Ascorbate oxidation

Phenanthroline, on the other hand, stimulates the activity of some enzymes, perhaps by removing a metal that is inhibitory to the enzyme.523 524 It can induce porphyrin synthesis525 and improve the rate of ascorbate oxidation.526 It induces lysis of sensitized sheep erythrocytes.527 It is reported to reverse the resistance of microorganisms to penicillins.528 It binds to an immunoglobulin.529 It also protects rat liver from injury induced by dimethylnitrosamine530 and ethionine.531... 

Fig. 8.9. Variation of the antioxidant properties of the restructuring care NI-VEA Vital (NIVEA) disposed in a 40 pm layer peak current density (corresponding to ascorbate oxidation) as a function of the time.

Lozinsky, E., Novoselsky, A., Shames, A.I., Saphier O., Likhtenshtein G.., and Meyrstein, D. (2001) Effect of albumin on the kinetic of ascorbate oxidation. Biochim. Biophys. Acta 1526, 53-60. 

Series IV Sites of Inhibitor Action and Ascorbate Oxidation Assay Tube Number ... 

Csala M, Mile V, Benedetti A, Mandl J, Banhegyi G. Ascorbate oxidation is a prerequisite for its transport into rat liver microsomal vesicles. Biochem. J. 2000 349 413-415. 

There is another oxidase present in S. acidocaldarius (DSM 639) [120], a cytochrome aa3 oxidase (a peak at 605 nm). The cytochrome oxidizes horse-heart cytochrome c and TMPD-ascorbate. The ability to oxidize cytochrome c is lost during purification, whereas the oxidation of TMPD-ascorbate increases. The purified cytochrome (Mr 120000) is composed of a single subunit (Mr 38000) and contains two heme molecules as well as two copper atoms per subunit. TMPD-ascorbate oxidation is inhibited by cyanide, sulfide (1-3 mM) and azide (20 mM). The purified enzyme also oxidizes reduced cytochromec but at too slow a rate to be physiologically significant. The absence of cytochrome c in S. acidocaldarius and the loss of the ability to oxidize cytochrome c upon purification indicates this cytochrome is not a cytochrome c oxidase. The cytochrome oxidizes the indigenous quinone found in the membranes, caldariella... 

The current best resolved absorption spectrum of the ascorbate anion radical (Figure 1) was determined (26) in a study of ascorbate oxidation by halide anion radicals (particularly Br2") at pH 11. The spectrum shows a symmetrical Gaussian-type band with an absorption peak at 360 nm and a width at half-maximum of about 50 nm. The molar absorbance at 360 nm = 3300 M cm" is lower than earlier reported values 21,23). 

The work described here on the Cu(II)- and Fe(III)-catalyzed autoxidation of ascorbic acid has been extended to catalytic systems involving vanadyl (12) and uranyl (13) ions. On the basis of the results described above it would seem that there are potentially many other metal ions that are capable of undergoing redox reactions with the ascorbate ion, and that may function as catalysts in the autoxidation of ascorbic acid. Analogous mechanisms may also apply to systems involving metal-ion catalysis of ascorbate oxidation in which the primary oxidant is a reagent other than molecular oxygen. 

Figure 16. Reaction sequence for the dissolution of Fe(III) (hydr)oxides by a reductant such as ascorbate. The fast adsorption of the reductant is followed by steps that involve the electron transfer Fe(III) is reduced to >Fe(II) and ascorbate oxidized to a radical that is desorbed form the surface. The resulting Fe II)—O bond at the surface is more labile than the Fe(III)—O bond. Then Fe(II) becomes detached from the surface and the original surface structure is reconstituted.

Our interest in this copper protein was originally stimulated in 1957 by the possibility that Cp was an animal ascorbate oxidase, an enzyme that had been clearly identified in plants but had eluded detection in animal tissues. Initially there was considerable confusion as to whether the ascorbate oxidate activity of Cp was owing to traces of free Cu(II). We found that the oxidation of ascorbate by Cp and free copper diflFered in so many significant aspects that Cp had an ascorbate oxidase activity... 

Elstner EF, Kramer R. Role of superoxide fi-ee radical ion in phoiosyntheiic ascorbate oxidation and ascorbate-mediated photophosphorylation. Biochimica et Biophysica Acta (BBA) - Bioenergei-... 

Jiang, Q., Lykkesfeldt, J., Shigenaga, M.K., Shigeno, E.T., Christen, S., and Ames, B.N., Gammatocopherol supplementation inhibits protein nitration and ascorbate oxidation in rats with inflammation. Free Radic. Biol. Med., 33,1534,2002. 

Lapenna et al. (1998) found that ticlopidine, a thienopyridine characterised by lipophilic properties, at therapeutically relevant concentrations (2.5-10 pM), but neither aspirin nor salicylate, significantly counteracted copper-driven human LDL oxidation. Ticlopidine, at 5 and 10 pM, was also antioxidant on peroxyl radical-induced LDL oxidation yet it was ineffectual on thiol and ascorbate oxidation mediated by peroxyl radicals themselves, suggesting that drug antioxidant capacity is somehow related to the lipoprotein nature of the oxidiz-able substrate, but not to radical scavenging. The drug could not indeed react with the stable free radical l,l-diphenyl-2-picrylhydrazyl, not had apparent metal complexing-inactivating activity. 

Gonzalez-Reyes et al (1992) have reported that APR induces a quick and permanent plasmalemma hyperpolarization and stimulates the proton efflux in onion roots. Ascorbate and DHA also induce hyperpolarization and acidification of media although their effects are transient. More recently, Gonzalez-Reyes et al (1994a) reported that ascorbate can also stimulate root elongation when culture conditions allow ascorbate to be oxidized in an optimal way to produce APR. On the contrary, inhibition of ascorbate oxidation leads to an inhibition of ascorbate-mediated acceleration of root elongation. 

FIGURE 2. Effect of coenzyme Q on extracellular ascorbate oxidation and growth of K562 cells. ( ), Ascorbate oxidation. CoQ was added to cells in ethanol. After 5 min incubation at 3TC the supernatant was discarded by centrifugation. 2.5 x 10 cells were then resuspended in buffer for the ascorbate stabilization assay (Alcam et ai, 1991). ( ), Cell growth. CoQ-supplemented K562 cells were counted after 48 hr growing in serum-free media. 

Minetti, M., Forte, T, Soriani, M., Quaresima, V., Menditto, A., and Ferrari, M., 1992, Iron-induced ascorbate oxidation in plasma as monitored by ascorbate free radical formation, Biochem. J. 282 459-465. 

Buettner, G. R., 1986, Ascorbate oxidation in the presence of iron and copper chelates, Free Rad. Res. Commun. 1 349-353. 

Nagaraj, R. H., Sell, D. R., Prabhakaram, M., and Ortwerth, B. J., 1991, High correlation between pentosidine protein cross-links and pigmentation implicates ascorbate oxidation in human lens senescence and cataractogenesis, Proc. Natl. Acad. Sci. USA 88 10257-10261. 

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