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.
|Superclasses:||Degradation/Utilization/Assimilation → Carboxylates Degradation → Oxalate Degradation|
Oxalate is the most oxidized two-carbon compound. It is made in high concentrations by some plants and fungi and can reach high micromolar concentrations in soil. Oxalate is toxic to mammals but is metabolized by many bacteria and plants by various pathways.
Oxalate oxidase, an enzyme that catalyzes the oxidative cleavage of oxalate to carbon dioxide with reduction of dioxygen to hydrogen peroxide, is widespread in cereal plants [Lane02, Lane00, Lane93]. The enzyme has also been described in bacteria [Koyama88] and fungi [Escutia05], although it does not appear to be common in these organisms.
Germin is a hydrogen peroxide generating enzyme found in several plant species, including barley (Hordeum vulgare) and wheat (Triticum aestivum), and some fungi. Germin's synthesis coincides with the onset of growth in germinating wheat embryos (hence the name). The enzyme serves as a marker of embryonic development in germinating wheat grains
The enzyme has been shown to be an oxalate oxidase [Dumas93, Lane93] that is involved in the defense against biotic and abiotic stress in plants [Lane02]. Enzyme activity is detected in barley seedling roots during development and in the leaves of mature plants in response to powdery-mildew infection [Dumas95].
The exact nature of the elevated resistance to pathogens is still not clear, but several hypotheses exist [Lane02]:
(1) generation of microcidal concentrations of hydrogen peroxide
(2) elicitation of hypersensitive cell death at lower concentrations of hydrogen peroxide
(3) formation of effective barriers against predator penetration by the hydrogen-peroxide-mediated lignification of cell walls
(4) destruction of oxalate, which is an inhibitor of the hypersensitive response, a strategy employed byubiquitous predator organisms such as Sclerotinia sclerotiorum, which secretes high concentrations of oxalate as a toxin.
Dumas95: Dumas B, Freyssinet G, Pallett KE (1995). "Tissue-Specific Expression of Germin-Like Oxalate Oxidase during Development and Fungal Infection of Barley Seedlings." Plant Physiol 107(4);1091-1096. PMID: 12228419
Escutia05: Escutia MR, Bowater L, Edwards A, Bottrill AR, Burrell MR, Polanco R, Vicuna R, Bornemann S (2005). "Cloning and sequencing of two Ceriporiopsis subvermispora bicupin oxalate oxidase allelic isoforms: implications for the reaction specificity of oxalate oxidases and decarboxylases." Appl Environ Microbiol 71(7);3608-16. PMID: 16000768
Kotsira97: Kotsira VP, Clonis YD (1997). "Oxalate oxidase from barley roots: purification to homogeneity and study of some molecular, catalytic, and binding properties." Arch Biochem Biophys 340(2);239-49. PMID: 9143327
Woo00: Woo EJ, Dunwell JM, Goodenough PW, Marvier AC, Pickersgill RW (2000). "Germin is a manganese containing homohexamer with oxalate oxidase and superoxide dismutase activities." Nat Struct Biol 7(11);1036-40. PMID: 11062559
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