含硒生物大分子化合物研究进展

硒是人体必需的微量元素 ,对人类健康有着重要意义 .研究证明 :硒与多种疾病如心血管系统疾病、癌症、HIV感染等相关 ,硒是硒蛋白的组成成分 ,并且在硒酶的活性中心发现含有硒半胱氨酸 ,说明硒与某些含硒生物大分子的结构和硒酶活性有着密切联系 .对含硒的生物大分子 (硒蛋白、硒酶、含硒多糖、含硒核酸等 )已作了大量有意义的研究工作 ,认识它们的重要作用有助于进一步探明硒的生物学作用机理 ,并对含硒活性物质开发具有促进作用     

硒的生物功能

谷胱甘肽过氧化物酶、甲状腺素５′脱碘酶等多种含硒酶的作用机制已研究得较为详细．缺硒是克山病发病的直接因素．体内适当的硒含量具有抑癌功能．硒蛋白中硒参入到蛋白分子是通过硒半胱氨酸－ｔＲＮＡ 识别ｍ ＲＮＡ 中特导的ＵＧＡ 密码子将硒半胱氨酸插入到硒蛋白中的     

硒代半胱氨酸的生物合成及参入

硒代半胱氨酸是蛋白硒的主要存在形式，其合成和参入有不同于其它氨基酸的生物学特点系统．阐述了原核生物和真核生物的硒代半胱氨酸的合成途径和参入机制，并比较了原核生物和真核生物硒蛋白基因中硒代半胱氨酸插入序列元件的结构特点．     

硒及富硒食品研究进展

硒是人体必需的微量元素,具有抗氧化、抗衰老、防癌抗癌作用和化学防癌潜力。国内外研究应用植物或微生物作为硒的生物载体,主要集中在茶叶、水稻、食用菌、酵母和大蒜等食品上。植物性食品中生物可利用的硒是以甲基硒代半胱氨酸的形式存在。     

植物体内含硒生物大分子基础与应用研究进展

植物硒主要以硒蛋白、硒多糖、硒核酸及硒酶等生物大分子形式存在，它们大多是低毒的生物活性物质．了解植物硒的分布规律、生理生化作用、测定方法等基础性研究和含硒生物大分子的研究进展，对于进一步开发利用植物中的硒具有重要意义。     

高效液相色谱-氢化物发生原子荧光光谱法测定食品中多形态硒含量

研究基于高效液相色谱-氢化物发生原子荧光光谱建立了一种适用于富硒蛋白粉、富硒大米、富硒香菇和富硒酵母等富硒食品中硒酸根、硒代胱氨酸、甲基硒代半胱氨酸、硒代蛋氨酸的检测方法。样品经Tris缓冲液提取,蛋白酶和胰蛋白酶酶解,以V(20mmol/L磷酸氢二胺水溶液,pH=6.0)∶V(甲醇)=98∶2为流动相,经Hamilton PRP-X100阴离子交换色谱柱分离测定。结果表明,4种硒形态化合物在5~100μg/kg范围内线性良好(R²＞0.999),方法检出限可达25~50μg/kg,平均加标回收率为81.37%~93.80%,且RSD为2.80%~7.22%。应用此方法对4种市售富硒食品(富硒蛋白粉、富硒大米、富硒香菇和富硒酵母)中4种硒形态化合物进行检测,前处理步骤简单,测定快速、准确度和灵敏度高,为食品中硒形态评价和质量控制提供了方法和依据。     

恩施续断中含硒化合物体外抗氧化活性分析

以恩施续断为原料,用蒸馏水、0.5 mol/L Na Cl、75%乙醇、0.1 mol/L Nao H四种溶剂对续断中不同种类硒蛋白进行提取.用热水浸提法提取硒多糖,用原子荧光法测定不同提取物中硒元素的含量,分析了续断中硒的赋存形态.并采用邻苯三酚自氧化法测定续断不同提取物清除超氧阴离子(O2-·)的能力,用Fenton法测定其清除羟自由基(·OH)的能力,探究了含硒化合物的抗氧化活性.结果表明:续断中硒的总含量为1.538μg/g,蛋白质、多糖中都赋存一定量的硒;蛋白硒是续断中硒的主要赋存形态.四种溶剂提取物中碱溶性硒蛋白的含量最高,它的含量可达总可溶性蛋白的57.28%.按照相同质量样品中结合硒量的多少,可以得出含硒量:总蛋白硒多糖硒;醇溶性硒蛋白盐溶性硒蛋白碱溶性硒蛋白水溶性硒蛋白.恩施续断中各种含硒化合物都有一定的清除超氧阴离子和羟自由基的能力,且不同溶剂提取物的清除率都不同.其中醇溶性提取物清除超氧自由基的能力最好,碱溶性提取物清除超氧自由基的能力最弱;硒多糖清除羟自由基的能力最强.     

植物硒的研究进展

微量元素硒不仅是人和动物的必要的营养元素，也是植物生长发育的不可缺乏的元素，植物体内的硒主要以硒蛋白、硒核酸，硒多糖等多种生物大分子以及硒代半胱氨酸和硒代蛋氨酸等生物小人子有机合物存在，在全综述了植物在自然界硒生态链转化中的地位和作用，植物对硒的吸收方式及代谢途径，硒在植物中的生物学效应，植物硒开发利用现状及方向从多方面分析讨论了植物硒的研究进展。     

不同硒水平地区蛋白及其亚基间硒的分布差异

利用ＳＤＳ－ＰＡＧＥ和ＨＰＬＣ－荧光检测法对大豆含硒蛋白或多肽进行分离和硒含量测定，在“〉２ＳＤ”为含硒条带的约定下，从所采集恩施，北京，启东样品中分别检出了１９，１２和１０条含硒蛋白或亚基条带，并初步估算了它们的分子量和含硒量，根据这些蛋白条带的归属分析，发现３个地区样品大豆乳清蛋白结合硒的量最多，１１Ｓ组分结合硒的量次之，７Ｓ组分结合硒的量最少，经过对不同硒含量样品进行比较后认为，大豆乳清蛋白     

大豆硒蛋白药理作用研究

开展了大豆硒蛋白的动物药、毒理实验 ,结果表明 ,大豆硒蛋白能明显增强小鼠抗疲劳能力 ,并能显著增加小鼠免疫器官 (脾脏和胸腺 )的重量。大豆硒蛋白对体外生长的 SP2 /0小鼠骨髓瘤细胞以及对小鼠体内 SP2 /0实体瘤的生长具有明显的抑制和杀伤作用。连续接受高剂量大豆硒蛋白的小鼠在一个月的观察期内无一死亡 ,且均未见到任何异常反应 ,证实了大豆硒蛋白的安全性。     

Identification of a novel translation factor necessary for the incorporation of selenocysteine into protein

During the biosynthesis of selenoproteins in both prokaryotes and eukaryotes, selenocysteine is cotranslationally incorporated into the nascent polypeptide chain through a process directed by a UGA codon that normally functions as a stop codon. Recently, four genes have been identified whose products are required for selenocysteine incorporation in Escherichia coli. One of these genes, selC, codes for a novel transfer RNA species (tRNAUCA) that accepts serine and cotranslationally inserts selenocysteine by recognizing the specific UGA codon. The serine residue attached to this tRNA is converted to selenocysteine in a reaction dependent on functional selA and selD gene products. By contrast, the selB gene product (SELB) is not required until after selenocysteyl-tRNA biosynthesis. Here we present evidence indicating that SELB is a novel translation factor. The deduced amino-acid sequence of SELB exhibits extensive homology with the sequences of the translation initiation factor-2 (IF-2) and elongation factor Tu (EF-Tu). Furthermore, purified SELB protein binds guanine nucleotides in a 1:1 molar ratio and specifically complexes selenocysteyl-tRNAUCA, but does not interact with seryl-tRNAUCA. Thus, SELB could be an amino acid-specific elongation factor, replacing EF-Tu in a special translational step.     

Biosynthesis of selenosubtilisin: A novel way to target selenium into the active site of subtilisin

Glutathione peroxidase （GPx, EC1.11.1.9）, an important anti-oxidative selenoenzyme, can catalyze the reduction of harmful hydroperoxides with concomitant glutathione, thereby protecting cells and other biological issues against oxidative damage. It captures considerable interest in redesign of its function for either the mechanism study or the pharmacological development as an antioxidant. In order to develop a general strategy for specifically targeting and operating selenium in active sites of enzymes, the catalytically essential residue selenocysteine （Sec） was first successfully bioincorporated into the catalytic center of subtilisin by using an auxotrophic expression system. The studies of the catalytic activity and the steady-state kinetics demonstrated that selenosubtilisin is an excellent GPx-like biocatalyst. In comparison with the chemically modified method, biosynthesis exhibits obvious advantages： Sec could be site-directly incorporated into active sites of enzymes to overcome the non-specificity generated by chemical modification. This study provides an important strategy for specifically targeting and operating selenium in the active site of an enzyme.     

Type I iodothyronine deiodinase is a selenocysteine-containing enzyme.

Although thyroxine (3,5,3',5'-tetraiodothyronine, T4) is the principal secretory product of the vertebrate thyroid, its essential metabolic and developmental effects are all mediated by 3,5,3'-triiodothyronine (T3), which is produced from the prohormone by 5'-deiodination. The type-I iodothyronine deiodinase, a thiol-requiring propylthiouracil-sensitive oxidoreductase, is found mainly in liver and kidney and provides most of the circulating T3(1) but so far this enzyme has not been purified. Using expression cloning in the Xenopus oocyte, we have isolated a 2.1-kilobase complementary DNA for this deiodinase from a rat liver cDNA library. The kinetic properties of the protein expressed in transient assay systems, the tissue distribution of the messenger RNA, and its changes with thyroid status, all confirm its identity. We find that the mRNA for this enzyme contains a UGA codon for selenocysteine which is necessary for maximal enzyme activity. This explains why conversion of T4 to T3 is impaired in experimental selenium deficiency and identifies an essential role for this trace element in thyroid hormone action.     

In silico identification of silkworm selenoproteomes

Selenium (Se) is an essential trace element in vivo. Its biological function is mainly exerted through selenoproteins. Selenocysteine (Sec), the active site of selenoproteins, is incorporated into the protein at an in-frame TGA codon under the guidance of Sec insertion sequence (SECIS) element in the 3′-untranslated region (UTR) of the gene. In this work, a method was developed and a series of programs were edited by PERL language to in silico identify selenoproteomes from the genome of domesticated silkworm (Bombyx mori). Out of 18510 annotated genes, 6348 was terminated with TGA codons, 249 containing both in-frame TGAs and SECIS elements in the 3′-UTRs. Alignments of those selenoprotein candidates with their cysteine (Cys)-containing homologs revealed that 52 genes had TGA/Cys pairs and similar flanking regions around the in-frame TGAs. Restricted by the patterns of SECIS elements only 5 genes were screened out to fully meet the requirements for selenoproteins. Among them glutathione S-transferase (GST) has been reported as a microbial selenoprotein, the other four are novel selenoproteins annotated as CG6024, CG5195, ATP-binding cassette transporter subfamily A (ABCA), and nuclear VCP-like protein. Derived from the general properties of GST, ABCA and VCP, silkworm selenoproteins may play important roles in redox regulation, Se storage and transportation, as well as cell apoptosis.     

Identification of selenocysteine insertion sequence (SECIS) element in eukaryotic selenoproteins by RNA Draw program

The computer program RNA Draw was used to identify the secondary structures in the 3′ untranslated regions (3′UTRs) of the mRNAs from 46 eukaryotic selenoproteins among 7 species. The program found one or two possible SECIS elements in these selenoproteins. The SECIS element consists of a stem-loop or hairpin structure with three conserved sequences of AUGA-(A)AA-GA. SECIS element was not found by the RNA Draw program in randomly selected non-selenoproteins. The results showed that SECIS element is the unique character of the genes of eukaryotic selenoproteins. Thus it is possible to use RNA Draw to search the SECIS elements in gene bank for potential new selenoproteins.     

Bioinformatic prediction of selenoprotein genes in the dolphin genome

Selenium (Se), an essential trace element in vivo, is present mainly as selenocystein (Sec) in various selenoproteins. The Sec residue is translated from an in-frame TGA codon, which traditionally functions as a stop codon. Prediction of selenoprotein genes is difficult due to the lack of an effective method for distinguishing the dual function of the TGA codon in the open reading frame of a selenoprotein gene. In this article a eukaryotic bioinformatic prediction system that we have developed was used to predict selenoprotein genes from the genome of the common bottlenose dolphin, Tursiops truncatus. Sixteen selenoprotein genes were predicted, including selenoprotein P and glutathione peroxidase. In particular, a type II iodothyronine deiodinase was found to have two Sec residues, while the type I iodothyronine deiodinase gene has two alternative splice forms. These results provide important information for the investigation of the relationship between a variety of selenoproteins and the evolution of the marine-living dolphin.     

猕猴桃微量硒的测定和施加硒肥的比较研究

用DAN荧光法测定了施硒肥和未施硒肥的猕猴桃花、叶、果中硒含量,结果表明：在相同的土壤营养等条件下,施加硒肥的猕猴桃中牺含量明显比未施硒肥的猕猴桃中硒含量高,且硒在猕猴桃植株中各部位的分布为：叶＞花＞果,提示场肥叶面喷施将比上施效果显著。