Vitamins E and K share structurally related side chains and are degraded to similar final products. For vitamin E the mechanism has been elucidated as initial omega-hydroxylation and subsequent beta-oxidation. For vitamin K the same mechanism can be suggested analogously. omega-Hydroxylation of vitamin E is catalyzed by cytochrome p450 enzymes, which often are induced by their substrates themselves via the activation of the nuclear receptor PXR. Vitamin E is able to induce CYP3A-forms and to activate a PXR-driven reporter gene. It is shown here that K-type vitamins are also able to activate PXR. A ranking showed that compounds with an unsaturated side chain were most effective, as are tocotrienols and menaquinone-4 (vitamin K(2)), which activated the reporter gene 8-10-fold. Vitamers with a saturated side chain, like tocopherols and phylloquinone were less active (2-5-fold activation). From the fact that CYPs commonly responsible for the elimination of xenobiotics are involved in the metabolism of fat-soluble vitamins and the ability of the vitamins to activate PXR it can be concluded that supranutritional amounts of these vitamins might be considered as foreign.

中文翻译：

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维生素E和K的同源代谢和基因激活途径

维生素E和K共享结构上相关的侧链，并降解为相似的最终产品。对于维生素E，其机理已经阐明为最初的ω-羟基化和随后的β-氧化。对于维生素K，可以类似地建议相同的机理。维生素E的ω-羟基氧化作用是由细胞色素p450酶催化的，该酶通常是由其底物本身通过核受体PXR的激活而诱导的。维生素E能够诱导CYP3A形式并激活PXR驱动的报告基因。此处显示，K型维生素也能够激活PXR。排名显示，具有不饱和侧链的化合物，生育三烯酚和甲萘醌4（维生素K（2））最有效，后者激活了8-10倍的报告基因。具有饱和侧链的维生素，诸如生育酚和叶醌的活性较低（活化2-5倍）。从通常负责消除异种生物素的CYP参与脂溶性维生素的代谢以及维生素激活PXR的能力这一事实可以得出结论，这些维生素的超量使用可能被认为是外来的。