Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.10.3.3 (ascorbate oxidase)
 778 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Enzymic memory is a kinetic phenomenon observable in double displacement mechanisms. The defining feature of enzymic memory is the occurrence of different rates of transfer for a common transferable group from the substituted enzymes obtained with different donor substrates. Memory behavior was previously demonstrated for both the bovine and human liver rhodaneses (EC 2.8.1.1). Steady state kinetic tests for enzymic memory have now been done with ascorbate oxidase (EC 1.10.3.3) and aspartate aminotransferase (EC 2.6.1.1). The results were positive with ascorbate oxidase, which showed an oxygen reactivity ratio of 1:20:300 for the reduced enzymes obtained with reductate, araboascorbate, and ascorbate, respectively. Results were negative for the aminotransferase tested with the alternate donors glutamate and cysteine sulfinate, with oxaloacetate as the common acceptor. The structural basis of the ascorbate oxidase results was probed by comparison of both the ultraviolet absorption and fluorescence spectra of the oxidized enzyme with those of the reduced forms obtained with ascorbate and reductate. The results are consistent with a conformational basis for the memory phenomenon.
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PMID:Enzymic memory. Steady state kinetic and physical studies with ascorbate oxidase and aspartate aminotransferase. 47 84

Voltammetric carbon fiber electrodes and a measuring protocol were designed to monitor extracellular changes in rat brain ascorbic acid (AA). Very fast variations of AA (less than 60 s in duration) as well as much slower changes can be followed. Basal and stimulated levels of AA, determined with the enzyme ascorbate oxidase (AAO), confirm the detection is selective for AA. Microinjections of glutamate (Glu) into various brain regions gave rise to rapid electrochemical signals ascribed to the efflux of AA into the extracellular fluid.
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PMID:Dynamic changes in extracellular fluid ascorbic acid monitored by in vivo electrochemistry. 167 9

Na(+)-dependent Ca2+ uptake in rat brain microsomal membrane vesicles was inhibited by preincubating the vesicles with ascorbic acid at 0.1-10 mM. The inhibitory effect of ascorbate was blocked by simultaneous addition of ascorbate oxidase. The decrease in activity was not reversed upon removing the ascorbate. The kinetic study showed that the treatment with ascorbate decreased Bmax without a change in Km for Ca2+. The inhibitory effect by ascorbate was also observed in membrane vesicles derived from osmotically shocked synaptosomes and in reconstituted membrane vesicles. The effect by ascorbate was specific: it did not affect either ATP-dependent Ca2+ uptake in the presence of o-phenanthroline, an inhibitor of lipid peroxidation, or Na(+)-dependent glutamate uptake in the membrane vesicles. The activity of Na(+)-Ca2+ exchange was also decreased by isoascorbic acid, but not by ascorbate 2-sulfate at 1 mM. The treatment with glutathione or 2-mercaptoethanol did not affect the Na(+)-Ca2+ exchange activity, while 1 mM dithiothreitol caused the inhibition which was completely blocked by o-phenanthroline. The effect of ascorbate on Na(+)-dependent Ca2+ uptake was observed even under the conditions which suppress peroxidation of membrane phospholipids.
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PMID:Decrease of Na(+)-Ca2+ exchange activity by ascorbate in rat brain membrane vesicles. 228 9

Extracellular brain ascorbate fluctuates with neuronal activity. There is previous evidence that the release of ascorbate is triggered by the re-uptake of neuronally released glutamate. This hypothesis predicts that drugs which block the release and re-uptake of glutamate will also block the release of ascorbate. In the present experiments we have used a novel dialysis electrode which allows continuous monitoring of physiologically induced ascorbate release from the striatum in freely moving rats. An infusion of the enzyme ascorbic acid oxidase abolished the increase in oxidation current in response to tail-pinch, which identified it as an ascorbate current. Perfusion with tetrodotoxin reduced the response to 25% and with CdCl2 to 4% of control. Perfusion with the uptake blocker L-trans-pyrrolidine-2,4-di-carboxylate reduced the response to 24% of control. A neuroprotective function for this coupling of ascorbate and glutamate release is discussed.
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PMID:The physiologically induced release of ascorbate in rat brain is dependent on impulse traffic, calcium influx and glutamate uptake. 781 14

The in vivo measurement of the rapid changes in the extracellular concentrations of L-glutamic acid in the mammalian brain during normal neuronal activity or following excessive release due to episodes of anoxia or ischemia has not been possible to this date. Current techniques for the measurement of the release of endogenous glutamate into the extracellular space of the central nervous system are relatively slow and do not measure the actual concentration of free glutamate in the extracellular space. An enzyme-based electrode with rapid response times (about 1 s) and high degree of sensitivity (less than 2 microM) and selectivity for L-glutamic acid is described in this paper. This electrode has both L-glutamate and ascorbate oxidase immobilized on its surface. The latter enzyme removes almost completely any interferences produced by the high levels of extracellular ascorbate present in brain tissue. The response of the electrode to glutamate and other potentially interfering substances was fully characterized in vitro and its selectivity, sensitivity and rapidity in responding to a rise in extracellular glutamate concentrations was also demonstrated in vivo. Placement of the electrode in the dentate gyrus of the hippocampus led to the detection of both KCl-induced release of L-glutamic acid and the release induced by stimulation of the axons in the perforant pathway. The development of this selective, sensitive and rapidly responding glutamate sensor should make it now possible to measure the dynamic events associated with glutamate neurotransmission in the central nervous system.
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PMID:Direct measurement of glutamate release in the brain using a dual enzyme-based electrochemical sensor. 782 Jun 52

The effect of ascorbic acid on Ca2+ uptake in cultured rat astrocytes was examined in the presence of ouabain and monensin, which are considered to drive the Na(+)-Ca2+ exchanger in the reverse mode. Ascorbic acid at 0.1-1 mM inhibited Na(+)-dependent Ca2+ uptake significantly but not Na(+)-dependent glutamate uptake in the cells, although the inhibition required pretreatment for more than 30 min. The effect of ascorbic acid on the Ca2+ uptake was blocked by simultaneous addition of ascorbate oxidase (10 U/ml). Na(+)-dependent Ca2+ uptake was also inhibited by isoascorbate at 1 mM but not by ascorbate 2-sulfate, dehydroascorbate, and sulfhydryl-reducing reagents such as glutathione and 2-mercaptoethanol. The inhibitory effect of ascorbic acid was observed even in the presence of an inhibitor of lipid peroxidation, o-phenanthroline, or a radical scavenger, mannitol, and the degrading enzymes such as catalase and superoxide dismutase. On the other hand, the inhibitory effect was not observed under the Na(+)-free conditions that inhibited the uptake of ascorbic acid in astrocytes. When astrocytes were cultured for 2 weeks in a medium containing ascorbic acid, the content of ascorbic acid in the cells was increased and conversely Na(+)-dependent Ca2+ uptake was decreased. These results suggest that an increase in intracellular ascorbic acid results in a decrease of Na(+)-Ca2+ exchange activity in cultured astrocytes and the mechanism is not related to lipid peroxidation.
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PMID:Intracellular ascorbic acid inhibits the Na(+)-Ca2+ exchanger in cultured rat astrocytes. 789 Oct 80

D-Serine normally contributes up to 3% to total plasma serine and up to 23% in chronic renal failure. D-Serine is metabolized by tubular D-amino acid oxidase (D-AAO), and high D-serine plasma levels are nephrotoxic; both events are localized in the straight part of the proximal tubule. We therefore investigated if and how D-serine is reabsorbed there. We microinfused 14C-labeled D- or -L-serine + [3H]inulin into early proximal (EP), late proximal (LP), or early distal (ED) tubule sections of superficial nephrons and into long loops of Henle (LLH) of rats in vivo and in situ. The fractional reabsorption (FR) of the 14C label was determined from the 14C:3H ratio in the final urine. At 0.36 mM, FR of D-[14C]serine was 86% (EP), 90% (LP), and approximately 0 (ED, LLH). FR of D-serine could be saturated and inhibited by L-serine (and vice versa). D-methionine, but not D-glutamate or D-arginine, blocked FR of D-serine (LP). We conlude that filtered D-serine is able to enter the pars recta cells, thereby getting access to D-AAO. The uptake carrier has a very low stereospecificity and is, therefore, different from that in the proximal convolution. The colocalization of exclusive reabsorption and metabolism makes the pars recta the tubule site for the recycling of the carbon structure of D-amino acids and, at the same time, the target of D-serine nephrotoxicity.
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PMID:D-Serine is reabsorbed in rat renal pars recta. 1036 74

The distributions of D-amino acid oxidase (D-AAO, EC 1.4.3.3) and D-aspartate oxidase (D-AspO, EC 1.4.3.1) activities were examined on several tissues of various fish species. Both enzyme activities were commonly high in kidney and liver and low in intestine with some exceptions. After oral administration of D-alanine at 5 micromol /g body weight(-1)day(-1) to carp for 30 days, D-AAO activity increased by about 8-, 3-, and 1.5-fold in intestine, hepatopancreas, and kidney, respectively, whereas no increase was found in brain. In contrast, oral administration of D-glutamate or D-aspartate did not show any increase of D-AspO activity in any tissues. D-AAO and D-AspO of common carp kidney and hepatopancreas were subcellularly localized in peroxisomes, as clarified in mammals. D-proline was the best substrate for D-AAO in rainbow trout kidney, common carp kidney, and hepatopancreas, followed by D-alanine and D-phenylalanine. N-methyl-D-aspartate was the best substrate for D-AspO in rainbow trout kidney and common carp hepatopancreas. The optimal pH for D-AAO in rainbow trout kidney was broad, from 7.4 to 8.2, and that for D-AspO was around 10. D-AAO was inhibited by benzoate known as D-AAO inhibitor and D-AspO was strongly inhibited by meso-tartarate as D-AspO inhibitor. From these results, at least D-AAO in fish is considered to work as a metabolizing agent of exogenous and endogenous free D-alanine that is abundant in aquatic invertebrates such as crustaceans and bivalve mollusks, which are potential food sources of these fishes.
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PMID:Distribution and characteristics of D-amino acid and D-aspartate oxidases in fish tissues. 1254 Dec 99

A new glass capillary microelectrode for L-glutamate is described using pulled glass capillaries (tip size, approximately 12.5 microm) with a very small volume (approximately 2 microl) of inner solution containing glutamate oxidase (GluOx) and ascorbate oxidase. The operation of the electrode is based on capillary action that samples L-glutamate into the inner solution. The enzyme reaction by GluOx generates hydrogen peroxide that is detected at an Os-gel-HRP polymer modified Pt electrode in a three-electrode configuration. The amperometric response behavior of the electrode was characterized in terms of the capillarity, response time, sensitivity and selectivity for measurements of L-glutamate. The currents at 0 V vs. Ag/AgCl increased linearly with the L-glutamate concentration from 10 to 150 microM for in vitro and in situ calibrations. The response was highly selective to L-glutamate over ascorbate, dopamine, serotonin and other amino acids. The detection of L-glutamate in the extracellular fluids of different regions of mouse hippocampal slices under stimulation of KCl was demonstrated.
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PMID:A glass capillary microelectrode based on capillarity and its application to the detection of L-glutamate release from mouse brain slices. 1255 24

A microfluidic device integrated with a nanoliter volume enzyme pre-reactor and an enzyme-modified electrode was developed for the highly selective continuous measurement of glutamate (Glu). The device consists mainly of two glass plates. One plate incorporates an electrochemical cell that consists of working electrode (WE), reference electrode (RE) and counter electrode (CE). The WE is modified with a bilayer film of Os-polyvinylpyrridine-based mediator containing horseradish peroxidase (Os-gel-HRP). The WE was operated at -50 mV versus Ag. The other plate has a thin layer flow channel integrated with a pre-reactor. The reactor has a number of micropillars (20 microm in diameter, 20 microm high and separated from each other by a 20 microm gap) modified with ascorbate oxidase (AAOx) to eliminate L-ascorbic acid (AA). The enzymatic oxidation of AA is superior to that obtained with our previously reported pre-electrolysis type micro-reactor since electrochemically reversible transmitters such as catecholamines do not provide a cathodic current at the WE. In addition, the high operation potential of the pre-reactor causes unknown electroactive species, which also cause interference at the detection electrode. As a result, we were able to detect 1 microM Glu continuously at a low flow rate even when AA concentration was 100 microM.
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PMID:Selective detection of L-glutamate using a microfluidic device integrated with an enzyme-modified pre-reactor and an electrochemical detector. 1283 43


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