The oxidation of dehydroascorbic acid and 2,3-diketogulonate by distinct reactive oxygen species

Abstract

l-Ascorbate, dehydro-l-ascorbic acid (DHA), and 2,3-diketo-l-gulonate (DKG) can all quench reactive oxygen species (ROS) in plants and animals. The vitamin C oxidation products thereby formed are investigated here. DHA and DKG were incubated aerobically at pH 4.7 with peroxide (H2O2), ‘superoxide’ (a ∼50 : 50 mixture of and ), hydroxyl radicals (•OH, formed in Fenton mixtures), and illuminated riboflavin (generating singlet oxygen, 1O2). Products were monitored electrophoretically. DHA quenched H2O2 far more effectively than superoxide, but the main products in both cases were 4-O-oxalyl-l-threonate (4-OxT) and smaller amounts of 3-OxT and OxA + threonate. H2O2, but not superoxide, also yielded cyclic-OxT. Dilute Fenton mixture almost completely oxidised a 50-fold excess of DHA, indicating that it generated oxidant(s) greatly exceeding the theoretical •OH yield; it yielded oxalate, threonate, and OxT. 1O2 had no effect on DHA. DKG was oxidatively decarboxylated by H2O2, Fenton mixture, and 1O2, forming a newly characterised product, 2-oxo-l-threo-pentonate (OTP; ‘2-keto-l-xylonate’). Superoxide yielded negligible OTP. Prolonged H2O2 treatment oxidatively decarboxylated OTP to threonate. Oxidation of DKG by H2O2, Fenton mixture, or 1O2 also gave traces of 4-OxT but no detectable 3-OxT or cyclic-OxT. In conclusion, DHA and DKG yield different oxidation products when attacked by different ROS. DHA is more readily oxidised by H2O2 and superoxide; DKG more readily by 1O2. The diverse products are potential signals, enabling organisms to respond appropriately to diverse stresses. Also, the reaction-product ‘fingerprints’ are analytically useful, indicating which ROS are acting in vivo.

Effect of Different Methods of Thermal Treatment on Starch and Bioactive Compounds of Potato

“…Proportion of the oxidised form of DHAA in tubers following thermal treatment, similarly to its proportion in raw tubers, was small and ranged from 1.2% (microwaving) to 2.7% (boiling). Literature shows, that depending on the conditions, ascorbic acid, besides being oxidised to the dehydro form (DHAA), may also undergo oxidative decomposition into oxalic acid and L-threonic acid [25]. Our results are comparable with the results of Jimenez et al [14].…”

Metabolomic analysis of date palm seedlings exposed to salinity and silicon treatments

“…All three forms have been shown to have antioxidant properties. 76 It was also suggested that the catabolism of ascorbic acid correlates with the rate of cell expansion, 77 and that the metabolites of 2,3-diketo-L-gulonate play a role in pathogen defense. 78 Date palm seedlings treated with silicon and grown under control conditions also accumulated plant biotic defense metabolites such as the antifungal aromatic anofinic acid, 79 the broad-spectrum antifungal agent glucoraphanin 80 and the jasmonic acid derivative epi-4ʹ-hydroxyjasmonic acid.…”

Ascorbate Oxidase Induces Systemic Resistance in Sugar Beet Against Cyst Nematode Heterodera schachtii

“…In the apoplast, reduced AA concentration is lower while the oxidized form of AA, dehydroascorbate (DHA), is more predominant than in the symplast (Smirnoff and Arnaud, 2019). The breakdown of DHA results in the formation of derivatives, such as oxalic, threonic acid and 2,3-L-diketogulonate in the apoplast (Dewhirst and Fry, 2018), which leads to generation of H 2 O 2 that could play a role in defense signaling (Smirnoff, 2018). AO was shown to play a role in cell growth (De Tullio et al, 2013) and work on transgenic AO overexpression lines demonstrated that AO plays a role in stress tolerance (Yamamoto et al, 2005;Pignocchi et al, 2006;Garchery et al, 2013;Karpinska et al, 2018).…”