions which were demonstrated in membrane preparations. Stereospecific [3H]apomorphine binding was not detectable in the frontal cortex, whereas in the absence of EDTA much saturable nonstereospecific binding occurred. II. Kinetic patterns of stereospecific [3H]spiperone and [3H] apomorphine binding to rat striatal membranes and the inhibition patterns of a dopamine antagonist and an agonist were evaluated at different temperatures in high-ionic-strength Tris buffer with salts added and low-ionic-strength Tris buffer with EDTA. Apparent KD, values of spiperone decreased with decreasing tissue concentrations. KD, values of both spiperone and apomorphine were little influenced by temperature changes. Scatchard plots of the stereospecific binding changed from linear to curved; the amount of nonstereospecific binding of the 3H ligands varied considerably, but in opposite directions for spiperone and apomorphine in the different buffers. In various assay conditions, interactions between agonists, and between antagonists, appeared fully competitive, but agonist-antagonist interactions were of mixed type. The anomalous binding patterns are interpreted in terms of surface phenomena occurring upon reactions of a ligand with complex physicochemical properties and nonsolubilized sites on membranes suspended in a buffered aqueous solution. It is concluded that anomalous binding patterns are not necessarily an indication of binding to multiple sites or involvement of distinct receptors for high-affinity agonist and antagonist binding.
TL;DR: High-performance liquid chromatography on a Zorbax NH2 analytical column with acetonitrile used as eluant has allowed the separation of ascorbic acid, erythorbic acid; dithiothreitol is found to be effective in rapidly reducing dehydroascorbic Acid to asCorbic Acid, providing the basis for indirectly determining dehydroasiatic acid after its reduction.
TL;DR: Both adrenaline and EDTA block the manifestation of the lipoperoxidative capacity of brain subcellular fractions and simultaneously protect the Na,K-ATPase activity against inhibition.
TL;DR: The proposition that Delta-6-desaturase (D6D) loss is not only a marker of aging but a cause of some of its major manifestations is amenable to experimental test even in humans.
TL;DR: Multiple logistic analyses indicated that low vitamin C intake is an independent contributor to risk of severe cervical dysplasia when age and sexual activity variables are controlled.
Abstract: A case-control study of women with cervical abnormalities identified through Pap smears, was conducted in the Bronx, New York, to explore the relationship between nutritional intake and cervical dysplasia. Nutrient intake was estimated from computer analysis of three-day food records and 24-hour recall for 169 study participants (87 cases, 82 controls), including a subset of 49 pairs matched for age, race and parity. Mean vitamin C intake per day from three-day food record for controls was 107 mg, compared to 80 mg for cases (p less than 0.01). Analysis of matched pairs showed similar results; 29% of cases compared to 3% of controls in matched subset had vitamin C intake less than 50% of the recommended daily allowance, yielding a ten-fold increase in risk of cervical dysplasia as estimated by odds ratio (p less than 0.05). Younger age, greater frequency of sexual intercourse and younger age at first intercourse were associated with higher risk of cervical dysplasia. Multiple logistic analyses indicated that low vitamin C intake is an independent contributor to risk of severe cervical dysplasia when age and sexual activity variables are controlled. Approximately 35% of US women in their reproductive years have daily vitamin C intake below 30 mg, and 68% have vitamin C intake below 88 mg. If other studies confirm these findings, it may be important to explore a possible protective role of supplementary vitamin C for women at high risk of cervical cancer.
01 Jan 1981
TL;DR: Cell surface glycoproteins are regarded as exceedingly primitive features, probably first elaborated by wall-less Archaebacteria as cell surface protection (Lamport 1980).
Abstract: Morphogenetic machines perform according to preprogrammed design by assembling a vastly intricate pattern woven out of cell secretions. Thus eukaryotic cells, both plant and animal, embed themselves in a surprisingly similar extracellular matrix containing hydroxyproline-rich glycoproteins. Mention any other amino acid and the comparison would be trivial; but hydroxyproline occurs in few proteins, has no codon, and must be synthesized by post-translational modification of prolyl residues via prolyl hydroxylase, a remarkable enzyme catalyzing the direct fixation of molecular oxygen and a concomitant stoichiometric decarboxylation of α-ketoglutaric acid with ascorbic acid as a cofactor. Furthermore, hydroxyproline-rich glycoproteins have been with us virtually since the origin of the Chlamydomonas type where they comprise the major, if not the only component of a cellulose-free cell wall. Thus from an evolutionary point of view we can regard cell surface glycoproteins as exceedingly primitive features, probably first elaborated by wall-less Archaebacteria as cell surface protection (Lamport 1980). The role of plant cell wall proteins is less clear (Lamport 1965, 1970, 1977). This chapter will summarize recent results and major conclusions.
TL;DR: Amperometric glucose electrodes are constructed on the basis of glucose oxidase and peroxidase, and the electrodes possess a linear dependence of the stationary current on the glucose concentration in the range of 0.01-1 mM.