Innovative Research & Development Laboratory of TCM of Guangdong Province, University of Chinese Medicine, Guangzhou 510006, China.
School of Chinese Herbal Medicine; Guangzhou University of Chinese Medicine, Guangzhou 510006, China.
Molecules. 2019 Jul 30;24(15):2769. doi: 10.3390/molecules24152769.
The biological process, 3--galactosylation, is important in plant cells. To understand the mechanism of the reduction of flavonol antioxidative activity by 3--galactosylation, myricetin-3--galactoside (M3OGa) and myricetin aglycone were each incubated with 2 mol α,α-diphenyl-β-picrylhydrazyl radical (DPPH) and subsequently comparatively analyzed for radical adduct formation (RAF) products using ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UPLC-ESI-Q-TOF-MS) technology. The analyses revealed that M3OGa afforded an M3OGa-DPPH adduct (/ 873.1573) and an M3OGa-M3OGa dimer (/ 958.1620). Similarly, myricetin yielded a myricetin-DPPH adduct (/ 711.1039) and a myricetin-myricetin dimer (/ 634.0544). Subsequently, M3OGa and myricetin were compared using three redox-dependent antioxidant analyses, including DPPH-trapping analysis, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide radical (PTIO)-trapping analysis, and O inhibition analysis. In the three analyses, M3OGa always possessed higher IC values than those of myricetin. Conclusively, M3OGa and its myricetin aglycone could trap the free radical via a chain reaction comprising of a propagation step and a termination step. At the propagation step, both M3OGa and myricetin could trap radicals through redox-dependent antioxidant pathways. The 3--galactosylation process, however, could limit these pathways; thus, M3OGa is an inferior antioxidant compared to its myricetin aglycone. Nevertheless, 3--galactosylation has a negligible effect on the termination step. This 3--galactosylation effect has provided novel evidence that the difference in the antioxidative activities of phytophenols exists at the propagation step rather than the termination step.
3--半乳糖基化是植物细胞中的一个重要的生物过程。为了了解黄酮醇抗氧化活性被 3--半乳糖基化降低的机制，我们分别用 2molα,α-二苯基-β-苦基肼自由基（DPPH）孵育鼠李素-3--半乳糖苷（M3OGa）和鼠李素苷元，然后使用超高效液相色谱-电喷雾电离四极杆飞行时间串联质谱（UPLC-ESI-Q-TOF-MS）技术比较分析自由基加合物形成（RAF）产物。分析表明，M3OGa 生成了 M3OGa-DPPH 加合物（/873.1573）和 M3OGa-M3OGa 二聚体（/958.1620）。同样，鼠李素生成了鼠李素-DPPH 加合物（/711.1039）和鼠李素-鼠李素二聚体（/634.0544）。随后，我们使用三种依赖于氧化还原的抗氧化分析方法比较了 M3OGa 和鼠李素，包括 DPPH 捕获分析、2-苯基-4,4,5,5-四甲基咪唑啉-1-氧自由基（PTIO）捕获分析和 O 抑制分析。在这三种分析中，M3OGa 的 IC 值总是高于鼠李素的 IC 值。结论是，M3OGa 及其鼠李素苷元可以通过一个包含传播步骤和终止步骤的链式反应来捕获自由基。在传播步骤中，M3OGa 和鼠李素都可以通过依赖于氧化还原的抗氧化途径来捕获自由基。然而，3--半乳糖基化过程可以限制这些途径；因此，M3OGa 作为抗氧化剂不如其鼠李素苷元。不过，3--半乳糖基化对终止步骤的影响可以忽略不计。这种 3--半乳糖基化的作用为植物酚类抗氧化活性的差异存在于传播步骤而不是终止步骤提供了新的证据。
