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PubMed · 9563528

Dehydroascorbate reduction: the phantom remaining.

S Morell·H Follmann·M de Tullio·I Häberlein
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Dehydroascorbic AcidGlutathioneOxidation-ReductionOxidative StressOxidoreductasesPlant ProteinsPlantsThioredoxinsJournal Article

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S Morell, H Follmann, M de Tullio, I Häberlein. 1998-04-03. Dehydroascorbate reduction: the phantom remaining.. https://doi.org/10.1016/s0014-5793(98)00282-8

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In many physiological studies dehydroascorbate (DHA) reductase is regarded as one of the chloroplast enzymes involved in the protection against oxidative stress. Here, evidence is presented that plant cells do not possess a specific DHA reductase. The DHA reductase activities measured in plant extracts are due to side reactions of proteins containing redox-active dicysteine sites. Native gel electrophoresis combined with specific activity staining revealed three different proteins with DHA reductase activity in leaf and chloroplast extracts. These proteins have been identified as thioredoxins and trypsin inhibitors (Kunitz type) by Western blot analysis. The essential regulatory functions of thioredoxins in chloroplast metabolism are strongly inhibited in the presence of as little as 50 microM DHA. Thus, the intracellular DHA concentration should be kept below 50 microM but not all proteins with DHA reductase activity are effective enough for this purpose. A specific DHA reductase is frequently demanded as part of the enzymatic equipment to avoid oxidative stress. We argue that this is not necessary because in chloroplasts DHA does not accumulate to any significant extent due to the high activities of monodehydroascorbate reductase and of reduced ferredoxin.

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pH optimum of the reduction of dehydroascorbic acid by dithioerytritol.

Ascorbic acid is a water soluble antioxidant, that is itself oxidized to dehydroascorbic acid. In order to detect dehydroascorbic acid by amperometri it has to be reduced to ascorbic acid beforehand. This reduction was performed with dithioerytritol at pH = 6.0 for 10 min, which is a choice between optimal reaction rate and stability of ascorbic acid. The limit of detection of ascorbic acid is 1.1 pmol making the assay useful for determination of ascorbic and dehydroascorbic acid in small tissue biopsies. Results of this method and a colorimetric method were comparable.

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PubMed1992

Mode of formation of quinoxaline versus 2[1H]-quinoxalinone rings from dehydro-D-erythorbic acid.

The mode of formation of the quinoxaline versus 2[1H]-quinoxalinone rings by the reaction of o-diamines with dehydro-D-erythorbic acid has been investigated. The study was carried out by using one and two molar equivalents of 1,2-diamino-4,5-dimethylbenzene (3b) to give 6,7-dimethyl-3-(1-oxo-D-erythro-2,3,4-trihydroxybutyl)-2[1H]-quino xalinone (4b) and 2-(2-amino-4,5-dimethylphenylcarbamoyl)-3-(D-erythro-glycerol-1-yl )- 6,7-dimethylquinoxaline (6), respectively. The former product exists predominantly as the two furanosyl anomers. Sequential reaction of 4a with 3b has been studied, and the location of each diamine in the product was deduced by using 1H-n.m.r. spectroscopy. A mechanism for the reaction is proposed. Acetate and acetal derivatives of the compound are prepared.

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