This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Synonyms: hydrogen peroxide detoxification
Many metabolic processes, including respiration, photosynthetic electron transport and oxidation of glycolate in photorespiration, generate reactive oxygen species such as singleton oxygen and hydrogen peroxide. For example, the univalent reduction of dioxygen in illuminated chloroplasts produces superoxide anion radicals, which are disproportionate to hydrogen peroxide and dioxygen by the superoxide dismutase enzyme, contained in the stroma and lumen. These highly reactive compounds can damage membrane lipids and certain enzymes and thus interrupt cell function.
The ascorbate-glutathione cycle performs the scavenging of hydrogen peroxide. In this cycle, L-ascorbate and glutathione transfer reducing power from NADPH to hydrogen peroxide, reducing it to water. The reduction of hydrogen peroxide is catalyzed by L-ascorbate peroxidase (cytosolic), in a reaction that generates monodehydroascorbate radical, a radical that can be reduced to ascorbate by monodehydroascorbate reductase. If not reduced rapidly, monodehydroascorbate is disproportionated into L-ascorbate and L-dehydro-ascorbate, and the latter is reduced back to L-ascorbate by dehydroascorbate reductase using glutathione as the reducing agent. The oxidized glutathione is reduced by glutathione reductase using NADPH (see glutathione-glutaredoxin redox reactions).
The ascorbate-glutathione cycle presents in at least four different subcellular locations including the cytosol, chloroplast, mitochondrion and peroxisome. Studies of the Arabidopsis enzymes of the pathway show that the same set of enzymes, including L-ascorbate peroxidase (cytosolic), monodehydroascorbate reductase and glutathione reductase, are dual targeted to chloroplast and mitochondrion [Chew03]. Ascorbate peroxidase is in fact the major peroxidase in spinach leaves.
A similar scavenging system appears to operate in several species of cyanobacteria and Euglena.
Unification Links: AraCyc:PWY-2261
Chew03: Chew O, Whelan J, Millar AH (2003). "Molecular definition of the ascorbate-glutathione cycle in Arabidopsis mitochondria reveals dual targeting of antioxidant defenses in plants." J Biol Chem 278(47);46869-77. PMID: 12954611
Jimenez97: Jimenez A, Hernandez JA, Del Rio LA, Sevilla F (1997). "Evidence for the Presence of the Ascorbate-Glutathione Cycle in Mitochondria and Peroxisomes of Pea Leaves." Plant Physiol 114(1);275-284. PMID: 12223704
Shigeoka02: Shigeoka S, Ishikawa T, Tamoi M, Miyagawa Y, Takeda T, Yabuta Y, Yoshimura K (2002). "Regulation and function of ascorbate peroxidase isoenzymes." J Exp Bot 53(372);1305-19. PMID: 11997377
Board00: Board PG, Coggan M, Chelvanayagam G, Easteal S, Jermiin LS, Schulte GK, Danley DE, Hoth LR, Griffor MC, Kamath AV, Rosner MH, Chrunyk BA, Perregaux DE, Gabel CA, Geoghegan KF, Pandit J (2000). "Identification, characterization, and crystal structure of the Omega class glutathione transferases." J Biol Chem 275(32);24798-806. PMID: 10783391
Ishikawa96: Ishikawa T, Sakai K, Yoshimura K, Takeda T, Shigeoka S (1996). "cDNAs encoding spinach stromal and thylakoid-bound ascorbate peroxidase, differing in the presence or absence of their 3'-coding regions." FEBS Lett 384(3);289-93. PMID: 8617374
Ishikawa98a: Ishikawa T, Yoshimura K, Sakai K, Tamoi M, Takeda T, Shigeoka S (1998). "Molecular characterization and physiological role of a glyoxysome-bound ascorbate peroxidase from spinach." Plant Cell Physiol 39(1);23-34. PMID: 9516999
Leonardis00: Leonardis, Silvana, Dipierro, Nunzio, Dipierro, Silvio "Purification and characterization of an ascorbate peroxidase from potato tuber mitochondria." Plant Physiology and Biochemistry, 2000, 38(10):773-779.
Macdonald06: Macdonald IK, Badyal SK, Ghamsari L, Moody PC, Raven EL (2006). "Interaction of ascorbate peroxidase with substrates: a mechanistic and structural analysis." Biochemistry 45(25);7808-17. PMID: 16784232
Nakano87: Nakano, Y, Asada, K. (1987). "Purification of Ascorbate Peroxidase in Spinach Chloroplasts; Its Inactivation in Ascorbate-Depleted Medium and Reactivation by Monodehydroascorbate Radical." Pl. Cell Physiol. 28:131-140.
Sano95: Sano S, Miyake C, Mikami B, Asada K (1995). "Molecular characterization of monodehydroascorbate radical reductase from cucumber highly expressed in Escherichia coli." J Biol Chem 270(36);21354-61. PMID: 7545669
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