The Edinburgh Cell Wall Group, Institute of Molecular Plant Sciences, The University of Edinburgh, The King's Buildings, Edinburgh EH9 3BF, U.K.
Biochem J. 2018 Nov 9;475(21):3451-3470. doi: 10.1042/BCJ20180688.
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 (HO), 'superoxide' (a ∼50 : 50 mixture of [Formula: see text] and [Formula: see text]), hydroxyl radicals (OH, formed in Fenton mixtures), and illuminated riboflavin (generating singlet oxygen, O). Products were monitored electrophoretically. quenched HO far more effectively than superoxide, but the main products in both cases were 4--oxalyl-l-threonate (4-OxT) and smaller amounts of 3-OxT and OxA + threonate. HO, 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. O had no effect on DHA. was oxidatively decarboxylated by HO, Fenton mixture, and O, forming a newly characterised product, 2-oxo-l--pentonate (OTP; '2-keto-l-xylonate'). Superoxide yielded negligible OTP. Prolonged HO treatment oxidatively decarboxylated OTP to threonate. Oxidation of DKG by HO, Fenton mixture, or O 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 HO and superoxide; DKG more readily by O 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 .
l-抗坏血酸、脱氢 l-抗坏血酸（DHA）和 2,3-二酮基-l-古洛糖酸（DKG）均可清除动植物体内的活性氧（ROS）。在此研究了由此形成的维生素 C 氧化产物。DHA 和 DKG 在 pH 4.7 下与过氧化物（HO）、“超氧自由基”（[Formula: see text]和[Formula: see text]的约 50:50 混合物）、羟基自由基（OH，在 Fenton 混合物中形成）和光照核黄素（产生单线态氧，O）有氧孵育。产物通过电泳监测。HO 比超氧自由基更有效地猝灭，但两种情况下的主要产物都是 4--草酰基-l-苏糖醇（4-OxT）和少量的 3-OxT 和 OxA+苏糖醇。HO，但不是超氧自由基，也产生环状-OxT。稀释的 Fenton 混合物几乎完全氧化了 50 倍过量的 DHA，表明它产生的氧化剂大大超过了理论 OH 产量；它产生草酸盐、苏糖醇和 OxT。O 对 DHA 没有影响。HO、Fenton 混合物和 O 使 DHA 发生氧化脱羧反应，形成一种新的特征产物，2-氧代-l--戊酮酸（OTP；'2-酮-l-木酮酸盐'）。超氧自由基几乎不产生 OTP。HO 长时间处理会将 OTP 氧化脱羧为苏糖醇。HO、Fenton 混合物或 O 氧化 DKG 也会生成痕量的 4-OxT，但检测不到 3-OxT 或环状-OxT。总之，不同的 ROS 攻击 DHA 和 DKG 时会产生不同的氧化产物。DHA 更容易被 HO 和超氧自由基氧化；DKG 更容易被 O 氧化。不同的产物是潜在的信号，使生物体能够对不同的应激做出适当的反应。此外，反应产物的“指纹”在分析上是有用的，它表明哪些 ROS 在起作用。
