Oxidative damage to 5-methylcytosine in DNA.

Exposure of pyrimidines of DNA to ionizing radiation under aerobic conditions or oxidizing agents results in attack on the 5,6 double bond of the pyrimidine ring or on the exocyclic 5-methyl group. The primary product of oxidation of the 5,6 double bond of thymine is thymine glycol, while oxidation of the 5-methyl group yields 5-hydroxymethyluracil. Oxidation of the 5,6 double bond of cytosine yields cytosine glycol, which decomposes to 5-hydroxycytosine, 5-hydroxyuracil and uracil glycol, all of which are repaired in DNA by Escherichia coli endonuclease III. We now describe the products of oxidation of 5-methylcytosine in DNA. Poly(dG-[3H]dmC) was gamma-irradiated or oxidized with hydrogen peroxide in the presence of Fe3+ and ascorbic acid. The oxidized co-polymer was incubated with endonuclease III or 5-hydroxymethyluracil-DNA glycosylase, to determine whether repairable products were formed, or digested to 2'-deoxyribonucleosides, to determine the total complement of oxidative products. Oxidative attack on 5-methylcytosine resulted primarily in formation of thymine glycol. The radiogenic yield of thymine glycol in poly(dG-dmC) was the same as that in poly(dA-dT), demonstrating that 5-methylcytosine residues in DNA were equally susceptible to radiation-induced oxidation as were thymine residues.     

组胺对培养新生大鼠心肌细胞自发性搏动及动作电位的影响

以培养大鼠乳鼠心肌细胞为模型,观察组胺对培养心肌细胞自发性搏动频率及动作电位的影响。结果表明：组胺０．１－１０ｕｍｏｌ／Ｌ可以引起剂量依赖性的心肌细胞搏动频率的增快,而且这种效应呈时间依赖性。组胺１０ｕｍｏｌ／Ｌ可以使心肌细胞动作电位的幅度（ＡＰＡ）,最大上升速率（Ｖｍａｘ）及超射（ＯＳ）明显增加,动作电位持续时间（ＡＰＤ５０和ＡＰＤ９０）明显延长,窦性周长（ＳＣＬ）明显缩短。以上结果提示,组胺致     

植物蛋白质S-亚硝基化修饰的检测与分析

S-亚硝基化是一种重要的蛋白质翻译后修饰方式, 是指一氧化氮(NO)基团共价连接至靶蛋白特定半胱氨酸残基的自由巯基, 从而形成S-亚硝基硫醇(SNO)的过程。S-亚硝基化修饰广泛存在于各有机体中, 通过改变蛋白质生化活性、稳定性、亚细胞定位以及蛋白质-蛋白质相互作用等机制而调控不同的生物学过程或信号通路。在蛋白质S-亚硝基化检测分析方法中, 最为广泛使用的是生物素转化法(biotin switch assay), 其基本原理是首先封闭未被修饰的自由巯基, 进而将被修饰的SNO基团特异地还原为自由巯基并使用生物素将其特异标记。被生物素标记的半胱氨酸残基(即被修饰位点)可进一步通过蛋白质免疫印迹和/或质谱等方法进行检测分析。该文详细描述了植物蛋白质样品的体内和体外生物素转化法的实验流程, 并对实验过程中的注意事项进行了讨论。     

用亲和层析技术分离纯化天冬氨酸酶

<正> 亲和层析技术做为现代生化实验室常用的提纯方法,具有专一性强,活力损失小,分离步骤少等优点。天冬氨酸酶是重要的酶制剂,以往见报的分离纯化工艺步骤繁琐,活力损失大。本文报道的新工艺是用聚乙二醇(PEG)/磷酸钾双水相抽提;DEAE-sophadex A-50柱层析除PEG和部分杂蛋白;环氧氯丙烷活化载体,底物作配基的亲和层析技术获得了电泳纯的天冬氨酸酶。     

草原生态学研究方法学术讨论会在成都召开

中国植物学会于1981年11月21日至27日在四川省成都市召开了有61名代表参加的草原生态学研究方法学术讨论会。大会收到包括植物群落结构调查研究、第一性生产力测定、第二性生产力测定、光合作用测定、物质与水分循环、热值测定、数学生态等有关内容的研究方法论文和报告34篇。其中有18篇论文在大会上作了报告。在小组讨论中,代表们就第一性生产力测定、水分与物质循环、光合作用测定     

Repellent,Insecticidal and Antimicrobial Activities of Leaf Essential Oils from Three Eucalyptus Species

Developing effective and eco‐friendly antimicrobials and pesticides has become a highly important issue. The repellent, insecticidal and antimicrobial activity of essential oils (EOs) isolated by hydrodistillation from dried leaves of the three Eucalyptus species (E. cloeziana, E. umbellata and E. benthamii) were investigated. During GC/MS analysis, α‐pinene (47.36 %), 1,8‐cineol (38.53 %) and α‐pinene (35.31 %) were identified as major components of E. cloeziana, E. umbellata and E. benthamii, respectively. The EOs from E. cloeziana exhibited the longest effective protection time (465 min, at 50.0 % w/w) for humans among the EOs studied. The effective protection time was 30 min and 300 min at concentrations of 12.5 % (w/w) and 25.0 % (w/w), respectively. Fumigating insecticidal activity of EOs from three Eucalyptus species was tested by airtight fumigation in conical flask, which indicated that essential oils had a highly and rapidly insecticidal activity on Culex pipiens quinquefasciatus. The antimicrobial activity of EOs was evaluated by using disc diffusion and agar dilution methods. There was no significant difference in the antibacterial activity of EOs from E. cloeziana and E. umbellate and they had the same MICs (20 mL/L) on Staphylococcus aureus, Salmonella typhi, Bacillus subtilis and Escherichia coli. E. benthamii had the worst microbial inhibitory effect among the three Eucalyptus essential oils and the MIC value for the test species is 40 mL/L except for Rhodotorula Harrison (10 mL/L).     

Double the Capacity of Manganese Spinel for Lithium‐Ion Storage by Suppression of Cooperative Jahn–Teller Distortion

The relatively low capacity and capacity fade of spinel LiMn₂O₄ (LMO) limit its application as a cathode material for lithium‐ion batteries. Extending the potential window of LMO below 3 V to access double capacity would be fantastic but hard to be realized, as it will lead to fast capacity loss due to the serious Jahn–Teller distortion. Here using experiments combined with extensive ab initio calculations, it is proved that there is a cooperative effect among individual Jahn–Teller distortions of Mn³⁺O₆ octahedrons in LMO, named as cooperative Jahn–Teller distortion (CJTD) in the text, which is the difficulty to access the capacity beyond one lithium intercalation. It is further proposed that the cationic disordering (excess Li at Mn sites and Li/Mn exchange) can intrinsically suppress the CJTD of Mn³⁺O₆ octahedrons. The cationic disordering can break the symmetry of Mn³⁺ arrangements to disrupt the correlation of distortions arising from individual JT centers and prevent the Mn³⁺? O bonds distorting along one direction. Interestingly, with the suppressed CJTD, the original octahedral vacancies in spinel LMO are activated and can serve as extra Li‐ion storage sites to access the double capacity with good reversible cycling stability in microsized LMO.     

Correction to: Development of a Novel Reverse Transcription Loop-Mediated Isothermal Amplification Method for Rapid Detection of SARS-CoV-2

Virologica Sinica - The corrected legend is given below.