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PubMed · 10905713

Dehydroascorbic acid.

J C Deutsch
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Abstract

Dehydroascorbic acid (DHA) is an important, interesting but somewhat enigmatic compound in biological systems. DHA has many unique properties that set it apart from ascorbic acid (AA), and DHA has functions that may be very important beyond that in the AA:DHA cycle. Future studies should help to better clarify chemical activity of DHA and related products that form from DHA, as well as to highlight the role DHA plays in normal cellular homeostasis.

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BibTeXRIS

J C Deutsch. 2000-06-09. Dehydroascorbic acid.. https://doi.org/10.1016/s0021-9673(00)00166-7

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PubMed2000

Chemical characteristics of dehydro-L-ascorbic acid.

Dehydro-L-ascorbic acid (DAA) exists mainly in its C2 hydrated bicyclic form (5) in an aqueous solution, and monocyclic DAA (3), which is the expected reaction product immediately after the oxidation of AA, has not been observed by NMR spectroscopy. The formation mechanism for 5 from 3 and the stability of 5 were examined by the semi-empirical molecular orbital method (MOPAC). It was indicated that the protonation reaction was the key step in the formation of 5, therefore, the formation of 5 is thought to be more difficult under physiological conditions which mostly involve in the neutral or slightly alkaline state. However, by NMR, it was confirmed that, even in a neutral or slightly alkaline state very close to physiological conditions, the predominant form of DAA existing in an aqueous solution immediately after the enzymatic oxidation of AA was confirmed to be 5, although the possible existence of other forms of DAA at very low concentrations could not be completely excluded.

Dehydroascorbic Acid↗
PubMed1997

Dehydroascorbate and dehydroascorbate reductase are phantom indicators of oxidative stress in plants.

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.

Dehydroascorbic Acid↗