Structure of a Na+/H+ antiporter and insights into mechanism of action and regulation by pH

The control by Na+/H+ antiporters of sodium/proton concentration and cell volume is crucial for the viability of all cells. Adaptation to high salinity and/or extreme pH in plants and bacteria or in human heart muscles requires the action of Na+/H+ antiporters. Their activity is tightly controlled by pH. Here we present the crystal structure of pH-downregulated NhaA, the main antiporter of Escherichia coli and many enterobacteria. A negatively charged ion funnel opens to the cytoplasm and ends in the middle of the membrane at the putative ion-binding site. There, a unique assembly of two pairs of short helices connected by crossed, extended chains creates a balanced electrostatic environment. We propose that the binding of charged substrates causes an electric imbalance, inducing movements, that permit a rapid alternating-access mechanism. This ion-exchange machinery is regulated by a conformational change elicited by a pH signal perceived at the entry to the cytoplasmic funnel.     

串叶松香草根细胞中的膜状溶酶体

用透射电镜对串叶松香草根细胞进行观察，发现在细胞中普遍存在膜状溶酶体，其内具有被分解消化的细胞质结构．并对这一现象进行了初步分析．     

Genetic diversity and chloroquine selective sweeps in Plasmodium falciparum

Widespread use of antimalarial agents can profoundly influence the evolution of the human malaria parasite Plasmodium falciparum. Recent selective sweeps for drug-resistant genotypes may have restricted the genetic diversity of this parasite, resembling effects attributed in current debates to a historic population bottleneck. Chloroquine-resistant (CQR) parasites were initially reported about 45 years ago from two foci in southeast Asia and South America, but the number of CQR founder mutations and the impact of chlorquine on parasite genomes worldwide have been difficult to evaluate. Using 342 highly polymorphic microsatellite markers from a genetic map, here we show that the level of genetic diversity varies substantially among different regions of the parasite genome, revealing extensive linkage disequilibrium surrounding the key CQR gene pfcrt and at least four CQR founder events. This disequilibrium and its decay rate in the pfcrt-flanking region are consistent with strong directional selective sweeps occurring over only approximately 20-80 sexual generations, especially a single resistant pfcrt haplotype spreading to very high frequencies throughout most of Asia and Africa. The presence of linkage disequilibrium provides a basis for mapping genes under drug selection in P. falciparum.     

碳源、pH值和温度对脱氮菌株脱氮性能的影响

考查碳源(醋酸钠、柠檬酸钠、葡萄糖、甘油、糖蜜、甲醇和蔗糖)、pH值和温度这3个条件对脱氮菌株HN18脱氮能力的影响.结果显示:以糖蜜作为碳源不但使菌株HN18对氨氮、硝酸盐氮的去除率高,亚硝酸盐氮的积累量少,而且价格低、原材料来源广泛,能得到较高的经济效益;菌株HN18生长和脱氮的最适pH值为7.5,最适温度为30℃.     

冻融作用对土壤含水率、pH值、电导率的影响

我国对土壤冻融作用研究主要集中在自然环境条件下冻土环境变化。文章对齐齐哈尔市南郊污水处理厂附近的氧化塘中的冻融土壤进行研究,论述了冻融作用对土壤三参数的影响。研究表明,季节性冻融作用对土壤的含水率、pH值、电导率都有影响,尤其是对含水率的影响较大。     

pH Dependence of Chlorophyll States, Protein Structures and Function of the PSII Membranes

IntroductionPhotosystem II ( PSII) is a pigment- proteincomplex in the thylakoid membrane. Its reactioncenter( PSII- RC) ,which is composed of D1 andD2 proteins,generates the highly positive oxidantrequired for the oxidation of water by light- drivencharge separation. Water oxidation occurs at theMn4cluster positioned atthe center of the oxygen-evolving complex on the lumenal surface of PSII.In green plants,the highly reactive Mn4cluster isshielded by a number of extrinsic proteins( 33…     

不同培养基、温度、光照及pH值对卵形隐藻生长的影响

从5种培养基中筛选到较适合卵形隐藻生长的改良BBM及FPW培养液,采用梯度法、正交试验法分别研究温度、光照强度、光照周期、pH值对卵形隐藻生长的影响．结果表明,温度25℃,光照强度6000lx,光照周期18(光照)：16(黑暗),pH7．0较有利于卵形隐藻的生长．使用改良BBM培养液培养的卵形隐藻对高温有较强的耐受性;FPW培养液由于配方简单以及用池水配制的特点更适于隐藻的规模化培养。     

论力、能量和熵的概念在基础物理中的作用

从统一的角度,历史性地论述了力、能量和熵三个物理量的中心地位,探讨了它们在基础物理中的意义.修正了Prigogine总熵变公式,引入了k因子和g因子,调解热寂说和进化论的关系,并据此从熵的角度分析分子自组织进化熵减少的机理.最后分析了力、能量和熵之间的相互关系,指出从力、能量到熵概念标志着物理学从"存在的物理学"发展到"演化的物理学".     

储藏过程中鲜乳中的细菌数、pH、酸度的变化

采用标准平板计数法测定牛乳的细菌数、酸度计法测定牛乳的pH值、滴定法测定牛乳的酸度,通过设置不同储藏温度:常温(不避光)、4℃,-18℃对鲜乳进行储藏,每隔一定时间测定不同储藏条件下鲜乳中细菌数、酸度、pH的值,得出储藏过程中细菌数、酸度、pH值的变化规律,找出各温度储藏条件下最佳储藏时间以及最佳储藏温度.研究表明:鲜...     

决策与图书馆的作用

本文在论述决策与信息之关系的基础上,说明强化图书馆的情报职能,发挥其决策服务的优势和“智囊团”的巨大作用,是科学决策和社会主义事业取得成功的重要保证。