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

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 (H 2 O 2 ), ‘superoxide’ (a ∼50 : 50 mixture of O 2 ⋅ − and H O 2 ⋅ ), hydroxyl radicals ( • OH, formed in Fenton mixtures), and illuminated riboflavin (generating singlet oxygen, 1 O 2 ). Products were monitored electrophoretically. DHA quenched H 2 O 2 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. H 2 O 2 , 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. 1 O 2 had no effect on DHA. DKG was oxidatively decarboxylated by H 2 O 2 , Fenton mixture, and 1 O 2 , forming a newly characterised product, 2-oxo-l- threo -pentonate (OTP; ‘2-keto-l-xylonate’). Superoxide yielded negligible OTP. Prolonged H 2 O 2 treatment oxidatively decarboxylated OTP to threonate. Oxidation of DKG by H 2 O 2 , Fenton mixture, or 1 O 2 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 H 2 O 2 and superoxide; DKG more readily by 1 O 2 . 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 .