Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.6.5.4 (SOR)
720 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Ascorbic acid content and redox-enzymes activities of AA system are determined in four population of Dasypyrum villosum adapted to live in different environments. In D. villosum from the driest and warmest environment (Pachino), AFR reductase and AA peroxidase have activities lower than in the other populations. The results point out the role of AA peroxidase as the main "scavenger" of the H2O2 produced by cell metabolism.
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PMID:Ascorbate system in Dasypyrum villosum from different environments. 181 96

Ascorbate was maintained in the media during a long-term culture by HL-60 cells. The chemical oxidation of ascorbate was reversed in vitro by living HL-60 cells and was related to the amount of cells added. The increase of NADH concentration by lactate addition to cells was accompanied by an increase of both ascorbate regeneration and ferricyanide reduction. Further, plasma membrane enriched fractions from HL-60 cells revealed enhancement of both ascorbate regeneration and ferricyanide reduction in the presence of NADH when previously treated with detergent. The blockage of cell surface carbohydrates by wheat germ agglutinin (WGA) and Concanavalina ensiformis (Con A) lectins significantly inhibited the regeneration of ascorbate caused by the cells. These results support the idea that ascorbate is externally regenerated by the NADH-ascorbate free radical reductase as a part of the transplasma membrane redox system.
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PMID:Ascorbate is regenerated by HL-60 cells through the transplasmalemma redox system. 200 84

The role of ascorbic acid in scavenging free radicals was evaluated in a model of mammalian colonic epithelium homogenized in physiologic buffer and exposed to ionizing radiation. Ascorbic acid interacts with hydroxyl free radicals, resulting in production of the ascorbate free radical (AFR). Colonic mucosa contains a soluble factor that is heat sensitive, PCA precipitable and is contained within 1,000 MW dialysis tubing; it uses GSH and cysteine to reduce AFR. The factor from rat colon is fractionated between 55 and 70% saturation with solid (NH4)2SO4; a 3-4 fold increase in enzyme activity was achieved. We suggest that the factor is a cytosolic enzyme appropriately referred to as soluble AFR-reductase. This information provides insight into the mechanism by which ascorbic acid protects against damage by hydroxyl free radicals.
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PMID:Ascorbic acid metabolism in protection against free radicals: a radiation model. 216 65

The three steps in the synthesis of aldosterone (11 beta/18-hydroxylations and aldehyde synthetase) were examined in mitochondria from bovine glomerulosa and fasciculata to study the regulation of aldehyde synthetase. Ascorbate plus NADH shows synergism with malate in stimulating aldehyde synthetase without affecting 11 beta/-18-hydroxylations. The concentration of semidehydroascorbate reductase in mitochondria from glomerulosa is more than twice that from fasciculata. We propose that in glomerulosa, ascorbate provides a source of reducing equivalents that specifically support the last step in the synthesis of aldosterone.
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PMID:Ascorbate as a source of reducing equivalents for the synthesis of aldosterone. 239 91

We have demonstrated in rat adrenal (Natarajan, R.D. and Harding, B.W. (1985) J. Biol. Chem. 260, 3902-3905) that NADH-semidehydroascorbate reductase and ascorbate participate in an electron transport pathway (ETP) supplying reducing equivalents from NADH to cytochrome P-450scc. Here, we demonstrate that this ascorbate dependent ETP also supplies reducing equivalents to cytochrome P-450(11 beta/18) in both rat adrenal and bovine adrenal cortex. The activity is dependent upon addition of catalase or upon 'cold shock' treatment of isolated mitochondria. Comparison of the rates of 11 beta- and 18-hydroxylation supported by this ETP and by the classical pathway supported by various TCA cycle intermediates suggests that in vivo the ascorbate dependent pathway may be essential for maximal flow of reducing equivalents to the mitochondrial hydroxylases. Partial reconstitution of the ascorbate dependent 11 beta/18-hydroxylase activity was achieved with purified bovine outer mitochondrial and inner mitochondrial membranes fortified with supernatant from sonified mitochondria all preincubated with phosphatidyl choline. These preparations no longer require catalase or 'cold shock' treatment. Ascorbate and NADH-semidehydroascorbate reductase are unable to support 17 alpha- or 21-hydroxylase activity in isolated bovine adrenal cortical microsomes whether incubated with purified outer mitochondrial membranes or not.
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PMID:The function of NADH-semidehydroascorbate reductase and ascorbic acid in corticosteroid hydroxylation. 366 95

Rat adrenal mitochondria have an active rotenone-insensitive outer mitochondrial membrane NADH-semidehydroascorbate (NADH-SDA) reductase which supports cholesterol side chain cleavage at a rate equal to that supported by malate. Side chain cleavage activity supported by both of these electron donor systems is equally inhibited by cycloheximide. Catalase or butylated hydroxyanisole are required for the NADH-SDA reductase-supported cholesterol side chain cleavage. This requirement can be removed by briefly subjecting the mitochondrial preparations to -20 degrees C. Ascorbic acid alone or with malate is either inhibitory or has no effect on side chain cleavage activity. These observations demonstrate that outer mitochondrial membrane NADH-SDA reductase in rat adrenal functions to provide cytoplasmic reducing equivalents to intramitochondrial cytochrome P-450scc and provides a new explanation for the function of ascorbic acid in corticosteroidogenesis.
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PMID:Cholesterol side chain cleavage in rat adrenal supported by outer mitochondrial membrane NADH-semidehydroascorbate reductase. 398 Apr 58

The effects of ozone or sulfur dioxide on antioxidant enzymes were investigated in Arabidopsis thaliana. Plants were fumigated with 0.1-0.15 ppm ozone or sulfur dioxide up to about 1 week in an environment-controlled chamber. Both pollutants increased the activities of ascorbate peroxidase and guaiacol peroxidase in leaves, but had little effect on the activities of superoxide dismutase, catalase, monodehydroascorbate reductase, dehydroascorbate reductase or glutathione reductase. Ozone was more effective than sulfur dioxide in increasing the activities of the peroxidases. Ascorbate peroxidase activity increased 1.8-fold without a lag period during fumigation with 0.1 ppm ozone, while guaiacol peroxidase activity increased 4.4-fold with a 1-day lag. Expression of the APX1 gene encoding cytosolic ascorbate peroxidase was further investigated. Its protein levels in leaves exposed to 0.1 ppm ozone for 4 or 8 days were 1.5-fold higher than in controls. Both ozone and sulfur dioxide elevated APX1 mRNA levels in leaves at 4 and 7 days, whereas at 1 day only ozone was effective. The induction of APX1 mRNA levels by ozone (3.4- to 4.1-fold) was more prominent than that by sulfur dioxide (1.6- to 2.6-fold). The APX1 mRNA level increased by day and decreased by night. Exposure of plants to 0.1 ppm ozone enhanced the APX1 mRNA level within 3 h, which showed a diurnal rhythm similar to that of the control. These results demonstrate that near-ambient concentrations of ozone as well as similar concentrations of sulfur dioxide can induce APX1 gene expression in A. thaliana.
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PMID:Expression of Arabidopsis cytosolic ascorbate peroxidase gene in response to ozone or sulfur dioxide. 853 47

Chloroplast-targeted overexpression of an Fe superoxide dismutase (SOD) from Arabidopsis thaliana resulted in substantially increased foliar SOD activities. Ascorbate peroxidase, glutathione reductase, and monodehydroascorbate reductase activities were similar in the leaves from all of the lines, but dehydroascorbate reductase activity was increased in the leaves of the FeSOD transformants relative to untransformed controls. Foliar H2O2, ascorbate, and glutathione contents were comparable in all lines of plants. Irradiance-dependent changes in net CO2 assimilation and chlorophyll a fluorescence quenching parameters were similar in all lines both in air (21% O2) and at low (1%) O2. CO2-response curves for photosynthesis showed similar net CO2-exchange characteristics in all lines. In contrast, values of photochemical quenching declined in leaves from untransformed controls at intercellular CO2 (Ci) values below 200 microL L-1 but remained constant with decreasing Ci in leaves of FeSOD transformants. When the O2 concentration was decreased from 21 to 1%, the effect of FeSOD overexpression on photochemical quenching at limiting Ci was abolished. At high light (1000 micromol m-2 s-1) a progressive decrease in the ratio of variable (Fv) to maximal (Fm) fluorescence was observed with decreasing temperature. At 6(o)C the high-light-induced decrease in the Fv/Fm ratio was partially prevented by low O2 but values were comparable in all lines. Methyl viologen caused decreased Fv/Fm ratios, but this was less marked in the FeSOD transformants than in the untransformed controls. These observations suggest that the rate of superoxide dismutation limits flux through the Mehler-peroxidase cycle in certain conditions.
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PMID:Overexpression of iron superoxide dismutase in transformed poplar modifies the regulation of photosynthesis at low CO2 partial pressures or following exposure to the prooxidant herbicide methyl viologen. 962 9

Plasma membranes isolated from wild-type Saccharomyces cerevisiae crude membrane fractions catalyzed NADH oxidation using a variety of electron acceptors, such as ferricyanide, cytochrome c, and ascorbate free radical. Plasma membranes from the deletion mutant strain coq3delta, defective in coenzyme Q (ubiquinone) biosynthesis, were completely devoid of coenzyme Q6 and contained greatly diminished levels of NADH-ascorbate free radical reductase activity (about 10% of wild-type yeasts). In contrast, the lack of coenzyme Q6 in these membranes resulted in only a partial inhibition of either the ferricyanide or cytochrome-c reductase. Coenzyme Q dependence of ferricyanide and cytochrome-c reductases was based mainly on superoxide generation by one-electron reduction of quinones to semiquinones. Ascorbate free radical reductase was unique because it was highly dependent on coenzyme Q and did not involve superoxide since it was not affected by superoxide dismutase (SOD). Both coenzyme Q6 and NADH-ascorbate free radical reductase were rescued in plasma membranes derived from a strain obtained by transformation of the coq3delta strain with a single-copy plasmid bearing the wild type COQ3 gene and in plasma membranes isolated form the coq3delta strain grown in the presence of coenzyme Q6. The enzyme activity was inhibited by the quinone antagonists chloroquine and dicumarol, and after membrane solubilization with the nondenaturing detergent Zwittergent 3-14. The various inhibitors used did not affect residual ascorbate free radical reductase of the coq3delta strain. Ascorbate free radical reductase was not altered significantly in mutants atp2delta and cor1delta which are also respiration-deficient but not defective in ubiquinone biosynthesis, demonstrating that the lack of ascorbate free radical reductase in coq3delta mutants is related solely to the inability to synthesize ubiquinone and not to the respiratory-defective phenotype. For the first time, our results provide genetic evidence for the participation of ubiquinone in NADH-ascorbate free radical reductase, as a source of electrons for transmembrane ascorbate stabilization.
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PMID:Genetic evidence for coenzyme Q requirement in plasma membrane electron transport. 993 49

The distribution of antioxidants between bundle sheath and mesophyll cells of maize leaves was analysed in plants grown at 20 degrees C, 18 degrees C and 15 degrees C. The purity of the isolated bundle sheath and mesophyll fractions was determined using compartment-specific marker enzymes. In plants grown at 15 degrees C, ascorbate peroxidase, CuZn-superoxide dismutase (CuZn-SOD) and monodehydroascorbate reductase activities were increased in the bundle sheath cells, and glutathione reductase, dehydroascorbate reductase and monodehydroascorbate reductase activities were enhanced in the mesophyll cells. SOD was absent from the mesophyll of plants grown at 20 degrees C but an Fe-SOD activity was found in the mesophyll of plants grown at 15 degrees C. Foliar Mn-SOD activities were decreased at 15 degrees C compared to 20 degrees C. Catalase was undetectable in the mesophyll extracts of plants grown at 15 degrees C. Ascorbate and glutathione contents were considerably higher in the mesophyll than the bundle sheath fractions of plants grown at 20 degrees C. The ratios of reduced to oxidized forms of these antioxidants were significantly decreased in the bundle sheath, but increased in the mesophyll of leaves grown at 15 degrees C. Foliar H2O2 accumulated at 15 degrees C compared to 20 degrees C. Most of the foliar H2O2 was localized in the mesophyll tissues at all growth temperatures. The differential distribution of antioxidants between leaf bundle sheath and mesophyll tissues, observed at 20 degrees C, is even more pronounced when plants are grown at 15 degrees C and may contribute to the extreme sensitivity of maize to low temperatures.
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PMID:Low temperature-induced changes in the distribution of H2O2 and antioxidants between the bundle sheath and mesophyll cells of maize leaves. 1093 1


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