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:1.10.3.3 (ascorbate oxidase)
778 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Endogenous material present in heat-denatured extracts of rat brain that inhibited the binding of [3H]-isopropyl-4-(2,1,3-benzoxadiazol-4-yl)-1,4-dihydro-5-metho xyca rbonyl-2,6-dimethyl-3-pyridinecarboxylate ([3H]-PN200-110) to calcium channels in brain membranes was purified. Spectrophotometric analysis of material purified by strong anion-exchange and reverse-phase chromatography showed an absorption maximum at 266 nm at pH 7.0 that shifted to 245 nm at pH 2.0. This pH-dependent spectral shift was indistinguishable from that of ascorbic acid. Samples of the purified extract contained ascorbic acid; however, the inhibition of binding by purified material was always greater than the inhibition seen with equivalent concentrations of ascorbate, implying the presence of additional inhibitory factors. Attempts to detect and identify such inhibitory substances by chromatography showed that inhibition activity was coincident with the presence of ascorbate, and the inhibitory activity of purified material was abolished after treatment with ascorbic acid oxidase. Iron enhanced the inhibition produced by ascorbate, and chemical analysis of purified preparations revealed the presence of iron. Studies comparing the potency of the purified material with that of a mixture of ascorbate plus iron showed that the content of ascorbate and iron in the purified brain extract is sufficient to explain the observed inhibition of binding of [3H]PN200-110.
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PMID:Identification of ascorbate as an endogenous substance that irreversibly inhibits binding of dihydropyridine calcium channel blockers. 153 95

The structural comparison of copper-containing proteins has provided a new dimension to the relationships suggested by sequence similarities. Ryden (1988) summarized the putative relationships, suggesting that a primordial single-domain cupredoxin evolved into the multidomain copper oxidases. The structures have revealed the fact that the differences reside primarily in insertions and deletions at junctions between secondary-structure elements. The mechanism of evolution (e.g., integration of new sequences into regions not essential to the Greek key fold) remains unknown. Which of the properties of a cupredoxin fold are necessary for function is the subject of site-directed mutagenesis studies. Can two of the ligands be interchanged (e.g., the upstream histidine and partially answered by the multidomain copper oxidase structure. The Tyr-Cys-Thr sequence in plastocyanin (in which threonine is a member of the hydrogen-bonding pair) is homologous with the His-Cys-His sequence in ascorbate oxidase. In the latter electron transfer is believed to flow from the type I copper (bound by the cysteine) to the trinuclear cluster, probably via these histidine residues. Hence, one might infer that the tyrosine and threonine have some role in electron transfer. Tyr-83 has been previously implicated in NMR studies as a primary site of electron transfer. The multi-copper protein structures have revealed interesting new features. The extra coppers are bound at domain interfaces, and can be single metals or the novel trinuclear cluster, depending on the availability of liganding histidines. A structural model of ceruloplasmin suggests that it will have at least two type I sites and, possibly, a third type I site such as stellacyanin (no methionine ligand), as well as a binding site for a trinuclear cluster. The similarity of the sequences of N2O reductases and a domain of cytochrome oxidase to the sequences of proteins with known structures suggests that these, too, will have Greek key domains. Galactose oxidase and hemocyanin do not have Greek key folds in their functional domains, although each does have a Greek key domain. The need for a Greek key fold remains obscure. The apoproteins are clearly stable without metals; there are examples other than immunoglobulins of Greek key folds. So far copper seems to be found in a very limited subset of structures; other chapters in this volume show that zinc, for example, has a much wider variety of environments in proteins, as does iron. It may be that the copper-containing Greek key proteins represent a very small evolutionary niche.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Copper protein structures. 179 5

It has been indicated recently that ascorbic acid is responsible for the hemoglobin-mediated oxidative damage to the central nervous system (Sadrzadeh & Eaton, J. Clin. Invest. 82:1510-1515, 1988). In this paper we describe the changes in chemiluminescence accompanying hemoglobin- and ascorbate-dependent oxidative injury to brain tissue. Addition of either hemoglobin (15 microM) or ascorbate (1 or 2 mM) to rat brain homogenates stimulated spontaneous chemiluminescence in a synergistic manner. This increase in chemiluminescence was inhibited by desferrioxamine indicating that free iron was involved in the reactions leading to lipid peroxidation. Preincubation with ascorbate oxidase inhibited both spontaneous and hemoglobin-dependent chemiluminescence, suggesting that ascorbate was required for the reactions leading to lipid peroxidation. Supplementation with aminotriazole (an irreversible inhibitor of the catalase-H2O2 complex) increased chemiluminescence in a time-dependent manner, as catalase reacted with accumulated H2O2, suggesting that ascorbic acid has a dual action being involved in the production of H2O2 and also maintaining Fe in the reduced state to catalyze a Fenton-like reaction. The excited species responsible for the chemiluminescence were partially characterized by adding specific fluorescent energy acceptors: dibromoanthracene (DBA) and diphenylanthracene (DPA). Both DBA and DPA stimulated chemiluminescence several-fold indicating that triplet and singlet species are responsible for the observed chemiluminescence. Excited singlet carbonyls (identified with DPA) may be produced during the collision of two ROO.. Singlet oxygen may also be generated during the same reaction. It decays to the triplet state (emitting chemiluminescence at 634 nm) and reacts with double bonds producing dioxetanes, which may breakdown generating triplet carbonyls (identified with DBA).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Ascorbate- and hemoglobin-dependent brain chemiluminescence. 237 61

Hemorrhage within the central nervous system (CNS) may be associated with subsequent development of seizure states or paralysis. Prior investigations indicate that hemoglobin, released from extravasated erythrocytes, may be toxic to the CNS by promoting peroxidation of lipids and inhibition of Na,K-ATPase. These deleterious effects are blocked both in vitro and in vivo by the Fe3+ chelator, desferrioxamine, indicating the involvement of free iron derived from hemoglobin. We now report that the Fe2+ chelator, ferene, also inhibits methemoglobin- and ferric iron-mediated CNS lipid oxidation, reflecting the reduction of Fe3+ by some component of the CNS. This reduction is apparent in the accumulation of the highly chromophoric ferene: Fe2+ chelate after the addition of Fe3+ salts to supernatants of murine brain homogenates. Because large amounts of ascorbic acid occur in mammalian CNS, we suspected that this reducing substance might be responsible. Indeed, the peroxidative effects of hemoglobin and iron on murine brain are blocked by washing of CNS membranes or by preincubation of crude homogenates with ascorbate oxidase. Furthermore, the addition of ascorbate to washed CNS membranes fully restores hemoglobin/iron-driven peroxidation. We conclude that posthemorrhagic CNS dysfunction may stem from damaging redox reactions between hemoglobin iron, ascorbic acid, and oxidizable components of the nervous system.
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PMID:Hemoglobin-mediated oxidant damage to the central nervous system requires endogenous ascorbate. 284 56

Blue light irradiation of 2-deoxyribose (DOR) in the presence of uroporphyrin I (UP), ascorbate (AH-), trace iron, and phosphate buffer resulted in a strong stimulation of hydroxyl radical (OH.)-dependent oxidation of DOR. Photostimulated generation of H2O2 was monitored after removal of residual AH- (i) by ascorbate oxidase treatment, or (ii) by anion exchange on mini-columns of DEAE-Sephadex. Irradiation of the above mixture produced a strong burst of H2O2 which was intensified by desferrioxamine and suppressed by catalase or EDTA. The mechanism suggested by these observations is one in which photoreduction of UP to the radical anion initiates the formation of H2O2, which gives rise to OH. via Fenton chemistry. This is the first known investigation of H2O2 fluxes in a Type I (free radical) photoreaction involving AH- as the electron donor.
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PMID:Light-stimulated formation of hydrogen peroxide and hydroxyl radical in the presence of uroporphyrin and ascorbate. 285 16

The complexes of NO with CuB of cytochrome c oxidase in which cytochrome a3 may or may not be ligated to cyanide or fluoride are photodissociable. NO does not appear to react with CuB in complexes of cytochrome c oxidase in which sulphide or mercaptans are ligated to the haem iron of cytochrome a3. A comparison is made between the photoreactivity of the complexes of NO with cytochrome c oxidase and those with ceruloplasmin, ascorbate oxidase, and haemocyanin. It is shown that the photoreactivity of CuB 2+.NO in cytochrome c oxidase is not unique for this enzyme, but may also be observed in the complexes of NO with type-1 copper-containing enzymes. This would suggest that the ligation of CuB in cytochrome c oxidase shows some similarity to type-1 copper in blue oxidases.
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PMID:The photoreactivity of the copper-NO complexes in cytochrome c oxidase and in other copper-containing proteins. 299 61

Experiments were carried out to evaluate the production of hydroxyl radical-like species by intact rat liver cells by assaying for the production of ethylene from alpha-keto-4-thiomethylbutyric acid in the absence and presence of added iron. In the absence of iron, a low rate of ethylene production, which was not sensitive to superoxide dismutase, catalase, or competitive scavengers was observed. Ethylene was produced when KMBA was incubated with perfusates of rat liver or the suspension medium obtained after incubating liver cells for varying periods of time, followed by removal of the liver cells. Boiling the perfusate or suspension medium had no effect on ethylene production. This ethylene production does not appear to reflect an oxygen radical-mediated event. The addition of ferric-EDTA, but not ferric-desferrioxamine, increased ethylene production by the hepatocyte suspensions in a reaction sensitive to inhibition by catalase, ascorbate oxidase, and competitive scavengers, but not superoxide dismutase. The sensitivity to externally added catalase and ascorbate oxidase suggested that the ethylene production reflected an extracellular oxygen radical generating system. Ferric alone and several ferric chelates, for example, ferric-ATP, ADP, AMP, histidine, and citrate stimulated ethylene production using perfusates of liver or suspension medium after removal of the hepatocytes. The sensitivity of the added iron system to ascorbate oxidase suggested that during perfusion or incubation of liver cells, efflux of ascorbate occurs, followed by reduction of the iron and subsequently, extracellular production of oxygen radicals.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Ethylene production from alpha-keto-4-thiomethylbutyric acid by isolated rat liver cells, suspension medium, and perfusates in the absence and presence of iron. 301 75

A preliminary study (J.M. Mata, R. Assad, and B. Peterkofsky (1981) Arch. Biochem. Biophys. 206, 93-104) suggested that chick embryo limb bone microsomes took up and concentrated [14C]ascorbate in the presence of cofactors for prolyl hydroxylase. In the present study, we found that the apparent Km for ascorbate in the hydroxylation of intracisternal unhydroxylated procollagen by endogenous prolyl hydroxylase was approximately an order of magnitude less than the value obtained when enzyme solubilized from microsomes was used with an exogenous substrate. These results are compatible with a concentrative uptake of ascorbate into microsomes. The uptake of [14C]ascorbate into microsomes was confirmed and it required only iron, in either the ferrous or ferric form, and was time and temperature dependent, proportional to microsome concentration, and substrate saturable at 2-3 mM ascorbate. Iron-dependent ascorbate uptake also was observed with L-929 cell microsomes. [14C]Ascorbate seemed to be taken up without prior oxidation, since only unlabeled ascorbate, and not dehydroascorbate, competed for uptake into limb bone microsomes. A functional requirement for Fe2+ in ascorbate transport was demonstrated using the intracisternal proline hydroxylating system. L-929 cell microsomes were preincubated with ascorbate with or without the metal and then external ascorbate was oxidized to inactive dehydroascorbate using ascorbic acid oxidase, which cannot penetrate the microsomal membrane. Samples which did not receive iron during the preincubation received it, along with other requirements for prolyl hydroxylase, in a final incubation to measure hydroxylation. Significant hydroxylation was obtained only in samples incubated with iron prior to oxidase treatment, consistent with the conclusion that an iron-dependent process was required to translocate ascorbate and protect it from the oxidase.
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PMID:Iron-dependent uptake of ascorbate into isolated microsomes. 303 60

Addition of alcohol oxidase to erythrocytes treated with ascorbic acid reverses the vitamin C effect, as expressed by the appearance of the semidehydroascorbate signal, and the increase in spin concentration. The original erythrocyte electron spin resonance (ESR) signal is, however, never restored completely, as it is in the case if ascorbate oxidase is used. Additional interaction between the enzyme alcohol oxidase and haemoglobin iron must occur, since both of the iron ESR signals at g = 4.3 and g = 6 disappear and the erythrocyte ESR spectrum at g approximately equal to 2 is changed characteristically. The spin concentration of the latter spectrum increases again above a certain concentration of alcohol oxidase.
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PMID:The effect of alcohol oxidase on the ascorbic acid-erythrocyte interaction: ESR investigations. 631 79

Exposure of human caeruloplasmin, an acute phase protein with antioxidant properties, to a mixture of xanthine/hypoxanthine and xanthine oxidase as a source of reactive oxygen intermediates decreased its ferroxidase and ascorbate oxidase activities and its ability to inhibit lipid peroxidation. Immunological reactivity was also altered. Exposure to hydrogen peroxide mimicked these effects. Exposure to low-intensity u.v. irradiation depressed caeruloplasmin's ability to inhibit iron-catalysed hyaluronic acid degradation. The results may explain the mechanism of the observed inactivation of caeruloplasmin within human rheumatoid synovial fluid.
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PMID:Action of free radical generating systems upon the biological and immunological properties of caeruloplasmin. 654 84


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