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)

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

Despite its fast autoxidation in vitro, ascorbate remains in its reduced form in vivo, indicating a special mechanism may be involved in its regeneration. The presence of an NADH-dependent reductase system, semidehydroascorbate reductase (SDR), for regeneration of ascorbate from its partially oxidized form, semidehydroascorbate (SDA), was demonstrated in bovine ocular tissues after extraction in Triton X-100. Highest SDR activity was detected in retinal extracts in the order of retina greater than pigment epithelium-choroid = ciliary body greater than iris. Minimal or no activity was observed in lens extracts or in aqueous fluid. Freezing and thawing, or boiling, destroyed the NADH-dependent SDR activity. NADH oxidation was significantly reduced (22% of total activity) when assays with retinal extracts were performed at 5 degrees C. Treatment with 4 mM, N-ethylmaleimide reduced the rate of NADH oxidation to 73 or 42% compared with control values with retinal or ciliary body extracts, respectively.
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PMID:Ascorbate regeneration in bovine ocular tissues by NADH-dependent semidehydroascorbate reductase. 375 16

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

Rat and feline brain and feline spinal cord were examined for the presence of semidehydroascorbate reductase (EC 1.6.5.4) and dehydroascorbate reductase (EC 1.8.5.1). Semidehydroascorbate reductase (SDAR), as monitored by both ascorbyl radical-dependent nicotinamide adenine dinucleotide (NADH) oxidase activity and NADH-dependent ascorbyl radical quenching, was present in all tissues studied. Rat cerebrum exhibited the highest levels and feline spinal cord the lowest. SDAR activity was about twice as high in feline cerebral cortex as in underlying white matter, and paralleled ascorbic acid levels. Subcellular fractionation of rat cerebrum localized most SDAR in a large granular fraction. In contrast, dehydroascorbate reductase was not detectable in any of the tissues examined. The results suggest that semidehydroascorbate reductase is the major enzyme catalyzing the regeneration of reduced ascorbic acid in the central nervous system.
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PMID:Reductive metabolism of ascorbic acid in the central nervous system. 399 84

Monodehydroascorbate reductase (EC 1.6.5.4) was purified from cucumber fruit to a homogeneous state as judged by polyacrylamide gel electrophoresis. The cucumber monodehydroascorbate reductase was a monomer with a molecular weight of 47,000. It contained 1 mol of FAD/mol of enzyme which was reduced by NAD(P)H and reoxidized by monodehydroascorbate. The enzyme had an exposed thiol group whose blockage with thiol reagents inhibited the electron transfer from NAD(P)H to the enzyme FAD. Both NADH and NADPH served as electron donors with Km values of 4.6 and 23 microM, respectively, and Vmax of 200 mol of NADH and 150 mol of NADPH oxidized mol of enzyme-1 s-1. The Km for monodehydroascorbate was 1.4 microM. The amino acid composition of the enzyme is presented. In addition to monodehydroascorbate, the enzyme catalyzed the reduction of ferricyanide and 2,6-dichloroindophenol but showed little reactivity with calf liver cytochrome b5 and horse heart cytochrome c. The kinetic data suggested a ping-pong mechanism for the monodehydroascorbate reductase-catalyzed reaction. Cucumber monodehydroascorbate reductase occurs in soluble form and can be distinguished from NADPH dehydrogenase, NADH dehydrogenase, DT diaphorase, microsome-bound NADH-cytochrome b5 reductase, and NADPH-cytochrome c reductase by its molecular weight, amino acid composition, and specificity of electron acceptors and donors.
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PMID:Monodehydroascorbate reductase from cucumber is a flavin adenine dinucleotide enzyme. 405 27

Coated vesicles were isolated from rat liver in about 80% fraction purity as determined from electron microscopy and analyses of marker enzymes and compared with Golgi apparatus and other membrane fractions isolated in parallel. The fractions were enriched in NADH-monodehydroascorbate reductase, ascorbate oxidase and ascorbic acid. The NADH-monodehydroascorbate reductase and ascorbate oxidase of the Golgi apparatus and coated vesicles differed from that of the endoplasmic reticulum in being inhibited by the sodium selective ionophore, monensin, at physiological concentrations while these activities were stimulated by ethylenediaminetetraacetic acid in coated vesicles but not in Golgi apparatus. Activities of both coated vesicles and Golgi apparatus fractions depleted in the coat protein, clathrin, were activated by the addition of clathrin-rich supernatant fractions. The results are discussed in the context of monodehydroascorbate as an acceptor for electron transport-mediated transfer of electrons from NADH by coated vesicles as part of a possible mechanism to drive membrane translocations or to acidify the interiors of vesicles.
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PMID:Monodehydroascorbate as an electron acceptor for NADH reduction by coated vesicle and Golgi apparatus fractions of rat liver. 614 8

NADH semidehydroascorbate oxidoreductase activity is present in clathrin coated vesicles isolated from rat liver. The activity of the enzyme on the coated vesicles and Golgi apparatus but not that of endoplasmic reticulum is stimulated by calmodulin and is inhibited by three different drugs which are known inhibitors of calmodulin function including trifluoperizine, pimozide and R24571. Extraction of clathrin from the vesicles causes a decrease in activity which can be partially restored when the extracted clathrin is added back. Added calmodulin also restores much of the activity which is lost when the clathrin is removed and the specific activity of added pure calmodulin is similar to that of the crude clathrin on a protein basis. There is a decrease in enzyme activity if coated vesicles or Golgi apparatus are treated with a calcium antagonist (8-[N,N-diethylamino]-octyl-3,4,5-trimethoxybenzoate) (TMB-8). However, the enzyme activity can be recovered to that of the untreated control if calcium (6.0 mM) is added. An additive stimulatory effect on enzyme activity is also observed when both calcium (1.0 mM) and calmodulin (40 micrograms/ml) are present in the vesicles simultaneously. The results show that the NADH-semidehydroascorbate oxidoreductase of coated vesicles and Golgi apparatus have regulatory properties different from those of the microsomal electron transport system. Calmodulin-calcium control mediated through the semidehydroascorbate reductase, may be among the components that regulate Golgi apparatus secretion.
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PMID:Calmodulin-NADH semidehydroascorbate oxidoreductase interactions of clathrin coated vesicles. 662 33

Enzymatic activity of NADH-monodehydroascorbate reductase could be observed in red blood cell membranes. This activity was latent in right side out as well as inside out vesicles. Apart from this latency addition of certain detergents led to activation of the enzyme also in open membrane preparations. The enzyme was inhibited by metal chelators, and displayed a very low apparent Michaelis constant. Monodehydroascorbate is a candidate for the natural electron acceptor of the transmembrane NADH-oxido-reductase. The activation by detergent may be due to enhancement of lipid fluidity or to exposure of a lipophilic substrate binding site.
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PMID:NADH-monodehydroascorbate reductase in human erythrocyte membranes. 667 13

To investigate the diabetogenic effect of pure dehydroascorbic acid, male Wister- and Sprague-Dawley rats received i.v. injections of the substance. No hyperglycemia and no decreased glucose tolerance were found. I.v. administration of the hydrolysis products of dehydroascorbic acid and of a solution containing monodehydroascorbate likewise did not increase blood glucose values. It is concluded that in previously performed experiments not dehydroascorbic acid itself but one or several impurities might have produced hyperglycemia in the rat. The electron transfer proteins tested (ascorbate:ferricytochrome b5 oxidoreductase, cytochrome b5, NADH:ferricytochrome b5 oxidoreductase, NADH:monodehydroascorbate oxidoreductase), which might participate in the reduction of dehydroascorbic acid, could not be induced in liver microsomes from Wistar rats by the injection of dehydroascorbic acid, its hydrolysis products, or monodehydroascorbate.
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PMID:Reinvestigation of the diabetogenic effect of dehydroascorbic acid. 685 59

In this paper, we show that human neuroectodermal cells exposed to 1-5 mM hydrogen peroxide or 10 nM-1 mM ascorbate die by programmed cell death induced by oxidative stress. The cell death by peroxide occurs within 4 h and involves approximately 80% of B-mel melanoma cells, while ascorbate causes cell death of approximately 86% of B-mel cells within 24 h. SK-N-BE(2) neuroblastoma cells are more resistant, 32% and 43% cell death for peroxide and ascorbate, respectively. In all cases, cell death causes hypodiploic DNA staining, evaluated by flow cytometry. Both cell lines can efficiently metabolise ascorbate due to significant levels of NADH-dependent semidehydroascorbate reductase and glutathione-dependent dehydroascorbate reductase. The cell death observed suggests a pro-oxidant, rather than anti-oxidant, role for ascorbic acid at physiological concentrations under these experimental conditions.
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PMID:Cell death by oxidative stress and ascorbic acid regeneration in human neuroectodermal cell lines. 757 46


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