Laboratory of Chemical Toxicology and Environmental Health, Showa Pharmaceutical University, 3-3165 Higashi-Tamagawagakuen, Machida, Tokyo 194-8543, Japan.
Metallomics. 2013 May;5(5):429-36. doi: 10.1039/c2mt20187a. Epub 2013 Jan 25.
Many studies have examined the metabolic pathway of selenium (Se) compounds in Se-accumulating plants (hereafter "Se accumulators") when the plants are exposed to inorganic Se, such as selenite and selenate. However, if we were to consider Se circulation in the biosphere, the metabolism of organic Se, in particular, selenometabolites of animals and plants, in plants should be elucidated. In this study, Brassica rapa var. peruviridis, a known Se accumulator, was hydroponically cultivated and then exposed to selenometabolites of animals and plants, such as methyl-2-acetamido-2-deoxy-1-seleno-β-d-galactopyranoside (selenosugar, SeSug), trimethylselenonium (TMSe), selenomethionine (SeMet), and Se-methylselenocysteine (MeSeCys). Then, the metabolic pathway of the organic Se compounds/selenometabolites in B. rapa var. peruviridis was investigated by speciation analysis. Two selenometabolites were detected in the roots when the plant was exposed to SeMet, MeSeCys, and SeSug. They were assigned to S-(methylseleno)-glutathione and MeSeCys using electrospray tandem mass spectrometry (ESI-MS-MS) and HPLC-inductively coupled plasma mass spectrometry (ICP-MS). Contrary to SeMet, MeSeCys, and SeSug, TMSe was not metabolized even if it was more efficiently incorporated into the roots than the other Se compounds. The identified metabolites enabled us to propose a metabolic pathway for the organic Se metabolites except TMSe in the plant roots: a monomethylseleno moiety (CH3Se-) commonly existing in SeMet, MeSeCys, and SeSug was cleaved off and conjugated with GSH, and then the CH3Se group was transferred to O-acetylserine to form MeSeCys.
许多研究都考察了在向富硒植物（以下简称“硒积累植物”）中施加无机硒（如亚硒酸盐和硒酸盐）时硒化合物的代谢途径。然而，如果我们要考虑硒在生物圈中的循环，就应该阐明植物中有机硒的代谢，特别是动物和植物的硒代谢物。在这项研究中，白菜型油菜（Brassica rapa var. peruviridis）作为一种已知的硒积累植物，在水培条件下进行培养，然后暴露于动物和植物的硒代谢物，如甲基-2-乙酰氨基-2-脱氧-1-硒-β-D-半乳糖吡喃糖苷（硒糖，SeSug）、三甲基硒（TMSe）、硒代蛋氨酸（SeMet）和硒代蛋氨酸（MeSeCys）。然后，通过形态分析研究了有机硒化合物/硒代谢物在白菜型油菜中的代谢途径。当植物暴露于 SeMet、MeSeCys 和 SeSug 时，在根中检测到两种硒代谢物。它们通过电喷雾串联质谱（ESI-MS-MS）和高效液相色谱-电感耦合等离子体质谱（HPLC-ICP-MS）被分配为 S-（甲基硒代）-谷胱甘肽和 MeSeCys。与 SeMet、MeSeCys 和 SeSug 相反，即使 TMSe 比其他硒化合物更有效地被植物根系吸收，它也不会被代谢。鉴定出的代谢物使我们能够提出植物根系中除 TMSe 以外的有机硒代谢物的代谢途径：普遍存在于 SeMet、MeSeCys 和 SeSug 中的单甲基硒基（CH3Se-）被切断并与 GSH 结合，然后 CH3Se 基团被转移到 O-乙酰丝氨酸以形成 MeSeCys。
