生育三烯酚的生理功能及合成代谢调控

维生素E是一种重要的脂溶性抗氧化剂。天然维生素E包括α-、β-、γ-和δ-生育酚及α-、β-、γ-和δ-生育三烯酚等8种组分。生育三烯酚具有独特的降低胆固醇、抗癌和神经保护功能,这些功能是生育酚所不具备的。生育三烯酚主要由谷物等单子叶植物合成。虽然生育三烯酚成分占天然维生素E的一半,但有关生育三烯酚的研究仅占维生素E全部文献的1%。可喜的是,近年来这一领域的研究取得了较大的进展。我们就生育三烯酚在人体内的生理功能、来源、生物合成及代谢调控等方面的进展进行概述。     

植物维生素E合成相关酶基因的克隆及其在体内功能研究进展

维生素E（VE）的天然产物有8种类型,分别为α、β、γ、δ-生育酚（tocopherol）和α、β、γ、δ-生育三烯酚（tocotrienol）,对植物、动物和人类都具有十分重要的生理作用。医学证明,维生素E不仅与生殖系统,而且与中枢神经系统、消化系统、心血管系统和肌肉系统的正常代谢都有密切关系;它也是治疗冠心病、动脉粥样硬化、贫血、脑软化、肝病和癌症等的辅助药物。而绿色植物则是人类和动物VE的基本来源。近年来随着植物基因组学的发展和营养基因组学概念的提出,通过快速分离植物营养代谢（VE）相关酶的基因,最终解析和调控植物微量营养素代谢途径,利用代谢工程的方法大大提高植物营养价值之策略正在逐步完善。本文对有关植物中VE生物合成途径和相关酶基因克隆研究现状,以及VE在植物体内的作用和功能研究进展进行了综述,以期为VE作用机理的探寻和功能开发提供新思路。     

植物VE合成相关酶基因克隆及VE在体内功能研究进展

维生素E(VE)的天然产物有8种类型, 分别为a、b、g、d-生育酚(tocopherol)和a、b、g、d-生育三烯酚(tocotrienol), 对植物、动物和人类都具有十分重要的生理作用。医学证明, 维生素E不仅与生殖系统,而且与中枢神经系统、消化系统、心血管系统和肌肉系统的正常代谢都有密切关系; 它也是治疗冠心病、动脉粥样硬化、贫血、脑软化、肝病和癌症等的辅助药物。而绿色植物则是人类和动物VE的基本来源。近年来随着植物基因组学的发展和营养基因组学概念的提出, 通过快速分离植物营养代谢(VE)相关酶的基因, 最终解析和调控植物微量营养素代谢途径, 利用代谢工程的方法大大提高植物营养价值之策略正在逐步完善。本文对有关植物中VE生物合成途径和相关酶基因克隆研究现状, 以及VE在植物体 内的作用和功能研究进展进行了综述, 以期为VE作用机理的探寻和功能开发提供新思路。     

维生素E的功能、吸收与代谢(1)

维生素E（VE）是生育酚（tocopherols）和生育三烯酚（tocotrienols）的总称,是人和动物生殖、生长过程中的必需微量营养物质,具有抗氧化、抗衰老、抗癌和抗热应激反应的作用,能增强动物体的免疫力,改善肌肉品质,还与某些基因相互作用影响转录和表达等。α-生育酚主要是在十二指肠通过淋巴吸收的,而且约99％是以乳糜微粒的形式吸收的。VE的代谢是其侧链在细胞色素P-450的启动下．先经ω-羟基化再β-氧化降解生成CEHC。CYP3A是ω-氧化酶,CYP3A催化的VEω-氧化是VE代谢的限速步骤。现代的研究拟从分子水平来理解和描述VE的代谢和作用机制。     

三烯生育酚研究进展

三烯生育酚和生育酚统称为维生素E,是重要的脂溶性维生素。维生素E只能在植物或者光合细菌中合成,是人类和动物必需且只能通过食物等摄取的重要维生素。一直以来,由于三烯生育酚与生育酚相比,生物活性较低且分布范围较小,人们对其研究相对较少。近些年的研究发现,由于三烯生育酚和生育酚的结构相似,因此三烯生育酚具有与生育酚相同的抗氧化等功能;但又由于三烯生育酚含有不饱和的植基侧链,使得三烯生育酚还具有一些不同于生育酚的功能,比如保护神经免受损伤、降低胆固醇、保护脑细胞免受损伤等。因此,三烯生育酚逐渐成为了研究热点。根据维生素E的生物合成途径,人们也开始了对三烯生育酚的生物强化研究,其合成途径中第一个关键酶基因HGGT的过表达是目前三烯生育酚含量提高的最有效途径;将来还需结合其合成调控的分子机制及其吸收利用问题,开发针对三烯生育酚的功能型产品。从三烯生育酚的合成途径、生物学功能、生物强化等方面进行了综述,并对今后的研究重点提出了展望。     

三烯生育酚生物学功能及合成调控研究进展

介绍了三烯生育酚的生物合成途径,重点综述了三烯生育酚在神经保护、抗癌、降低胆固醇以及抗氧化等方面的优越生物学功能,以及利用关键酶的高效表达和前体物质水平的提高等植物代谢工程手段提高植物体内三烯生育酚生物合成水平的研究进展。     

天然维生素E的研究进展

维生素E是一类脂溶性、具抗氧化功能的维生素,按其来源可分为天然维生素E和人工合成维生素E.对天然维生素E的功能、生物合成途径以及相关酶基因的研究方面进行了综述.其中,维生素E合成相关酶基因已经克隆及定位,尤其VTE5的发现,为生育酚合成研究开辟了一条新途径.人们已经开始利用基因工程技术研究提高植物天然维生素E产量的方法.     

利用基因工程提高植物维生素E营养品质的策略

维生素E是一种对植物、动物和人类都具有重要作用的脂溶性维生素。而植物则是人类维生素E的主要来源。对维生素E的结构和合成途径进行了简单的介绍,并重点综述了利用基因工程提高植物维生素E营养品质的策略。这些策略主要包括导入编码影响维生素E总量相关酶的基因来提高维生素E的总量;导入编码影响维生素E组成相关酶的基因,提高α-生育酚在总生育酚中所占的比例,从而提高维生素E的活性。     

γ-生育三烯酚联合亚砷酸对急性早幼粒细胞NB4生长的抑制作用及机制

目的:研究γ-生育三烯酚联合亚砷酸对急性早幼粒细胞NB4生长的抑制作用及可能的分子机制。方法:采用CCK-8、细胞周期实验检测细胞增殖、利用激光共聚焦显微镜、Annexin V/PI染色、Caspase活性检测、Western Blot等方法测定细胞凋亡。采用1μmol/L ATO及不同浓度(0、15、30、45μmol/L)的γ-生育三烯酚处理NB4细胞24、48和72小时,通过CCK-8检测细胞的增殖情况,流式细胞术、激光共聚焦显微镜检测细胞周期和凋亡情况,检测Caspase3,8,9的活性,Western Blot检测细胞中c-caspase-3、Bcl-2和survivin的蛋白表达。结果:γ-生育三烯酚联合亚砷酸显著抑制NB4细胞增殖(P0.01),且随着作用时间延长和γ-生育三烯酚浓度的增加,其增殖抑制作用增强;细胞周期阻滞在S期,S期的比例由38.21%±2.99上升到50.31%±5.03;γ-生育三烯酚联合亚砷酸诱导NB4细胞凋亡,1μmol/L ATO联合15、30μmol/L的γ-生育三烯酚处理48h后,细胞活率分别为82.27%±3.16、66.97%±3.17、12.63%±2.66;1μmol/L ATO联合30μmol/L的γ-生育三烯酚处理后,NB4细胞caspase-3,-8,-9的活性均较ATO单独用药组显著增高,c-caspase-3表达增高而Bcl-2和survivin蛋白的表达无明显变化。结论:生育三烯酚联合亚砷酸对急性早幼粒细胞NB4的生长具有抑制作用,此作用可能与抑制增殖并诱导凋亡相关,其作用靶点可能与促进Cas-pase诱导的凋亡有关。     

植物维生素E基因工程研究进展

维生素E(vitamin E)是一种脂溶性维生素,是生物体内最主要的抗氧化剂之一。本文综述了植物维生素E的合成途径及所涉及的相关基因,针对提高植物中维生素E含量的基因工程改造,提出三条途径,即提高代谢底物水平、提高植物生育酚总量和提高α 生育酚比例,分析了维生素E基因工程改造过程中需要考虑的因素,最后展望了未来作物维生素E的品质改良的研究方向。     

植物维生素E生物强化研究进展

维生素E是一种只能在光合组织中合成的脂溶性小分子有机化合物,是人体和动物营养不可缺少的重要维生素。由于植物中维生素E含量较低,人类大多处于慢性缺乏维生素E--“隐性饥饿”的状态,而动物饲料中则需要添加外源合成的维生素E以满足其营养需求。因此,提高植物中维生素E的含量是改善维生素E缺乏的重要途径之一。从维生素E的合成途径入手,详细地综述了维生素E合成关键酶基因的表达变化以及前体物质的含量变化对维生素E合成的影响,发现三烯生育酚和α-生育酚的生物强化效果较好,而生育酚总量提高受限;进而从遗传的角度探讨了维生素E合成受限的原因以及遗传上可能影响维生素E合成的其他代谢途径;最后结合可能影响维生素E合成的调控因子以及其前体物质的转运等方面为今后维生素E的生物强化提出了新的思路。     

From Arabidopsis to agriculture: engineering improved Vitamin E content in soybean

For more than 80 years, tocopherols have been known to be an essential nutrient, vitamin E, for humans and animals. Work in recent years has concentrated on dissecting tocopherol biosynthesis to engineer the pathway in agricultural crops. Molecular dissection of the pathway in plants is now complete with the cloning and characterization of the gene for Arabidopsis MPBQ/MSBQ methyltransferase (VITAMIN E 3; VTE3). Alison Van Eennemaan and colleagues used seed-specific expression of two vitamin E pathway methyltransferases to engineer increased vitamin E activity in soybeans.     

Progress in the dissection and manipulation of vitamin E synthesis

Tocochromanols are a group of four tocopherols and four tocotrienols that collectively constitute vitamin E, an essential nutrient in the human diet. Tocochromanols are only synthesized in oxygenic photosynthetic organisms. Although they have similar antioxidant activities in vitro, the individual tocochromanols vary widely in their in vivo vitamin E activities. During the past several years, mutant and transgenic approaches in model organisms, particularly in Arabidopsis thaliana and Synechocystis sp. PCC6803, have allowed the full complement of core pathway genes to be isolated and studied. Pathway engineering with these genes has provided significant insights into the molecular genetic and biochemical control of tocochromanol biosynthesis in plants. The resulting knowledge base is driving efforts to manipulate the levels of this essential nutrient in staple crops for populations in the developed and developing world.     

Acetoacetyl-CoA thiolase regulates the mevalonate pathway during abiotic stress adaptation

Acetoacetyl-CoA thiolase (EC 2.3.1.9), also called thiolase II, condenses two molecules of acetyl-CoA to give acetoacetyl-CoA. This is the first enzymatic step in the biosynthesis of isoprenoids via mevalonate (MVA). In this work, thiolase II from alfalfa (MsAACT1) was identified and cloned. The enzymatic activity was experimentally demonstrated in planta and in heterologous systems. The condensation reaction by MsAACT1 was proved to be inhibited by CoA suggesting a negative feedback regulation of isoprenoid production. Real-time RT-PCR analysis indicated that MsAACT1 expression is highly increased in roots and leaves under cold and salinity stress. Treatment with mevastatin, a specific inhibitor of the MVA pathway, resulted in a decrease in squalene production, antioxidant activity, and the survival of stressed plants. As expected, the presence of mevastatin did not change chlorophyll and carotenoid levels, isoprenoids synthesized via the plastidial MVA-independent pathway. The addition of vitamin C suppressed the sensitive phenotype of plants challenged with mevastatin, suggesting a critical function of the MVA pathway in abiotic stress-inducible antioxidant defence. MsAACT1 over-expressing transgenic plants showed salinity tolerance comparable with empty vector transformed plants and enhanced production of squalene without altering the 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) activity in salt-stress conditions. Thus, acetoacetyl-CoA thiolase is a regulatory enzyme in isoprenoid biosynthesis involved in abiotic stress adaptation.     

Intraerythrocytic stages of Plasmodium falciparum biosynthesize vitamin E

The 2-C-methyl-d-erythritol-4-phosphate and shikimate pathways were found to be active in Plasmodium falciparum and both can result in vitamin E biosynthesis in plants and algae. This study biochemically confirmed vitamin E biosynthesis in the malaria parasite, which can be inhibited by usnic acid. Furthermore, we found evidence pointing to a role of this vitamin in infected erythrocytes. These findings not only contribute to current understanding of P. falciparum biology but also reveal a pathway that could serve as a chemotherapeutic target.     

Biosynthesis,regulation and functions of tocochromanols in plants

Tocopherols and tocotrienols have been originally identified as essential nutrients in mammals based on their vitamin E activity. These lipid-soluble compounds are potent antioxidants that protect polyunsaturated fatty acids from lipid peroxidation. The biosynthesis of tocopherols and tocotrienols occurs exclusively in photosynthetic organisms. The biosynthetic precursors and the different pathway intermediates have been identified by biochemical studies and the different vitamin E biosynthetic genes (VTE genes) have been isolated in several plants and cyanobacteria. The characterization of transgenic plants overexpressing one or multiple VTE genes combined with the study of vitamin E deficient mutants allows from now on understanding the regulation and the function of tocopherols and tocotrienols in plants.     

Vitamin B1 de novo synthesis in the human malaria parasite Plasmodium falciparum depends on external provision of 4-amino-5-hydroxymethyl-2-methylpyrimidine

Vitamin B1 (thiamine) is an essential cofactor for several key enzymes of carbohydrate metabolism. Mammals have to salvage this crucial nutrient from their diet to complement their deficiency of de novo synthesis. In contrast, bacteria, fungi, plants and, as reported here, Plasmodium falciparum, possess a vitamin B1 biosynthesis pathway. The plasmodial pathway identified consists of the three vitamin B1 biosynthetic enzymes 5-(2-hydroxy-ethyl)-4-methylthiazole (THZ) kinase (ThiM), 4-amino-5-hydroxymethyl-2-methylpyrimidine (HMP)/HMP-P kinase (ThiD) and thiamine phosphate synthase (ThiE). Recombinant PfThiM and PfThiD proteins were biochemically characterised, revealing K(m)app values of 68 microM for THZ and 12 microM for HMP. Furthermore, the ability of PfThiE for generating vitamin B1 was analysed by a complementation assay with thiE-negative E. coli mutants. All three enzymes are expressed throughout the developmental blood stages, as shown by Northern blotting, which indicates the presence of the vitamin B1 biosynthesis enzymes. However, cultivation of the parasite in minimal medium showed a dependency on the provision of HMP or thiamine. These results demonstrate that the human malaria parasite P. falciparum possesses active vitamin B1 biosynthesis, which depends on external provision of thiamine precursors.