Ascorbate peroxidases

Yan J. Wang J. Tissue D. Holaday A. S. Allen R. Zhang H. (2003) Protection of photosynthesis and seed production under water-deficit conditions in transgenic tobacco plants that over-express Arabidopsis ascorbate peroxidase // Grop Sci. V. 43. P. 1477-483. 

II. Ascorbate Peroxidase (EC 1.11.1.11) APX isoenzyme, plays an important role in the metabolism of H202 in higher plants. APX utilizes Ascorbate (Asx) as its specific electron donor to reduce H202 to water with the generation of monodehydroascorbate, involved in the Ascorbate-GSH cycle. Thus, APX in combination with the effective Asx-GSH cycle functions to prevent the accumulation of toxic levels of H202. 

Observations Table 1 shows the activity of the antioxidant enzymes of tomato roots after 72 h of exposure of allelochemical stress caused by S. deppei. Catalase (CAT) activity increases by 1.5 fold Ascorbate Peroxidase (APX) decreases 2.3 fold Glutathione reductase (GR) activity does not change with the treatment and Superoxide dismutase (SOD) decreases 1.3 fold. 

Procedure The Ascorbate peroxidase (EC 1.11.1.7) activity can be obtained by measuring the oxidation of ascorbate in the presence of H202. Grind the algal sample in liquid nitrogen and extract in 2.5 ml 50 mM potassium phosphate buffer (pH 7.0) containing 10% (w/v)... 

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). 

APX, ascorbate peroxidase PJiP, Arthromyces ramosus peroxidase BPl, barley grain peroxidase CCP, C3dochrome c peroxidase CIP, Coprinus cinereus peroxidase EXAFS, extended X-ray absorption fine structure HRP, horseradish peroxidase HRP Z (where Z = A1-A3, B1-B3, Cl, C2, D, E1-E6, or N), a specific isoenzyme of horseradish peroxidase HS, high-spin lAA, indole-3-acetic acid LIP, hgnin peroxidase LS, low-spin PNP, the major cationic isoenzyme of peanut peroxidase WT, wild-type 5-c, five-coordinate 6-c, six-coordinate. 

Barros M.P., M. Granbom, P. Colepicolo, and M. Pedersen (2003). Temporal mismatch between induction of superoxide dismutase and ascorbate peroxidase correlates with high... 

In plants, ascorbate is required as a substrate for the enzyme ascorbate peroxidase, which converts H202 to water. The peroxide is generated from the 02 produced in photosynthesis, an unavoidable consequence of generating 02 in a compartment laden with powerful oxidation-reduction systems (Chapter 19). Ascorbate is a also a precursor of oxalate and tartrate in plants, and is involved in the hydroxylation of Pro residues in cell wall proteins called extensins. Ascorbate is found in all subcellular compartments of plants, at concentrations of 2 to 25 mM—which is why plants are such good sources of vitamin C. 

Value at initial stage of culture Average APx activity in plant materials Amount of Chi on culture volume basis Average GPx activity in plant materials Average POD activity in plant materials Ascorbate peroxidase... 

Ascorbate Peroxidases, Cytochrome c Peroxidases, and Their Putative Hybrid Types... 

Sharp KH, Mewies M, Moody PC et al (2003) Crystal structure of the ascorbate peroxidase-ascorbate complex. Nat Struct Biol 10 303-307... 

Jensen GM, Bunte SW, Warshel A et al (1998) Energetics of cation radical formation at the proximal active site tryptophan of cytochrome c peroxidase and ascorbate peroxidase. J Phys Chem B 102 8221-8228... 

The third covalent bond present in MPO is also thought to form by an autocatalytic process, although it has not been clearly demonstrated to do so. However, incubation of an ascorbate peroxidase mutant into which a methionine has been introduced by mutagenesis has been shown to result in covalent attachment of the Met sulfur atom to a heme vinyl group [54]. Although the link is not identical to that in MPO, this finding provides strong circumstantial evidence that the bond in MPO is also formed by an autocatalytic mechanism. 

Metcalfe CL, Ott M, Patel N et al (2004) Autocatalytic formation of green heme evidence for H202-dependent formation of a covalent methionine-heme linkage in ascorbate peroxidase. J Am Chem Soc 126 16242-16248... 

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