Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: DrugBank:EXPT00568 (ascorbate)
 23,072 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Several constituents of serum and related substances were examined in order to find factors influencing ascorbate radical formation. Human ceruloplasmin and albumin catalyzed singly ascorbate oxidation and caused a remarkable increase in ESR intensity of the ascorbate radical. Although, however, the combination of these two factors showed synergic effects on catalysis of ascorbate oxidation, the radical intensity significantly decreased. Fibrinogen and fetuin showed inhibitory effects on catalysis of ascorbate oxidation, whereas transferrin, citric acid, or other related substances exhibited no effect. A new factor which inhibited ascorbate oxidation was found in a serum fraction. These results indicate there is a counterbalanced equilibrium in the redox process of ascorbate in serum and the intensity of ascorbate radical is influenced by the summation of the complicated effects of many factors.
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PMID:Factors influencing ascorbate free radical formation. 399 30

We have synthesized spin-labeled analogues of phosphatidylcholine, phosphatidylserine, and phosphatidylethanolamine with a short beta chain (C5) bearing a doxyl group at the fourth position. When added to an erythrocyte suspension, the labels immediately incorporate in the membrane. The orientation of the spin-labels was assessed in the bilayer (i) by addition in the medium of a nonpermeant reducer (ascorbate at 5 degrees C) or (ii) by following spontaneous reduction at 37 degrees C due to the endogenous reducing agents present in the cytosol. Both techniques prove that the spin-labels are originally incorporated in the outer leaflet and redistribute differently after incubation. After a 5-h incubation at 5 degrees C, the phosphatidylcholine derivative remained in the outer layer, while the phosphatidylethanolamine and phosphatidylserine derivatives were found principally in the inner leaflet. During the incubation, a small fraction of the spin-labels is hydrolyzed, particularly the phosphatidylserine derivative, presumably by an endogenous phospholipase A2. Because the hydrolyzed spin-labeled fatty acids are rejected in the aqueous phase, the spectra of the intact membrane-bound phospholipids can be obtained by an adequate spectral subtraction. The ESR spectrum corresponding to a probe in the outer leaflet indicates a more restricted motion than that associated with probes in the inner leaflet. Additional experiments have been carried out to prove that the difference in viscosity, which is likely to be due to anisotropic cholesterol distribution, is not attributable to modification of the cell morphology.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Asymmetric lipid fluidity in human erythrocyte membrane: new spin-label evidence. 609 44

Using ESR we have demonstrated the formation of the ascorbate free radical from sodium ascorbate, methylene blue and light. In oxygen uptake experiments we have observed the production of hydrogen peroxide while spin trapping experiments have revealed the iron catalyzed production of the hydroxyl free radical in this system. The presence of this highly reactive radical suggests that it could be the radical that initiates free radical damage in this photodynamic system.
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PMID:Hydrogen peroxide and hydroxyl radical formation by methylene blue in the presence of ascorbic acid. 609 84

Injuring light induced structural changes in rod outer segment (ROS) membranes are studied using "ST EST spectroscopy" for spin labelled rhodopsin, ESR of lipid spin label and SDS gel-electrophoresis. Free SH-group content of rhodopsin and lipid peroxidation level were simultaneously determined as well. A decrease of rotational mobility of rhodopsin in ROS induced by prolonged illumination is shown to result from irreversible protein aggregation caused by disulfide bond formation between "hydrophobic" SH-groups of rhodopsin. Some decrease of lipid microviscosity and degree of order are found, in contrast to considerable rise in microviscosity due to Fe2+-ascorbate induced lipid peroxidation of ROS membranes. Lipid oxidation is found to accelerate protein aggregation which in its turn influences the state of lipid bilayer.
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PMID:[Aggregation of rhodopsin molecules during damaging exposure of photoreceptor membranes to light]. 626 56

Selective labeling with N-(1-oxyl-2,2,6,6-tetramethyl-4-piperidinyl)-maleimide of human serum LDL has been performed. The spin-labeled LDL exhibited an ESR spectrum containing signals of a strongly immobilized component only. The signals were completely reversible between 4 degrees C and 37 degrees C and fairly stable at each temperature. The spin-labeled LDL which was prepared by the usual method exhibited an ESR spectrum containing signals of both strongly immobilized and weakly immobilized components (5, 6). The latter was unstable above 25 degrees C and changed irreversibly. The strongly binding site showed higher affinity for the nitroxide radical than the weakly binding site, and two kinds of the strongly binding site were demonstrated kinetically. The rate of binding of the nitroxide radical to the two kinds of strongly binding site were estimated to be 4.7 x 10(4) M-1 . day-1 and 0.16 x 10(4) M-1 . day-1 at pH 7.4 and 4 degrees C, respectively. Both the strongly immobilized and weakly immobilized radicals were reduced with ascorbate at the same rate. It was also shown on gel filtration of the SDS-treated LDL derivatives that the strongly immobilized component was on the apoprotein B moiety, whereas either noncovalent binding to LDL or binding to some small molecular species other than protein was suggested for the weakly immobilized component.
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PMID:A spin label study on human low density lipoprotein. 627 91

A doublet signal was observed in human serum by the ESR technique at room temperature. This radical had a g value of 2.0054 and a hyperfine splitting constant of 1.84 gauss and was assigned to ascorbate radical. The ascorbate radical in serum was very stable. The intensity of ESR signal showed no differences between serum and plasma of the same individual. Photosensitivity of the ascorbate radical in serum and sodium ascorbate solution was examined and enhancement of ESR signal by irradiation was observed, although the responses in serum and in ascorbate solution were considerably different. The intensity of ESR signal was proportional to the concentration of ascorbate solution. The ESR intensity of ascorbate radical can be used as a reliable method for quantitative estimation of ascorbate radical.
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PMID:Nature of serum ascorbate radical and its quantitative estimation. 628 Mar 38

Standard midpoint potentials have been determined for p-benzoquinone, methoxy-p-benzoquinone and 2,3-, 2,5-, and 2,6-dimethoxy-p-benzoquinones in aqueous solution. ESR studies have been made of the ascorbate and semiquinone radicals produced when these quinones interact with sodium ascorbate. Direct correlations are found between the electrochemical potentials, generated semiquinone lifetimes, and cytotoxic action in Ehrlich ascites-bearing mice.
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PMID:Ascorbate-quinone interactions: electrochemical, free radical, and cytotoxic properties. 629 61

ESR spectra of erythrocyte membranes labeled with a maleimide spin label (MSL) show two types of label environment: a weakly immobilized component and a strongly immobilized component. Chlorpromazine (CPZ) markedly altered the spectra: at pH 8.0, 3 mM CPZ reduced the amplitude of the spectrum by 40%, and the weakly immobilized component was almost completely removed. In order to clarify the mechanisms of these spectral changes the protein release from erythrocyte membranes induced by CPZ has been followed. CPZ had a weak solubilizing effect on erythrocyte membranes: less than 1% of the membrane protein was released, mainly Band 6. By comparison with the protein release induced by low-salt treatment it was found that the "detergent-like" property of CPZ cannot explain the alterations in the ESR spectra. The nature of the spectral changes induced by CPZ was different from that of changes induced by lowering the pH to 4.5; correlated with other data this shows that changes in organization or conformation of membrane protein cannot explain the CPZ-induced alterations in the ESR spectra. These spectral changes appeared to be due to the reduction by CPZ of the nitroxide free radical. This was documented by the marked reduction of spin concentration of the labeled ghosts in the presence of CPZ resulting in a decrease in amplitude of the ESR spectrum of MSL-labeled erythrocyte ghosts induced by CPZ. The reduction by CPZ of the nitroxide free radical was compared with that induced by ascorbate. It was found that CPZ preferentially reduces the mobile component of the ESR spectrum of MSL-labeled ghosts. The action of CPZ in reducing free radicals may have consequences for patients receiving long-term treatment with phenothiazine derivatives.
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PMID:Effect of chlorpromazine on proteins in human erythrocyte membranes as inferred from spin labeling and biochemical analyses. 630 35

Pulse radiolysis and electron spin resonance experiments have been performed on the antithrombotic and antimetastatic agent, nafazatrom. Results show that nafazatrom is an extremely reactive scavenger of free radicals. The rate of its reaction with Br-2 is higher than rates found for biologically important antioxidants, tocopherol and ascorbate. The radical formed by oxidation of nafazatrom is indicated by ESR to have a structure similar to phenoxyl radical. This radical is found to decay at a rate approaching diffusion controlled rates. The ease of oxidation of nafazatrom makes it ideally suited to act as an antioxidant. This property may be an important determinant of its pharmacological activities.
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PMID:Reaction of the antithrombotic and antimetastatic agent, nafazatrom, with oxidizing radicals. 631 95

The pH dependence of Fe(III)-amino acid complexes has been studied polarographically and by means of ESR spectroscopy. It could be shown that, at least, two complexes exist: one with a low molecular weight, ESR detectable at acid pH, and one with a high molecular weight at alkaline pH, ESR non detectable. The half wave potential of Fe(III) is lowered by amino acid ligands. The redox interaction of the Fe(III)-amino acid complexes with vitamin C results in a decrease of the ascorbyl radical concentration. Ascorbic acid also forms a complex with Fe(III) as indicated by a polarographic half wave potential near -0.55 V vs. S.C.E. at pH 7.
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PMID:The influence of amino acid ligands and vitamin C on the reduction potential of Fe (III): polarographic and electron spin resonance investigations. 632 6


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