Dehydroascorbic Acid Reduction in Several Tissues and Cultured Hepatocytes of the Chicken

Dehydroascorbic acid, the oxidized form of ascorbic acid, is rapidly reduced to ascorbate in living organs (ascorbate recycling). We examined the GSH-dependent dehydroascorbate reductase activity in several tissues of the chicken. The activity was highest in the liver, and second highest in the brain. The activity was localized in the cytosol fraction of the liver. We subsequently examined the dehydroascorbate reduction in separated chiken hepatocytes. The cellular ascorbate concentration was elevated in dehydroascorbate-treated cells. It is thought that hepatocytes incorporated external dehydroascorbate and converted it into ascorbate. These findings suggest that the liver plays an important role in ascorbate recycling by the chicken.     

Antioxidant Effect of the Reaction Mixture of Dehydroascorbic Acid with Tryptophan

Antioxidant activities as measured by the peroxide value, and the thiobarbituric acid or oxygen uptake methods were observed on a reaction mixture of dehydroascorbic acid with tryptophan. This was stronger than any of the activities of similar amino-carbonyl reaction mixtures tested and was comparable to BHA. The strongest activity was developed when an equimolar mixture of the reactants in 95% ethanol were heated for 30 min in a boiling water bath. In the antioxidant action, the presence of α-tocopherol acted synergistically. When the mixture was fractionated by TLC on a cellulose plate a brown colored fraction proved strongly effective by the POV method. Another fraction, effective in the oxygen uptake method but not in the POV method, was found mainly consisting of ascorbic acid. Other fractions which were identified before and related to the free radical formation were all inactive.     

Cerebral Astrocytes Transport Ascorbic Acid and Dehydroascorbic Acid Through Distinct Mechanisms Regulated by Cyclic AMP

Abstract: Cerebral ischemia and trauma lead to rapid increases in cerebral concentrations of cyclic AMP and dehydroascorbic acid (DHAA; oxidized vitamin C), depletion of intracellular ascorbic acid (AA; reduced vitamin C), and formation of reactive astrocytes. We investigated astrocytic transport of AA and DHAA and the effects of cyclic AMP on these transport systems. Primary cultures of astrocytes accumulated millimolar concentrations of intracellular AA when incubated in medium containing either AA or DHAA. AA uptake was Na⁺-dependent and inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), whereas DHAA uptake was Na⁺-independent and DIDS-insensitive. DHAA uptake was inhibited by cytochalasin B, d -glucose, and glucose analogues specific for facilitative hexose transporters. Once inside the cells, DHAA was reduced to AA. DHAA reduction greatly decreased astrocytic glutathione concentration. However, experiments with astrocytes that had been previously depleted of glutathione showed that DHAA reduction does not require physiological concentrations of glutathione. Astrocyte cultures were treated with a permeant analogue of cyclic AMP or forskolin, an activator of adenylyl cyclase, to induce cellular differentiation and thus provide in vitro models of reactive astrocytes. Cyclic AMP stimulated uptake of AA, DHAA, and 2-deoxyglucose. The effects of cyclic AMP required at least 12 h and were inhibited by cycloheximide, consistent with a requirement for de novo protein synthesis. Uptake and reduction of DHAA by astrocytes may be a recycling pathway that contributes to brain AA homeostasis. These results also indicate a role for cyclic AMP in accelerating the clearance and detoxification of DHAA in the brain.     

Effects of Sucrose and Citric Acid on the Viscometric Behavior of Aqueous Methylcellulose Solution

The flow of the mixture of methylcellulose (MC)—sucrose—citric acid—water was essentially thixotropic. The viscometric behaviors could be expressed by the power law, S = KDⁿ, where S was shearing stress and D rate of shear. The differential viscosity (ηd) of the mixture was strongly dropped by the addition of citric acid. Sucrose had the tendency to increase ηd of the mixtures except in the case of high sucrose concentration. From the results obtained, it has been concluded that citric acid tends to break the intermolecular hydrogen bonds of MC molecules, and that sucrose tends to keep the hydrogen bonds.     

Inhibition of Growth of Callus Cells by Degradation Products of Dehydroascorbic Acid

Candida pelliculosa var. acetaetherius was found to produce a β-glucosidase intracellularly. The enzyme was purified 200-fold by fractionation with ammonium sulfate and chromatography on Sephadex G-100 and DEAE Sepharose CL-6B. After polyacrylamide gel electrophoresis of the final fraction, one protein band corresponding to β-glucosidase was detected. The molecular weights determined by SDS-PAGE and by Sephacryl S-300 chromatography were 90,000 and 360,000, respectively, suggesting that the enzyme was a tetramer. The enzyme was a glycoprotein and its isoelectric point was at pH 4.9. It’s optimum pH and temperature were 6.5 and 50°C, respectively. The enzyme activity was inhibited by Zn^{2 +}, Hg^{2 +}, Cu^{2 +}, Co^{2 +}, p-chloromercuribenzoate, and glucose. Inhibition by glucose was competitive with a Ki value of 6.5 mm. Specificity studies for substrates indicated that the enzyme was specific for the p-configuration of sugars. Km values measured at 50°C were 0.5 mm for p-nitrophenyl-β-glucoside and 37 mm for cellobiose.     

Hydrolysis of Chitosan in Lactic Acid

The effects of molecular weight and the degree of acetylation on the hydrolysis of chitosan in dilute lactic acid were studied. It was demonstrated that the higher the values of both parameters, the more rapid the decreases in viscosity and the viscosity-average molecular weight of chitosan.     

Colorimetric Sensor of Cobalt Ions in Aqueous Solution Using Gold Nanoparticles Modified with Glycyrrhizic Acid

Plasmonics - The present work describes simple and green method for the preparation of gold nanoparticles (AuNPs) in aqueous medium under ambient condition and their use in colorimetric detection...     

ESR Spectral Studies on the Free Radical Formed by the Reaction of Dehydroascorbic Acid with Amino Acid

Acrylonitrile-hydrating activity was found in various bacteria belonging to the genera Arthrobacter, Corynebacterium, Microbacterium, Nocardia, Pseudomonas and Rhodococcus. A strain, N-774, isolated by acetonitrile enrichment culture from soil showed the highest activity. Taxonomic studies indicated that strain N-774 belonged to the genus Rhodococcus. The acrylonitrile-hydrating enzyme of strain N-774 was constitutively formed in the cells. Besides acrylonitrile, many nitriles were hydrated to the corresponding amides. «-Butyronitrile, suc- cinonitrile and chloroacetonitrille served as suitable substrates. This bacterium could utilize many aliphatic nitriles and amides as a sole source of nitrogen but hardly utilized malononitrile, acrylonitrile or acrylamide. Cells having high nitrile hydratase activity (about 50units/mg of dry cells) could be easily prepared by cultivation at 30°C for 40 hr in a malt extract and yeast extract medium.     

Spontaneous Oligomerization of Nucleotide Alternatives in Aqueous Solutions

On early Earth, a primitive polymer that could spontaneously form from likely available precursors may have preceded both RNA and DNA as the first genetic material. Here, we report that heated aqueous solutions containing 5-hydroxymethyluracil (HMU) result in oligomers of uracil, heated solutions containing 5-hydroxymethylcytosine (HMC) result in oligomers of cytosine, and heated solutions containing both HMU and HMC result in mixed oligomers of uracil and cytosine. Oligomerization of hydroxymethylated pyrimidines, which may have been abundant on the primitive Earth, might have been important in the development of simple informational polymers.     

Antioxidant and Prooxidant Effects of Ascorbic Acid, Dehydroascorbic Acid and Flavonoids on LDL Submitted to Different Degrees of Oxidation

Although a high intake of antioxidants may decrease the risk of developing cardiovascular diseases, under certain circunstances they may promote free radical generation and lipid peroxidation. The objectives of the present study were to determine the antioxidant effects of ascorbic acid (AA), dehydroascorbic acid (DHA) and flavonoids on LDL submitted to different degrees of oxidation. LDL was submitted to oxidation with CuCl₂ (2.4 μM). Before or at different times after the propagation of the oxidation process, 28 μM (5 μg/ml) of either AA or DHA or 5 μg/mL flavonoids extract were added. Alpha-tocopherol, conjugated dienes, thiobarbituric acid reacting substances (TBARS) and LDL electrophoretic mobility were determined as indices of LDL oxidation. The presence of any of the three antioxidants from the onset of the incubation delayed the oxidation process. However, the addition of both DHA and flavonoids to the oxidation process when it was already initiated and alpha-tocopherol consumed, accelerated the oxidation. In contrast, AA delayed the oxidation process even when added after alpha-tocopherol was consumed. Nevertheless, it also accelerated LDL oxidation when added during the propagation phase of the oxidation process. In conclusion: although AA, DHA and flavonoids delay LDL oxidation when added before the initiation of the process, they accelerate the process if added to minimally oxidized LDL.     

Effect of Ascorbic Acid on the Degradation of Cyanocobalamin and Hydroxocobalamin in Aqueous Solution: A Kinetic Study

The degradation kinetics of 5 × 10⁻⁵ M cyanocobalamin (B₁₂) and hydroxocobalamin (B_12b) in the presence of ascorbic acid (AH₂) was studied in the pH range of 1.0–8.0. B₁₂ is degraded to B_12b which undergoes oxidation to corrin ring cleavage products. B_12b alone is directly oxidized to the ring cleavage products. B₁₂ and B_12b in degraded solutions were simultaneously assayed by a two-component spectrometric method at 525 and 550 nm without interference from AH₂. Both degrade by first-order kinetics and the values of the rate constants at pH 1.0–8.0 range from 0.08 to 1.05 × 10⁻⁵ s⁻¹ and 0.22–7.62 × 10⁻⁵ s⁻¹, respectively, in the presence of 0.25 × 10⁻³ M AH₂. The t_1/2 values of B₁₂ and B_12b range from 13.7 to 137.5 h and 2.5–87.5 h, respectively. The second-order rate constants for the interaction of AH₂ with B₁₂ and B_12b are 0.05–0.28 × 10⁻² and 1.10–30.08 × 10⁻² M⁻¹ s⁻¹, respectively, indicating a greater effect of AH₂ on B_12b compared to that of B₁₂. The k_obs–pH profiles for both B₁₂ and B_12b show the highest rates of degradation around pH 5. The degradation of B₁₂ and B_12b by AH₂ is affected by the catalytic effect of phosphate ions on the oxidation of AH₂ in the pH range 6.0–8.0.KEY WORDS: ascorbic acid, cyanocobalamin, degradation, hydroxocobalamin, kinetics, two-component spectrometry     

Complexes of Tungsten(VI) with Mucic Acid: a Spectrophotometric and Polarimetric Study in Aqueous Solution

Spectrophotometric work on mucic acid-W(VI) system shows the formation of three different oxoanion complexes in aqueous solution; their stability is dependent upon pH. One of the complexes is monomeric tungstodimucate and the other two are 2/2 species. An anomalous cryoscopic behaviour, similar to that of W(VI) tartaric system, has been observed for the dimeric complex formed at higher pH. The stoichiometries and conditional dissociation constants have been polarimetrically determined by means of competitive reactions between the mucic and tartaric ligands. ¹H and ¹³C NMR spectra have been interpreted for the similar complex species of both mucic and tartaric acids.     

Optical Properties of DNA in Aqueous Solution

In the study of DNA electric birefringence, it is usual to use theories that consider that molecules in solution are small in relation to the light wavelength. In this work, we study the DNA electric birefringence using a broken-rod macroion (BRM) model composed of two cylindrical arms which does not restrict the size of the molecules. To achieve this, we include the inhomogeneity effect of the light electric field through the molecule and the interaction between its different parts. To analyze the interaction between a molecule and the incident beam of light, we apply the discrete dipole approximation (DDA), according to which each molecule is described as a finite array of electronic coupled oscillators. The electric birefringence is calculated from the oscillator polarizability. This is obtained from experimental data of electric birefringence saturation and from the increment of the solution refraction index in relation to that of the solvent. Furthermore, the oscillator polarizability is also estimated from DNA absorption spectrum using the Kronig–Kramers relations. This allows us to analyze the contributions of the different absorption bands of DNA to the electric birefringence. We analyze the influence of the inhomogeneity of the light electric field and of the intramolecular interactions in the characterization of DNA optical properties using electric birefringence measurements.     

Decomposition of Allyl Isothiocyanate in Aqueous Solution

Allyl isothiocyanate was gradually decomposed in aqueous solution to produce a garlic like odor. The decomposition of this isothiocyanate was not based on hydrolysis of R-NCS as in the case of p-hydroxybenzyl isothiocyanate, but the addition reaction on –N=C=S. Four substances formed with the decomposition of the isothiocyanate were isolated, and their chemical constitutions were clarified. Allyl isothiocyanate was decomposed to allyl allyldithiocarbamate (III), which was degradated to diallyl tetra- and penta-sulfide (II), and this poly-sulfide was further degradated to paraffin like hydrocarbon (I) and sulfur. Moreover, N,N′-diallylthiourea (IV) was produced by the addition reaction of allylamine, formed from the isothiocyanate by action of water, to residual isothiocyanate.