中文名称 | 英文名称 | CAS号 | 化学式 | 分子量 |
---|---|---|---|---|
—— | 2,5-bis(methoxymethoxy)-1-methyl-3-<(E,E,E)-3,7,11,15-tetramethylhexadeca-2,6,10,14-tetraenyl>benzene | 50848-62-9 | C31H48O4 | 484.72 |
中文名称 | 英文名称 | CAS号 | 化学式 | 分子量 |
---|---|---|---|---|
—— | 2,3-Dimethyl-6-geranylgeranyl-1,4-benzoquinol | —— | C28H42O2 | 410.64 |
—— | 2-(geranylgeranyl)-6-methyl-1,4-benzohydroquinone diacetate | 75558-34-8 | C31H44O4 | 480.688 |
Tocopherols are lipophilic antioxidants synthesized exclusively by photosynthetic organisms and collectively constitute vitamin E, an essential nutrient for both humans and animals. Tocopherol cyclase (TC) catalyzes the conversion of various phytyl quinol pathway intermediates to their corresponding tocopherols through the formation of the chromanol ring. Herein, the molecular and biochemical characterization of TCs from Arabidopsis (VTE1 [VITAMIN E 1]), Zea mays (SXD1 [Sucrose Export Deficient 1]) and Synechocystis sp. PCC6803 (slr1737) are described. Mutations in the VTE1, SXD1, or slr1737 genes resulted in both tocopherol deficiency and the accumulation of 2,3-dimethyl-6-phytyl-1,4-benzoquinone (DMPBQ), a TC substrate. Recombinant SXD1 and VTE1 proteins are able to convert DMPBQ to γ-tocopherol in vitro. In addition, expression of maize SXD1 in a Synechocystis sp. PCC6803 slr1737 knockout mutant restored tocopherol synthesis, indicating that TC activity is evolutionarily conserved between plants and cyanobacteria. Sequence analysis identified a highly conserved 30-amino acid C-terminal domain in plant TCs that is absent from cyanobacterial orthologs. vte1-2 causes a truncation within this C-terminal domain, and the resulting mutant phenotype suggests that this domain is necessary for TC activity in plants. The defective export of Suc in sxd1 suggests that in addition to presumed antioxidant activities, tocopherols or tocopherol breakdown products also function as signal transduction molecules, or, alternatively, the DMPBQ that accumulates in sxd1 disrupts signaling required for efficient Suc export in maize.
生物合成的脂溶性抗氧化剂生育酚仅由光合生物合成,共同构成维生素E,是人类和动物的必需营养素。生育酚环化酶(TC)通过形成色酚环催化各种植物醌途径中间体的转化为相应的生育酚。本文描述了来自拟南芥(VTE1 [维生素E 1])、玉米(SXD1 [蔗糖导出缺陷1])和Synechocystis sp. PCC6803(slr1737)的TC的分子和生化特性。VTE1、SXD1或slr1737基因的突变导致生育酚缺乏和2,3-二甲基-6-植酰基-1,4-苯醌(DMPBQ)的积累,这是TC底物。重组的SXD1和VTE1蛋白能够在体外将DMPBQ转化为γ-生育酚。此外,将玉米SXD1在Synechocystis sp. PCC6803 slr1737敲除突变体中表达可恢复生育酚合成,表明植物和蓝细菌之间的TC活性在进化上是保守的。序列分析确定了植物TC中高度保守的30个氨基酸C端结构域,而蓝细菌同源物中则不存在。vte1-2导致该C端结构域的截短,导致的突变表型表明该结构域对于植物中的TC活性是必需的。sxd1中的蔗糖缺陷表明,除了预期的抗氧化活性外,生育酚或生育酚降解产物还起到信号转导分子的作用,或者是sxd1中积累的DMPBQ干扰了玉米高效蔗糖导出所需的信号传递。
The biosynthesis of the tocotrienol and tocopherol forms of vitamin E is initiated by prenylation of homogentisate. Geranylgeranyl diphosphate (GGDP) is the prenyl donor for tocotrienol synthesis, whereas phytyl diphosphate (PDP) is the prenyl donor for tocopherol synthesis. We have previously shown that tocotrienol synthesis is initiated in monocot seeds by homogentisate geranylgeranyl transferase (HGGT). This enzyme is related to homogentisate phytyltransferase (HPT), which catalyzes the prenylation step in tocopherol synthesis. Here we show that monocot HGGT is localized in the plastid and expressed primarily in seed endosperm. Despite the close structural relationship of monocot HGGT and HPT, these enzymes were found to have distinct substrate specificities. Barley (
Tocopherol (vitamin E) is a plant chloroplast lipid presumed to be involved in the response to oxidative stress. A tocopherol-deficient mutant (