Dehydroascorbic reductase

Fig. 8. The relationship between leaf water potential (V>l) mono-dehydroascorbate reductase activity in barley leaves during a 7-day drying period, r = 0.72, P<0.001 (from Smirnoff Colombe, 1988).

In contrast, antioxidant enzymes can efficiently counteract all UV-induced ROS (Aguilera et al. 2002). These enzymes are represented by superoxide dismutase (SOD), catalase and glutathione peroxidase as well as those involved in the ascorbate-glutathione cycle, such as ascorbate peroxidase, mono-dehydroascorbate reductase, dehydroascorbate reductase and glutathione reductase. One of the most important classes of antioxidant enzymes is the SOD family, which eliminate noxious superoxide radical anions. Different metalloforms of SOD exist (Fe, Mn, CuZn and Ni), which due to their intracellular localisation protect different cellular proteins (Lesser and Stochaj 1990). 

BOROHYDRIDE REDUCTION DEHYDROASCORBATE REDUCTASE DEHYDROCHOLESTEROL REDUCTASE 2-DEHYDRO-3-DEOXY-D-GLUCONATE... 

AMINO ACID DEHYDROGENASE AQUACOBALAMIN REDUCTASES BENZOATE L,2-DIOXYGENASE BETAINE-ALDEHYDE DEHYDROGENASE CDP-GLUCOSE 4,6-DEHYDRATASE DEHYDROASCORBATE REDUCTASE... 

NICOTINAMIDE COENZYMES (SREC-TRAL PROPERTIES) NADH-dependent enzymes, AQUACOBALAMIN REDUCTASES BENZENE 1,2-DIOXYGENASE DEHYDROASCORBATE REDUCTASE GLUTAMATE SYNTHASE GLYOXYLATE REDUCTASE 3-HYDROXYBENZOATE 6-MONOOXY-GENASE... 

In addition to its function in thiol/disulfide exchange, Grx-1 also serves as an alternative electron donor to ribonucleotide reductase (Fernandes and Holmgren 2004), participates in deiodination of thyroxine to triiodothyronine (Takagi et al. 1989), and acts as a dehydroascorbate reductase for regenerating ascorbic acid (Washburn and Wells 1989). However, despite the potential role of Grx in... 

Figure 13.2. Biosynthesis of ascorbate. Glucuronate reductase, EC 1.1.1.19 glucono-lactone3-lactonase, EC 3.1.1.17 gulonolactone oxidase, EC 1.1.3.8 NADPH-dependent dehydroascorbate reductase, EC 1.6.5.4 and glutathione-dependent dehydroascorbate...

The immediate product of the oxidative reaction, the monodehydroascorbate radical (Eq. [1]), is a fairly reactive and unstable species which, in the presence of a suitable reductase system, is reduced back to ascorbate. Monodehydroascorbate reductases have been identified and purified in a few cases (Ushimara et al., 1997 Dalton et al., 1992 Shigeoka et al., 1987 Borraccino et al., 1986 Hossain et al., 1984) and cDNA sequences have been published for the pea (Murthy and Zilinskas, 1994) and cucumber enzymes (Sano et al., 1995). A bacterial expression system is also available for the cucumber enzyme (Sano et al., 1995). In the absence of a suitably efficient reductase system, the monodehydroascorbate radicals disproportionate to dehydroascorbate and ascorbate in this case, ascorbate is regenerated using a glutathione-dependent dehydroascorbate reductase enzyme (Foyer and Mullineaux, 1998 and references therein). Under non-... 

Foyer, C. H., and Mullineaux, P. M., 1998, The presence of dehydroascorbate and dehydroascorbate reductase in plant tissues, FEBS Lett. 425 5289529. 

Shigeoka, S., Yasumoto, R., Onishi, T., Nakano, Y., and Kitaoka, S., 1987, Properties of mon-odehydroascorbate reductase and dehydroascorbate reductase and their participation in the regeneration of ascorbate in Euglena gracilis, J. Gen. Microbiol. 133 227n232. 

Ushimara, T., Maki, Y., Sano, S., Koshiba, K., Asada, K., and Tsuji, H., 1997, Induction of enzymes involved in the ascorbate-dependent antioxidative systems, namely ascorbate peroxidase, monodehydroascorbate reductase and dehydroascorbate reductase, after exposure to air of rice Oryza sativa) seedlings germinated under water, Plant Cell Physiol. 38 541n549. 

Schmuck, E.M., Board, P.G., Whitbread, A.K., Tetlow, N., Cavanaugh, J.A., Blackburn, A.C., Masoumi, A. (2005). Characterization of the monomethylarsonate reductase and dehydroascorbate reductase activities of Omega class glutathione transferase variants implications for arsenic metabolism and the age-at-onset of Alzheimer s and Parkinson s diseases. Pharmacogenet. Genomics 15 493-501. 

E. Maellaro, B. Del Bello, L. Sugherini, A. Santucci, M. Comporti and A.F. Casini, Purification and characterization of glutathione-dependent dehydroascorbate reductase from rat liver, Biochem. J. 301 (1994) 471-476. 

Spinach leaves contain a dehydroascorbate reductase enzyme that catalyzes Reaction 13 at acidic and neutral pH values, but the enzyme is not, located within the chloroplast (73-76). GSSG produced by Reaction 13 can be re-converted to GSH by glutathione reductase, an enzyme located in the chloroplast (77). 

Abbreviations A, - secondary electron acceptor in rCj AA - ascorbic acid AOS - active oxygen species APX - ascorbate peroxidase Ci-intracellularCOjConcentrations Chi - chlorophyll singlet state DHA-dehydroascorbate DHAR-dehydroascorbate reductase ... 

Fig. 14. The ascorbate-glutathione cycle. APX - ascorbate peroxidase DMA - dehydroascorbate DHAR - dehydroascorbate reductase OR - glutthione reductase GSH - reduced glutathione GSSG - glutathione disulfide MDHR - monodehydroascorbate reductase.

The presence of ascorbate peroxidase (32) in addition to a dehydroascorbate reductase in T. cruzi (91) has led to the suggestion of the occurrence of an enzymatic vitamin C redox cycle that would replenish ascorbic acid for reactive oxygen species removal (91). 

Clarke, D., Albrecht, M. and Arevalo, J. (1994) Ascorbate variations and dehydroascorbate reductase activity in Trypanosoma cruzi epimastigotes and trypomastigotes. Mol. Biochem. Parasitol. 66 143-145. 

The dismutating activity of bound manganese (10) may also be important. The generation of hydrogen peroxide in this reaction may be tolerated by the presence of additional enzyme systems that catalyse the destruction of H2O2 (11) (i) ascorbate peroxidase, (ii) dehydroascorbate reductase, and (iii) glutathione reductase. 

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