Selenium and Glutathione Peroxidase Levels in Lambs Receiving Feed Supplemented with Sodium Selenite or Selenomethionine

Twenty-one 6 months old female lambs were divided into 7 groups and fed a basal diet containing 0.13 mg Se/kg. The basal diet was further supplemented with 0, 0.1, 0.5 or 1.0 mg Se/kg either as sodium selenite or as selenomethionine, and was fed for 10 weeks. Both feed additives produced an increase in the selenium concentration in the tissues analysed. Significant correlations were found between the concentrations of selenomethionine or sodium selenite added to the feed and the subsequent tissue levels. However, the selenium levels seemed to plateau at approximately 0.5 mg Se/kg of supplemented sodium selenite. The total glutathione peroxidase (GSH-Px) activity of the tissues increased when the selenium supplementation increased from 0 to 0.1 mg/kg for both selenium compounds. With further increase in selenium supplementation the GSH-Px activity in the tissues plateaued except in the blood where the activity continued to rise with increasing selenomethionine supplementation. The selenium dependent GSH-Px activity in the liver rose with increasing selenomethionine supplementation, but approached a plateau when 0.1 mg Se/kg as sodium selenite was added to the feed. The selenium concentration in whole blood responded more rapidly to the selenium supplementation than did GSH-Px activity. The experiment indicates that the optimal selenium concentration in the feed is considerably higher than 0.1 mg Se/kg, and that selenium levels of 1.0 mg/kg in the feed do not result in any risk for the animals or the consumers of the products.     

Influence of Dietary Sodium Selenite on Tissue Selenium Levels of Growing Pigs

Twenty Norwegian Landrace pigs were divided into 5 groups and fed a basal diet consisting of a mixture of dried skim milk and whey powder together with ground barley. The diet was supplemented with 0, 0.2, 0.8, 1.2 and 2.2 μg selenium as sodium selenite and was fed for 12 weeks. The muscle selenium level was increased by a factor of about 4 and the liver selenium by a factor of about 12 when the dietary selenium supplement was increased from zero to 2.2 μg/g. There was a significant linear correlation between dietary selenium and selenium concentrations in tissues. Possible benefit for humans consuming meat from animals having received the selenium doses used in this experiment are discussed. dietary selenium; tissue levels; pigs.     

Selenium Concentrations in Tissues and Eggs of Growing and Laying Chickens Fed Sodium Selenite at Different Levels

Growing and laying chickens were fed graded levels of selenium in the form of sodium selenite. One day old Norwegian bred broiler chickens and 20 weeks old Norwegian bred White Leghorn chickens were divided into 5 groups each and fed a basal diet supplemented with 0, 0.1, 1.0, 3.0 or 6.0 μg Se/g for 6 and 31 weeks, respectively. At the end of the experiments significantly higher concentrations of selenium were found in the groups fed 1.0, 3.0 and 6.0 μg Se/g diet compared to the control group. Correspondingly higher concentrations of selenium were found in egg samples. The increase in egg yolk selenium was much higher than in egg white. Significant correlations were found between the amounts of selenium added to the ration and the selenium concentrations in liver, kidney, breast muscle, egg white, yolk and homogenized egg. There were no differences in body weight gain and egg production between the groups. A possible positive contribution to animal and human health of selenium supplementation of animals’ diet above the required level is discussed.     

Sodium Selenite Prevents Paraquat-Induced Neurotoxicity in Zebrafish

Considering the antioxidant properties of sodium selenite (Na₂SeO₃) and the involvement of oxidative stress events in paraquat-induced neurotoxicity, this study investigated the protective effect of dietary Na₂SeO₃ on biochemical and behavioral parameters of zebrafish exposed to paraquat (PQ). Fish were pretreated with a Na₂SeO₃ diet for 21 days and then PQ (20 mg/kg) was administered intraperitoneally with six injections for 16 days. In the novel tank test, the Na₂SeO₃ diet prevented the locomotor impairments, as well as the increase in the time spent in the top area of the tank, and the exacerbation of freezing episodes. In the preference for conspecifics and in the mirror-induced aggression (MIA) tasks, Na₂SeO₃ prevented the increase in the latency to enter the area closer to conspecifics and the agonistic behavior of PQ-treated animals, respectively. Na₂SeO₃ prevented the increase of carbonylated protein (CP), reactive oxygen species (ROS), and nitrite/nitrate (NOx) levels, as well as the decrease in non-protein thiols (NPSH) levels. Regarding the antioxidant enzymatic defenses, Na₂SeO₃ prevented the increase in catalase (CAT) and glutathione peroxidase (GPx) activities caused by PQ. Altogether, dietary Na₂SeO₃ improves behavioral and biochemical function impaired by PQ treatment in zebrafish, by modulating not only redox parameters, but also anxiety- and aggressive-like phenotypes in zebrafish.     

亚硒酸钠对大鼠自身免疫性甲状腺炎影响的研究

目的:研究亚硒酸钠对大鼠自身免疫性甲状腺炎的影响。方法:Wistar大鼠分为对照组、自身免疫性甲状腺炎(EAT)组和硒治疗EAT组。诱发EAT大鼠模型,硒治疗EAT组灌胃给予亚硒酸钠。观察甲状腺激素谱、抗体和组织学改变。结果:硒治疗EAT组的TgAb、TmAb较EAT组明显下降。对照组、EAT组和硒治疗EAT组的FT3分别为(1．96±0．90)、(81．90±61．41)、(79．07±69．73)%,FT4分别为(3．01±1．21)、(41．94±20．35)、(17．72±3．22)%,TSH水平变化不大(P□0．05)。硒治疗EAT组与EAT组相比甲状腺淋巴细胞浸润减少,滤泡破坏减轻。结论:硒可使EAT大鼠自身抗体水平降低,病理改变减轻,并降低FT4的水平。     

Involvement of a Broccoli COQ5 Methyltransferase in the Production of Volatile Selenium Compounds

Selenium (Se) is an essential micronutrient for animals and humans but becomes toxic at high dosage. Biologically based Se volatilization, which converts Se into volatile compounds, provides an important means for cleanup of Se-polluted environments. To identify novel genes whose products are involved in Se volatilization from plants, a broccoli (Brassica oleracea var italica) cDNA encoding COQ5 methyltransferase (BoCOQ5-2) in the ubiquinone biosynthetic pathway was isolated. Its function was authenticated by complementing a yeast coq5 mutant and by detecting increased cellular ubiquinone levels in the BoCOQ5-2-transformed bacteria. BoCOQ5-2 was found to promote Se volatilization in both bacteria and transgenic Arabidopsis (Arabidopsis thaliana) plants. Bacteria expressing BoCOQ5-2 produced an over 160-fold increase in volatile Se compounds when they were exposed to selenate. Consequently, the BoCOQ5-2-transformed bacteria had dramatically enhanced tolerance to selenate and a reduced level of Se accumulation. Transgenic Arabidopsis expressing BoCOQ5-2 volatilized three times more Se than the vector-only control plants when treated with selenite and exhibited an increased tolerance to Se. In addition, the BoCOQ5-2 transgenic plants suppressed the generation of reactive oxygen species induced by selenite. BoCOQ5-2 represents, to our knowledge, the first plant enzyme that is not known to be directly involved in sulfur/Se metabolism yet was found to mediate Se volatilization. This discovery opens up new prospects regarding our understanding of the complete metabolism of Se and may lead to ways to modify Se-accumulator plants with increased efficiency for phytoremediation of Se-contaminated environments.Selenium (Se) has been studied extensively because of its essentiality for animals and humans and because of its toxicity at high dosage. Like a double-edged sword, Se is essential for the function of selenoenzymes but becomes toxic due to the nonspecific replacement of sulfur in sulfur-containing proteins (Stadtman, 1974; Brown and Shrift, 1982). The difference between beneficial and toxic levels of Se is quite narrow, making both Se deficiency and Se pollution common problems in different regions (Terry et al., 2000).Plants appear to be a promising solution for both sides of the Se problem (Pilon-Smits and LeDuc, 2009). Some crops have the ability to accumulate Se in health-beneficial chemical forms (Whanger, 2002; Dumont et al., 2006). Wheat (Triticum aestivum) grain grown in seleniferous soils accumulates selenomethionine (SeMet) and is one of the main dietary sources for Se (Lyons et al., 2005). Broccoli (Brassica oleracea var italica) has the ability to accumulate high level of Se-methylselenocysteine (SeMCys) and SeMet when grown on seleniferous soil (Cai et al., 1995). These selenoamino acids have been shown to be potent chemoprotective agents against cancer (Ip et al., 2000; Whanger, 2002). Other plant foods, such as garlic (Allium sativum) and Brazil nut (Bertholletia excelsa), have been enriched with Se and marketed as dietary Se supplements (Dumont et al., 2006). On the other hand, Se-hyperaccumulating plant species such as Astragalus bisulcatus and secondary accumulators such as Indian mustard (Brassica juncea) have attracted great interest for their ability to accumulate and volatilize Se for phytoremediation of Se-contaminated soils (Banuelos et al., 2007). Se volatilization converts highly toxic selenate and selenite into volatile dimethyl selenide (DMSe) and dimethyl diselenide (DMDSe), which are 500 to 700 times less toxic (Wilber, 1980). This process provides a low-cost, environmentally friendly, and highly efficient approach for cleanup of Se-contaminated environments (Banuelos et al., 2002; Pilon-Smits, 2005).The conversion of inorganic forms of Se into volatile Se in plants is believed to occur via the sulfur metabolic pathway, as outlined in Figure 1 (Terry et al., 2000; Sors et al., 2005). Se is present in soils predominantly as selenate (SeO₄²⁻) and selenite (SeO₃²⁻). While selenate is actively taken up into plants through sulfur transporters, selenite enters plant cells passively. The reduction of these oxidized forms of Se results in the production of selenoamino acids, such as selenocysteine (SeCys) and SeMet (Fig. 1). In Se-nonaccumulator plants, SeCys and SeMet are readily incorporated into proteins nonspecifically. In Se-accumulating plants, they are metabolized primarily into various nonproteinogenic selenoamino acids. These selenoamino acids can be further metabolized into the volatile Se compounds DMSe and DMDSe. While Se nonaccumulators mainly volatilize DMSe, accumulators primarily emit DMDSe (Terry et al., 2000; Ellis and Salt, 2003). Although Se volatilization is an important step in the Se cycle and provides a protective mechanism for plants and microorganisms to avoid toxicity in seleniferous environments, this metabolic process is not well understood.Open in a separate windowFigure 1.Outline of Se metabolism in plants. The open arrows indicate that both selenate (SeO₄²⁻) and selenite (SeO₃²⁻) in soil are taken up into plants. Se metabolism from selenate involves a series of reduction steps to form selenide (Se²⁻), which is assimilated into the selenoamino acids SeCys and SeMet. These selenoamino acids can be methylated and further metabolized into the volatile Se compounds DMDSe and DMSe. Abbreviations not defined in the text: SeMMet, Se-methylmethionine; SeMCysMT, Se-methylselenocysteine methyltransferase; SMetMT, S-adenosyl-l-Met:l-Met S-methyltransferase.Several sulfur metabolic pathway enzymes have been evaluated for their roles in stimulating Se volatilization (Pilon-Smits and LeDuc, 2009). Cystathionine-γ-synthase is believed to be involved in the formation of SeMet. Overexpression of this enzyme resulted in a 2- to 3-fold increased rate of Se volatilization in transgenic Indian mustard (Van Huysen et al., 2003). S-Adenosyl-l-Met:l-Met S-methyltransferase is responsible for the methylation of SeMet to Se-methylselenomethionine. Overexpression of this enzyme in Escherichia coli produced a 10-fold increase in the rate of Se volatilization when the bacteria were supplied with SeMet (Tagmount et al., 2002). Similarly, expression of a Se-methylselenocysteine methyltransferase to methylate SeCys to SeMCys was shown to stimulate a 2- to 3-fold increase of Se volatilization in transgenic Indian mustard (LeDuc et al., 2004). Although increasing the activities of these known sulfur metabolism enzymes causes increased Se volatilization, additional proteins may be involved in this process (Van Hoewyk et al., 2008).Microorganisms adapted to high-Se-contaminated environments develop mechanisms to convert inorganic Se compounds into volatile forms. Several methyltransferases from these bacteria were reported to stimulate the emission of DMSe and DMDSe by unknown mechanisms (Ranjard et al., 2002, 2004; Swearingen et al., 2006). To identify novel plant genes whose products promote the production of volatile Se and to gain a better understanding of the metabolic processes associated with Se volatilization, we used a genomics-based approach to isolate genes from broccoli, a plant species known to have high capacity to volatilize Se (Duckart and Waldron, 1992; Terry et al., 1992). Using this approach, a broccoli COQ5 methyltransferase gene designated BoCOQ5-2 was isolated. Functional complementation of a yeast coq5 mutant by BoCOQ5-2 confirmed its identity. BoCOQ5-2 was found to promote Se volatilization when it was expressed in both bacteria and transgenic Arabidopsis (Arabidopsis thaliana).COQ5 genes encode C-methyltransferases involved in the biosynthesis of ubiquinone or coenzyme Q (Dibrov et al., 1997; Lee et al., 1997). Ubiquinone is an important lipid-soluble compound found in membranes of almost all living species. Ubiquinone is well known for its function as the electron carrier in the mitochondrial respiratory chain for energy production. Moreover, it is widely accepted that ubiquinone also participates in other cellular processes, such as control of cellular redox status and detoxification of harmful reactive oxygen species (ROS; Kawamukai, 2002; Turunen et al., 2004). Indeed, plants with high ubiquinone levels have been demonstrated to be able to suppress ROS generation (Ohara et al., 2004). Increased ubiquinone biosynthesis was found to be associated with increases in tolerance to a variety of stresses in both plants and other organisms (Ohara et al., 2004; Zhang et al., 2007). Se has been shown to induce the production of ROS in Arabidopsis (Tamaoki et al., 2008). Ubiquinone functioning as an antioxidant may protect cells against the oxidative stress to facilitate Se metabolism.BoCOQ5 methyltransferase represents, to our knowledge, the first plant enzyme that is not known to be involved in sulfur/Se metabolism yet mediates Se volatilization. The cloning and characterization of the methyltransferase from the economically important vegetable crop broccoli extends our understanding of factors affecting Se metabolism. Such information may lead to ways to generate modified Se-accumulator plants with increased efficiency in the phytoremediation of Se-contaminated soils.     

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。     

Nanoparticles of Selenium as Species with Stronger Physiological Effects in Sheep in Comparison with Sodium Selenite

The present study was designed to compare the effects of nano red selenium and sodium selenite on the antioxidative activities of neutrophils and the hematological parameters in sheep. Fifteen sheep were randomly allocated into three groups. Groups 1 and 2 received selenium nanoparticles orally at 1 mg/kg and sodium selenite at 1 mg Se/kg for 10 consecutive days; group 3 served as the control. To assess the degrees of oxidative stress and of lipid peroxidation of the cellular membranes, the levels of thiobarbituric acid reactive substances (TBARS) were determined in serum samples that were collected at different supplementation intervals, i.e., after 0, 10, 20, and 30 days. In addition, hematological parameters in the serum samples were measured by routine procedures. It was found that TBARS levels in groups 1 and 2 were significantly higher on days 20 and 30 compared to the basal level on day 0. It was also found that on day 30, the TBARS activities in both treated groups were significantly higher than those of the controls (P < 0.05). These findings may explain the seemingly paradoxical effects of supplemental selenium on the indicators of oxidative stress, as the levels of TBARS were generally expected to decrease in the presence of selenium. There were no significant differences between the PCV and RBC values in the three groups. The white blood cell count (WBC) in group 1 showed a significant increase on days 20 and 30 in comparison with the control group. However, in group 2, there was a significant increase of the WBC value just on day 20 in comparison with the control group. Also, there were significant increases of the neutrophil counts and significant decreases of the lymphocyte counts on day 10 in group 1, in comparison with those in group 2 and controls, and on days 20 and 30 in groups 1 and 2 in comparison with those in the control group.     

BCAT4、CYP79F1和ESM1过表达提高西兰花细胞萝卜硫素含量

萝卜硫素(sulforaphane,SFN)是目前防癌抗癌效果最好的植物天然产物之一。十字花科芸薹属植物西兰花是生产SFN的重要材料。然而普通西兰花中SFN产量仍无法满足巨大的市场需求。之前单一基因改造提高植物SFN含量的策略效果并不理想。该研究从西兰花中克隆了SFN合成相关的支链氨基酸转移酶4编码基因BCAT4、细胞色素P450氧化酶编码基因CYP79F1和环硫修饰酶编码基因ESM1。分别以单基因导入和三基因串联导入的方式,通过农杆菌法转化西兰花愈伤组织,对所获得的转化细胞系中SFN的含量进行比较,以期获得SFN含量更高的细胞系,为通过细胞系大量培养获取SFN奠定基础。实验结果表明,目的基因BCAT4、CYP79F1、ESM1和B-C-E(BCAT4NSCYP79F1N-SESM1)都成功整合于宿主细胞基因组。BCAT4和B-C-E基因过表达细胞系中SFN含量为139.7和171.4μg/g,分别是野生型细胞系SFN含量的1.79倍和2.19倍,差异极显著(**P<0.01);B-C-E基因过表达细胞系SFN含量是BCAT4基因过表达细胞系的1.23倍,差异显著(*P<0.05)。而CYP79F1和ESM1过表达细胞系未检测到高于对照的SFN含量。综上所述,单基因BCAT4的过表达对SFN含量的影响大于CYP79F1与ESM1。多基因串联共表达对SFN含量的影响效果好于单个基因的过表达。     

青花菜萝卜硫素合成相关基因BoCYP83A1的克隆与表达分析

CYP83A1基因是萝卜硫素合成代谢中的关键基因,该试验以青花菜品种CDBY-10为材料,利用RACE和RT-PCR方法,获得BoCYP83A1基因的全长序列。该基因全长1 509bp,编码502个氨基酸,包含保守的P450结构域。通过实时荧光定量PCR分析了BoCYP83A1基因在不同品种、不同组织以及不同激素处理下的表达水平。系统进化树分析表明,BoCYP83A1与结球甘蓝亲缘关系最近。BoCYP83A1基因在不同品种间的组织特异性不同:在青花菜品种CDBY-10的根、茎、叶3个组织间表达水平差异较小,在品种CDBY-12中表现为茎叶根,在CDBY-14中则表现为根茎叶。MeJA及SA处理均能够引起BoCYP83A1基因表达量的变化:经MeJA处理后,BoCYP83A1基因表达量升高至对照的1.9倍,而后有少量下降;经SA处理后,BoCYP83A1基因表达水平迅速降低,在6h时降低至对照的0.1倍,而后逐渐回升至对照的表达水平。研究表明,BoCYP83A1基因在不同青花菜品种中的表达特性不同,其表达能够被MeJA和SA所调控。青花菜BoCYP83A1的克隆及鉴定为培育高萝卜硫素含量的青花菜新品种奠定了理论基础。     

硒性白内障大鼠模型晶状体中GR和GSH-Px的表达

 为探讨硒性白内障大鼠晶状体中谷胱甘肽过氧化物酶 (GSH Px)和谷胱甘肽还原酶 (GR)的活性调节在硒性白内障形成中的作用及调节方式 ,采用半定量RT PCR方法 ,比较正常晶状体、核中心混浊晶状体 (核白 )和完全混浊晶状体 (全白 )中GSH Px和GR的mRNA水平及酶活性的变化 .研究发现 ,核白晶状体中 2种酶的活性和mRNA水平均升高 ,其中酶活性的升高幅度小于mRNA水平 .随着白内障的发展 ,2种酶的活性和mRNA水平均逐渐下降 .至晶状体全白时 ,2种酶的活性均显著低于正常 ;全白时GR的mRNA水平降至正常 ,GSH Px的mRNA水平则仍高于正常 .结果表明 ,硒性白内障形成与细胞内GSH Px和GR的活性调节密切相关 ,GSH Px和GR的活性调节可能主要发生在转录水平     

Sodium Selenite Improves Folliculogenesis in Radiation-Induced Ovarian Failure: A Mechanistic Approach

Radiotherapy is a major factor contributing to female infertility by inducing premature ovarian failure (POF). Therefore, the need for an effective radioprotective agent is evident. The present study investigated the mechanism of potential radioprotective effect of sodium selenite on radiation-induced ovarian failure and whether sodium selenite can stimulate in-vivo follicular development in experimental rats. Immature female Sprague-Dawely rats were either exposed to gamma-radiation (3.2 Gy, LD₂₀), once and/or treated with sodium selenite (0.5 mg/kg), once daily for one week before irradiation. Follicular and oocyte development, apoptotic markers, proliferation marker as well as oxidative stress markers were assessed 24-h after irradiation. In addition, fertility assessment was performed after female rats became completely mature at two months of age. Sodium selenite significantly enhanced follicular development as compared to the irradiated group. Sodium selenite significantly reversed the oxidative stress effects of radiation that was evidenced by increasing in lipid peroxide level and decreasing in glutathione level, and glutathione peroxidase (GPx) activity. Assessment of apoptosis and cell proliferation markers revealed that caspase 3 and cytochrome c expressions markedly-increased, whereas, PCNA expression markedly-decreased in the irradiated group; in contrast, sodium selenite treatment prevented these alterations. Histopathological examination further confirmed the radioprotective efficacy of sodium selenite and its in-vivo effect on ovarian follicles’ maturation. In conclusion, sodium selenite showed a radioprotective effect and improved folliculogenesis through increasing ovarian granulosa cells proliferation, estradiol and FSH secretion, and GPx activity, whilst decreasing lipid peroxidation and oxidative stress, leading to inhibition of the apoptosis pathway through decreasing the expressions of caspase 3 and cytochrome c.     

Selenocysteine in proteins-properties and biotechnological use

Selenocysteine (Sec), the 21st amino acid, exists naturally in all kingdoms of life as the defining entity of selenoproteins. Sec is a cysteine (Cys) residue analogue with a selenium-containing selenol group in place of the sulfur-containing thiol group in Cys. The selenium atom gives Sec quite different properties from Cys. The most obvious difference is the lower pK(a) of Sec, and Sec is also a stronger nucleophile than Cys. Proteins naturally containing Sec are often enzymes, employing the reactivity of the Sec residue during the catalytic cycle and therefore Sec is normally essential for their catalytic efficiencies. Other unique features of Sec, not shared by any of the other 20 common amino acids, derive from the atomic weight and chemical properties of selenium and the particular occurrence and properties of its stable and radioactive isotopes. Sec is, moreover, incorporated into proteins by an expansion of the genetic code as the translation of selenoproteins involves the decoding of a UGA codon, otherwise being a termination codon. In this review, we will describe the different unique properties of Sec and we will discuss the prerequisites for selenoprotein production as well as the possible use of Sec introduction into proteins for biotechnological applications. These include residue-specific radiolabeling with gamma or positron emitters, the use of Sec as a reactive handle for electophilic probes introducing fluorescence or other peptide conjugates, as the basis for affinity purification of recombinant proteins, the trapping of folding intermediates, improved phasing in X-ray crystallography, introduction of 77Se for NMR spectroscopy, or, finally, the analysis or tailoring of enzymatic reactions involving thiol or oxidoreductase (redox) selenolate chemistry.     

High Error Rates in Selenocysteine Insertion in Mammalian Cells Treated with the Antibiotic Doxycycline,Chloramphenicol, or Geneticin

Antibiotics target bacteria by interfering with essential processes such as translation, but their effects on translation in mammalian cells are less well characterized. We found that doxycycline, chloramphenicol, and Geneticin (G418) interfered with insertion of selenocysteine (Sec), which is encoded by the stop codon, UGA, into selenoproteins in murine EMT6 cells. Treatment of EMT6 cells with these antibiotics reduced enzymatic activities and Sec insertion into thioredoxin reductase 1 (TR1) and glutathione peroxidase 1 (GPx1). However, these proteins were differentially affected due to varying errors in Sec insertion at UGA. In the presence of doxycycline, chloramphenicol, or G418, the Sec-containing form of TR1 decreased, whereas the arginine-containing and truncated forms of this protein increased. We also detected antibiotic-specific misinsertion of cysteine and tryptophan. Furthermore, misinsertion of arginine in place of Sec was commonly observed in GPx1 and glutathione peroxidase 4. TR1 was the most affected and GPx1 was the least affected by these translation errors. These observations were consistent with the differential use of two Sec tRNA isoforms and their distinct roles in supporting accuracy of Sec insertion into selenoproteins. The data reveal widespread errors in inserting Sec into proteins and in dysregulation of selenoprotein expression and function upon antibiotic treatment.