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At least 811 records · Page 45Linked to original sources
PubMed1998

Thioltransferase from Arabidopsis thaliana seed: purification to homogeneity and characterization.

Thioltransferase is a general GSH-disulfide reductase of importance for redox regulation. The protein thioltransferase has been purified to apparent homogeneity on SDS-PAGE from the Arabidopsis thaliana seed. The purification procedures included DEAE-cellulose ion exchange chromatography, Sephadex G-75 gel filtration, Q-Sepharose ion exchange chromatography, and DEAE-Sephadex A-25 ion exchange chromatography. The enzyme has a molecular mass of 22 kDa and a pI of 4.8, and it is heatstable. The protein had broad specificities for substrates ranging from low-molecular disulfides (S-sulfocysteine and cystine) to protein disulfides (trypsin and insulin). However, it could not reduce the disulfide linkages of ribonuclease A and bovine serum albumin. It could utilize non-disulfide substrates such as dehydroascorbic acid and alloxan. The protein can reduce the disulfide bond in 2-hydroxyethyl disulfide with an optimum pH of 8.5. Its activity was greatly activated by monothiol compounds such as reduced glutathione and L-cysteine.

Arabidopsis↗
PubMed1993

Ascorbate and dehydroascorbate measurements in aqueous solutions and plasma determined by gas chromatography-mass spectrometry.

The tert-butyldlmethylsllyl derivatives of ascorbic acid and dehydroascorbic acid were characterized by gas chromatography-mass spectrometry, and an isotope dilution assay for ascorbate and dehydroascorbate was developed using [13C6]ascorbic acid and [13C6]- and [6,6-2H2]dehydroascorbate. This assay was used to monitor ascorbic acid loss and the resulting rise of dehydroascorbic acid in aqueous solutions and plasma. Ascorbic acid was shown to rapidly decompose in aqueous solutions containing transition metal ions or when exposed to oxygen. Ethylenedlaminetetraacetic acid chelation did not prevent ascorbic acid degradation in aqueous solution, and ascorbate in ethylenedlaminetetraacetic acid chelated plasma was converted to dehydroascorbate on freezing. Gas chromatography-mass spectrometry appears to be a satisfactory method for determining the ascorbate and dehydroascorbate content of solutions including human blood plasma, whether or not there is ongoing oxidation of ascorbate in those solutions.

Ascorbic Acid↗
PubMed1991

Analysis of the mechanism of d-amphetamine-and apomorphine-induced changes of ascorbic acid catabolism in discrete brain areas of the rat.

Ascorbic acid (AA) levels and dehydroascorbic acid/ascorbic acid (DHAA/AA) ratios were determined in hypothalamus, striatum, and remaining brain of male Wistar rats, after single or repeated injections of d-amphetamine (1.8 mg/kg/day s.c.), apomorphine (1.0 mg/kg/day s.c.), and/or haloperidol (0.1 mg/kg/day i.p.). Major changes were observed in hypothalamus, in which all drugs significantly increased DHAA/AA ratio. Apomorphine and haloperidol consistently decreased AA level as well. The DHAA/AA ratio increase was observed also when apomorphine and d-amphetamine were associated with haloperidol. In striatum, apomorphine (single) and d-amphetamine (repeated) injections increased DHAA/AA ratios; such AA oxidation increase was inhibited by haloperidol; the increases (d-amphetamine) or decrease (apomorphine) of AA levels were also inhibited by haloperidol; haloperidol alone did not modify DHAA/AA ratio and induced minor changes of striatal AA level. In remaining brain, apomorphine (single) and d-amphetamine (repeated) treatment increased DHAA/AA ratio; such increase was observed also when haloperidol was associated with apomorphine or d-amphetamine; moreover, haloperidol by itself increased AA oxidation, although to a lesser extent than it did in hypothalamus. It is concluded that AA catabolism can be activated in the rat striatum by a dopaminergic mechanism; in hypothalamus and in remaining brain, the AA catabolism activation appears rather to be a non-specific effect of the pharmacological manipulation.

Animals↗
PubMed2004

Ascorbic acid in blood serum of patients with pulmonary tuberculosis and pneumonia.

Ascorbic acid plays a major role in pulmonary antioxidant defense. Sufficient amounts of ascorbic acid are necessary to maintain normal metabolic processes in the lung. We measured the levels of ascorbic, dehydroascorbic and diketogulonic acids in blood serum of patients with pulmonary tuberculosis (PTB) and pneumonia. The serum levels of ascorbic acid were decreased in PTB and pneumonia, and those of dehydroascorbic acid were decreased in PTB, but not in pneumonia. The serum diketogulonic acid levels were not significantly changed in either PTB or pneumonia. The ratio of ascorbic to dehydroascorbic acid levels in serum were increased in PTB, but in pneumonia we observed a significant decrease in this index. The ratio of dehydroascorbic to diketogulonic acid in PTB was decreased, but in pneumonia this index did not significantly differ from the control value. Thus, in PTB the rate of ascorbic acid oxidation is decreased and the rate of dehydroascorbic acid oxidation is increased. By contrast, in pneumonia the rate of ascorbic acid oxidation is increased, but the rate of dehydroascorbic acid oxidation did not differ from control values.

2,3-Diketogulonic Acid↗
PubMedDate not supplied

[The excretion of ascorbic acid and its metabolites in uremia and hemodialysis].

Renal excretion of ascorbic, dehydroascorbic and diketogulonic acids in uremia and relevant loss in hemodialysis are measured in comparison with those in patients with uremic syndrome (prior to hemodialysis) and in healthy subjects (control). Renal elimination of ascorbic acid was higher while of dehydroascorbic acid lower vs control. Elimination of diketogulonic acid was similar to control. In a session of hemodialysis, the organism loses 132.0 +/- 13.6 mg of ascorbic, 132.0 +/- 10.0 mg of dehydroascorbic and 204.0 +/- 9.0 mg of diketogulonic acid. 48-hour urinary losses of the patients reached 8.4 +/- 1.4, 19.6 +/- 1.1, 75.6 +/- 1.5 mg, respectively. Compared to control, hemodialysis patients lose the above acids 24.3, 2.7 and 4.6 times more.

2,3-Diketogulonic Acid↗
PubMedDate not supplied

Simultaneous determination of ascorbic, dehydroascorbic, isoascorbic, and dehydroisoascorbic acids in meat-based food products by liquid chromatography with postcolumn fluorescence detection: a method extension.

A simple and rapid liquid chromatographic (LC) method for determining ascorbic, dehydroascorbic, isoascorbic, and dehydroisoascorbic acids in mostly single-component food products was evaluated for use in analysis of multicomponent meat-based food products such as TV dinners. Ground-beef samples were used as blanks for repeatability studies. Samples were fortified with 5, 10, 20, and 40 ppm of mixed standards of ascorbic acid and isoascorbic acid. Means of 12 recoveries at 4 levels of fortification were 102.5 and 83.5%, respectively, for ascorbic acid and isoascorbic acid, with coefficients of variation of 6.7 and 15.2%, respectively. TV dinner products (21 samples) from a local grocery store were analyzed for vitamin C content. Samples prepared with a commercial food processor and a food grinder were compared. The commercial food processor was more capable than the food grinder in producing a homogeneous sample, which is critical to the method.

Ascorbic Acid↗
PubMed1984

Ascorbic acid content and accumulation by alveolar macrophages from cigarette smokers and nonsmokers.

The lung is at risk for injury from inhaled oxidants, including components of cigarette smoke; therefore, maintaining a chemical antioxidant defense would be advantageous. The potential for ascorbic acid to assume this protective role was investigated by comparing the total ascorbate content of alveolar macrophages obtained from human smokers and nonsmokers, from hamsters that were exposed to cigarette smoke for 4 to 6 weeks, and from a control group of unexposed hamsters. The abilities of alveolar macrophages from these four sources to accumulate 14C-labeled ascorbic acid and dehydroascorbate were also compared. The total ascorbate content in hamster macrophages was 19.5 +/- 1.7 and 44.3 +/- 2.8 nmol/10(7) cells for nonsmokers and smokers, (n = 5) and 73.8 +/- 13.1 nmol/10(7) cells (n = 13, p less than 0.1) for nonsmokers and smokers, respectively. In both humans and hamsters, the rates of accumulation of ascorbic acid and dehydroascorbate were significantly greater (p less than 0.05) for alveolar macrophages from smokers compared with nonsmokers of the same species. After internalization, greater than or equal to 70% of the dehydroascorbate was reduced to ascorbic acid by alveolar macrophages from nonsmokers and smokers of both species. An aqueous extract of cigarette smoke oxidized significantly more ascorbic acid to dehydroascorbate in vitro than a comparable volume of phosphate-buffered saline solution without smoke. The increased content of total ascorbate in alveolar macrophages from smokers and their enhanced ability to accumulate ascorbic acid and dehydroascorbate in vitro may reflect protective utilization of ascorbic acid under conditions of increased oxidant stress, compared with nonsmokers. In addition, alveolar macrophages may internalize dehydroascorbate that has been generated by oxidants in the alveolar space and reduce it to ascorbic acid so it can be reused as an antioxidant.

Adult↗
PubMed2004

Light-induced byproducts of vitamin C in multivitamin solutions.

BACKGROUND: When solutions of multivitamin preparations (MVPs) are exposed to light, H(2)O(2) as well as organic peroxides are generated and the concentration of vitamin C decreases. The aim of this study was to determine, using mass spectrometry, whether the generation of oxidative byproducts of vitamin C, such as dehydroascorbate (DHA) and 2,3-diketogulonic acid (DKG), accounted for the reported decrease in ascorbic acid in MVPs exposed to light. METHODS: Mass spectrometry was used to document the formation of byproducts of ascorbic acid in solutions containing a MVP, vitamin C + riboflavin, and vitamin C + H(2)O(2) + Fe(2+). The involvement of ascorbic acid and H(2)O(2) in the formation of organic peroxides was tested by measuring peroxide concentrations in solutions containing H(2)O(2) with or without ascorbic acid and with or without Fe(2+) before and after addition of catalase. RESULTS: The loss of ascorbic acid in photo-exposed MVPs was associated with the concomitant generation of byproducts different from DHA and DKG. Among them, one mass fingerprint was particularly observed with solutions of vitamin C + riboflavin exposed to ambient light as well as with the solution of vitamin C + H(2)O(2) + Fe(2+), suggesting a Fenton-like reaction. This fingerprint was associated with the formation of catalase-resistant peroxides. CONCLUSION: Exposure of MVPs to light leads to the rapid loss of ascorbic acid and generation of specific byproducts that differ from DHA and DKG. The conversion of vitamin C into byproducts could be of biological importance in accounting for the decrease in ascorbic acid concentrations and the generation of organic peroxides in light-exposed MVPs.

2,3-Diketogulonic Acid↗