亚硒酸钠诱导的晶状体蛋白质聚合作用

不仅在体内,而且在体外亚硒酸钠可引起晶状体蛋白质聚合。将亚硒酸钠加到pH7.4的晶状体蛋白质溶液中,在37℃保温30min后观察到蛋白质溶液变混浊,随时间的延长混浊程度加重并有沉淀形成。经SDS聚丙烯酰胺凝胶电泳发现,加硒保温后形成的不溶性蛋白质中有大量的高分子聚合物。当加入二硫苏糖醇后混浊的蛋白质溶液变清,其中的高分子聚合物也基本消失,我们还发现;在亚硒酸钠使晶状体蛋白质变混浊的同时,蛋白质巯基减少,而蛋白质结合的硒量增加,且二者之间有较固定的比例关系,即蛋白质上每增加一个硒原子,蛋白质巯基就减少4.26个。当用二硫苏糖醇还原后,68％的硒从蛋白质中释放出来。这些结果表明,亚硒酸钠可引起大鼠晶状体水溶性蛋白质聚合,其可能方式如下:4PSH+SeO_3~-→PSSP+PS-Se-SP+H_2O+2OH~-这可能是亚硒酸钠诱发白内障的主要原因。     

Variation of the level of mercury and metallothionein in the kidneys and liver of rats with time of exposure to sodium selenite

Sodium selenite was administered to rats before, after, and simultaneously with mercuric chloride. In all animal groups, mercury was administered intravenously in doses of 0.5 mg/kg every other day for two weeks. Selenium was given intragastrically either in a single dose of 7.0 mg Se/kg or in repeated doses of 0.1 mg Se/kg every day for weeks. It was demonstrated that, depending on the administration schedule, selenium induced significant changes in the binding of mercury by soluble fraction proteins both in the kidneys and in the liver. In every exposure, the mercury content decreased mainly in the low-molecular weight proteins, and the level of metallothionein-like proteins was diminished in the both organs. In the kidneys, the mercury content showed a correlation with the level of metallothionein (r=0.78). Amounts of mercury below 10 μg/g kidney do not stimulate metallothionein biosynthesis in this organ. A distinct interaction effect was observed in the case of a simultaneous administration of equimolar amounts of both the metals in question.     

Chemical forms of selenium present in rat and ram spermatozoa

In vivo and in vitro studies were conducted to investigate the chemical forms by ion-exchange chromatography of selenium (Se) present in rat and ovine spermatozoa. After injection with ⁷⁵Se-selenite, the form of ⁷⁵Se in rat sperm was selenocysteine, but selenocysteine and selenomethionine (SeMet) were present in ovine sperm. Presumably, synthesis of SeMet by rumen microbes are responsible for its presence in ovine sperm. In vitro incubation of ram sperm with selenocysteine or SeMet produced no changes, but incubation with selenite produced a compound that eluted one fraction before SeMet from the ion-exchange column. After treatment of this fraction with mercaptoethanol, it eluted in a later fraction upon rechromatography, suggesting it to be selenodicysteine. This compound is apparently formed because of high levels of cysteine in semen. Cysteine, reduced glutathione, and oxidized glutathione were also found in semen. The significance of the results is discussed.     

SELENIUM: AN ESSENTIAL ELEMENT FOR GROWTH OF THE COASTAL MARINE DIATOM THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE)1,2

An obligate requirement for selenium is demonstrated in axenic culture of the coastal marine diatom Thalassiosira pseudonana (clone 3H) (Hust.) Hasle and Heimdal grown in artificial seawater medium. Selenium deficiency was characterized by a reduction in growth rate and eventually by a cessation of cell division. The addition of 10⁻¹⁰ M Na₂SeO₃ to nutrient enriched artificial seawater resulted in excellent growth of T. pseudonana and only a slight inhibition of growth occurred at Na₂SeO₃ concentrations of 10⁻³ and 10⁻² M. By contrast, Na₂SeO₄ failed to support growth of T. pseudonana when supplied at concentrations less than 10⁻⁷ M and the growth rate at this concentration was only one quarter of the maximum growth rate. The addition of 10⁻³ and 10⁻² M Na₂SeO₄ to the culture medium was toxic and cell growth was completely inhibited. Eleven trace elements were tested for their ability to replace the selenium requirement by this alga find all were without effect. In selenium-deficient and selenium-starved cultures of T. pseudonana cell volume increased as much as 10-fold as a result of an increase in cell length (along the pervalvar axis) but cell width was constant. It is concluded that selenium is an indispensable element for the growth of T. pseudonana and it should be included as a nutrient enrichment to artificial seawater medium when culturing this alga.     

亚硒酸钠对肝细胞L-02端粒酶活性和端粒长度的作用

通过研究硒对端粒酶活性和端粒长度的作用 ,探讨硒抗衰老的生物学机制。实验以人肝细胞株L 0 2为研究对象 ,分别补充 0 .5和 2 .5 μmol L亚硒酸钠 ,采用端粒重复序列扩增 焦磷酸根酶联发光法、逆转录聚合酶链式反应法及流式荧光原位杂交法 ,分别检测细胞的端粒酶活性、人端粒酶逆转录酶催化亚基基因 (hTERT)的表达及端粒长度的变化。结果表明 :常规培养的肝细胞株L 0 2的端粒酶活性和hTERT基因表达水平均较低。补充 0 .5和2 .5 μmol L亚硒酸钠三周后细胞生长状况良好、端粒酶活性和hTERT基因表达水平显著性增高 ,且呈一定的剂量 效应关系。细胞补充亚硒酸钠四周后端粒长度显著增长。说明营养浓度的亚硒酸钠可通过提高端粒酶活性和增长端粒长度来减缓L 0 2肝细胞衰老、延长细胞寿命。     

Rad52 has a role in the repair of sodium selenite-induced DNA damage in Saccharomyces cerevisiae

Selenium (Se) is a chemo-preventive agent that has been shown to have a protective role against cancer. The inorganic form of Se, sodium selenite (Na₂SeO₃), has frequently been included in various chemo-prevention studies, and this commercially available form of Se is used as dietary supplement by the public. Because high doses of this Se compound can be toxic, the underlying molecular mechanisms of sodium selenite toxicity need to be elucidated. Recently, we have reported that sodium selenite is acting as an oxidizing agent in the budding yeast Saccharomyces cerevisiae, producing oxidative damage to DNA. This pro-oxidative activity of sodium selenite likely accounted for the observed DNA double-strand breaks (DSB) and yeast cell death. In this study we determine the genetic factors that are responsible for repair of sodium selenite-induced DSB. We report that the Rad52 protein is indispensable for repairing sodium selenite-induced DSB, suggesting a fundamental role of homologous recombination (HR) in this repair process. These results provide the first evidence that HR may have a fundamental role in the repair of sodium selenite-induced toxic DNA lesions.     

Glutathione contributes to the efflux of selenium from hepatoma cells

Selenite is a selenium source for selenoprotein biosynthesis in mammalian cells. Although previous studies have suggested the involvement of glutathione (GSH) and/or thioredoxin reductase in selenite metabolism, intracellular selenite metabolism remains largely unknown. Here, we report that GSH depletion did not affect the amount of selenoprotein in Hepa 1–6 cells, suggesting that GSH does not play a central role in the reduction of selenite in selenoprotein biosynthesis. On the other hand, we found that GSH is involved in the efflux of low-molecular-weight selenium compounds from cells, presumably via the formation of selenodiglutathione. Moreover, selenite inhibited the efflux of a fluorescent bimane-GS conjugate that is mediated by ATP-dependent multidrug-resistant proteins, implying the existence of an active transporter for selenodiglutathione. This is the first report demonstrating that GSH plays a role in selenium excretion from cells by forming a GSH-conjugate, which may contribute to the distribution, detoxification, and homeostasis of selenium in the body.     

亚硒酸钠对西门塔尔母牛发情周期生殖激素分泌的影响

选用12头18月龄,体况良好,体重380 kg的西门塔尔牛育成母牛,采用完全随机区组设计分为4组,研究亚硒酸钠(0、0.3、0.6和0.9 mg Se/kg DM)对发情周期外周血清促黄体素、促卵泡素、孕酮和雌二醇分泌的影响。结果表明:日粮添加亚硒酸钠后发情周期促黄体素、促卵泡素、孕酮和雌二醇分泌水平提高,0.3 mg/kg组和0.6 mg/kg组显著高于对照组(P<0.05),0.3 mg/kg组较0.6 mg/kg组高(P>0.05)。根据试验结果推断以亚硒酸钠为硒源,添加0.3 mg Se/kg DM对发情周期生殖激素分泌有显著促进作用,兼顾基础日粮的含硒量,建议日粮硒水平为0.37 mg Se/kg DM。     

Mitochondrial outer-membrane E3 ligase MUL1 ubiquitinates ULK1 and regulates selenite-induced mitophagy

Mitochondria serve as membrane sources and signaling platforms for regulating autophagy. Accumulating evidence has also shown that damaged mitochondria are removed through both selective mitophagy and general autophagy in response to mitochondrial and oxidative stresses. Protein ubiquitination through mitochondrial E3 ligases plays an integrative role in mitochondrial outer membrane protein degradation, mitochondrial dynamics, and mitophagy. Here we showed that MUL1, a mitochondria-localized E3 ligase, regulates selenite-induced mitophagy in an ATG5 and ULK1-dependent manner. ULK1 partially translocated to mitochondria after selenite treatment and interacted with MUL1. We also demonstrated that ULK1 is a novel substrate of MUL1. These results suggest the association of mitochondria with autophagy regulation and provide a new mechanism for the beneficial effects of selenium as a chemopreventive agent.     

NRT1.1B improves selenium concentrations in rice grains by facilitating selenomethinone translocation

Selenium (Se) is an essential trace element for humans and other animals, yet approximately one billion people worldwide suffer from Se deficiency. Rice is a staple food for over half of the world's population that is a major dietary source of Se. In paddy soils, rice roots mainly take up selenite. Se speciation analysis indicated that most of the selenite absorbed by rice is predominantly transformed into selenomethinone (SeMet) and retained in roots. However, the mechanism by which SeMet is transported in plants remains largely unknown. In this study, SeMet uptake was found to be an energy‐dependent symport process involving H⁺ transport, with neutral amino acids strongly inhibiting SeMet uptake. We further revealed that NRT1.1B, a member of rice peptide transporter (PTR) family which plays an important role in nitrate uptake and transport in rice, displays SeMet transport activity in yeast and Xenopus oocyte. The uptake rate of SeMet in the roots and its accumulation rate in the shoots of nrt1.1b mutant were significantly repressed. Conversely, the overexpression of NRT1.1B in rice significantly promoted SeMet translocation from roots to shoots, resulting in increased Se concentrations in shoots and rice grains. With vascular‐specific expression of NRT1.1B, the grain Se concentration was 1.83‐fold higher than that of wild type. These results strongly demonstrate that NRT1.1B holds great potential for the improvement of Se concentrations in grains by facilitating SeMet translocation, and the findings provide novel insight into breeding of Se‐enriched rice varieties.