Hydrogen-bond dynamics of water in presence of an amphiphile,tetramethylurea: signature of confinement-induced effects

Various experimental and simulation studies have suggested that the presence of amphiphilic molecules in aqueous solutions substantially perturbs the tetrahedral hydrogen-bond (H-bond) network of neat liquid water. Such structural perturbation is expected to impact H-bond lifetime of liquid water. Tetramethylurea (TMU) is an example of an amphiphile because it possesses both hydrophobic and hydrophilic moieties. Molecular dynamics simulations of (water+TMU) binary mixtures at various compositions have been performed in order to investigate the microscopic mechanism through which the amphiphiles influence the H-bond dynamics of liquid water at room temperature. Present simulations indicate lengthening of both water–water H-bond lifetime and H-bond structural relaxation time upon addition of TMU in aqueous solution. At the highest TMU mole fraction studied, H-bond lifetime and structural relaxation time are, respectively, ～4 and ～8 times longer than those in neat water. This is comparable with the slowing down of H-bond dynamics for water molecules confined in cyclodextrin cavities. Simulated relaxation profiles are multi-exponential in character at all mixture compositions, and simulated radial distribution functions suggest enhanced water–water and water–TMU interactions upon addition of TMU. No evidence for complete encapsulation of TMU by water H-bond network has been found.     

耐镉马克思克鲁维酵母重金属镉吸附特性的研究

菌株YS-K1是从镉污染土壤中筛选获得的一株耐镉马克思克鲁维酵母Kluyveromyces marxianus YS-K1,对其镉吸附特性研究结果表明,该菌对镉具有良好的耐受性和吸附性,即使在镉浓度高达140mg/L的培养基中也能生长,当镉浓度在30mg/L以下时,24h后能吸附溶液中90%以上的镉,且最佳吸附条件为pH6.0,温度30℃。该菌所吸附的镉大部分集中在细胞壁上,占总吸附镉的76%,细胞膜上的占9%,细胞质中的占15%;能量抑制剂2,4-二硝基苯酚(DNP)和二环己基碳二亚胺(DCC),分别能降低菌株15%和22%的镉吸附量。在Kluyveromyces marxianus YS-K1细胞中,锌离子与镉离子有共用的结合位点,锌离子不仅会与镉离子竞争细胞表面的结合位点,减少其对镉的吸附量,而且也会与镉离子竞争进入细胞的通道位点,减少其对镉的积累量,同时能部分恢复镉离子对菌株生长的抑制作用。     

Concentations of copper, Zinc, and magnesium in sera from patients with idiopathic dilated cardiomyopathy

Trace elements are known to have a key role in myocardial metabolism. The accumulation (cobalt, arsenic, copper) or deficiency (selenium, zinc) of trace elements may be responsible for idiopathic dilated cardiomyopathy. We investigated the trace element concentrations (Cu, Zn, Mg) in sera from patients with dilated cardiomyopathy by atomic absorption spectrophotometry. We observed that patients with dilated cardiomyopathies have higher copper and lower zinc concentrations in serum than healthy controls. The magnesium concentrations of patients did not differ significantly from that of control subjects.     

Mitogenomic phylogeny of the Percichthyidae and Centrarchiformes (Percomorphaceae): comparison with recent nuclear gene-based studies and simultaneous analysis

Delineation of the fish family Percichthyidae (Percomorphaceae) has a long and convoluted history, with recent morphological-based studies restricting species members to South American and Australian freshwater and catadromous temperate perches. Four recent nuclear gene-based phylogenetic studies, however, found that the Percichthyidae was not monophyletic and was nested within a newly discovered inter-familial clade of Percomorphaceae, the Centrarchiformes, which comprises the Centrarchidae and 12 other families. Here, we reexamined the systematics of the Percichthyidae and Centrarchiformes based on new mitogenomic information. Our mitogenomic results are globally congruent with the recent nuclear gene-based studies although the overall amount of phylogenetic signal of the mitogenome is lower. They do not support the monophyly of the Percichthyidae, because the catadromous genus Percalates is not exclusively related to the freshwater percichthyids. The Percichthyidae (minus Percalates) and Percalates belong to a larger clade, equivalent to the Centrarchiformes, but their respective sister groups are unresolved. Because all recent analyses recover a monophyletic Centrarchiformes but with substantially different intra-relationships, we performed a simultaneous analysis for a character set combining the mitogenome and 19 nuclear genes previously published, for 22 centrarchiform taxa. This analysis furthermore indicates that the Centrarchiformes are divided into three lineages and the superfamily Cirrhitoidea is monophyletic as well as the temperate and freshwater centrarchiform perch-like fishes. It also clarifies some of the relationships within the freshwater Percichthyidae.     

Study of a lipophilic captopril analogue binding to angiotensin I converting enzyme

Human ACE is a central component of the renin–angiotensin system and a major therapeutic target for cardiovascular diseases. The somatic form of the enzyme (sACE) comprises two homologous metallopeptidase domains (N and C), each bearing a zinc active site with similar but distinct substrate and inhibitor specificities. In this study, we present the biological activity of silacaptopril, a silylated analogue of captopril, and its binding affinity towards ACE. Based on the recently determined crystal structures of both the ACE domains, a series of docking calculations were carried out in order to study the structural characteristics and the binding properties of silacaptopril and its analogues with ACE. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd.     

Protective effects of zinc on cadmium toxicity in rodents

A study of acute and subacute toxicity of cadmium ions [Cd(II)] was carried out on male Swiss mice and Sprague-Dawley rats with and without previous administration of zinc chloride. The LD₅₀ of Cd(II) as cadmium sulfate (ip) was lower in animals previously given 10 mg/kg of zinc(II) chloride (sc). Factors such as animal weight variations, biochemical parameters, and accumulation patterns of Cd(II) and Zn(II) were taken into consideration when the subacute toxicity was evaluated. Alteration of the activities of glutamic pyruvic transaminase (GPT) and of glutamic oxaloacetic transaminase (GOT) was observed in short-term-exposure (<6 h) cases. These alterations reverted to normal after 1 wk. The activity of alkaline phosphatase (ALP) and the concentrations of cholesterol and triglycerides in serum are also changed, especially so in the groups given CdSO₄ alone. In the experimental groups treated with ZnCl₂ prior to administration of cadmium, proteinuria was detected 5 wk after the treatment. Also at 5 wk, both Zn-treated and nontreated groups showed an abnormally low liver mass with respect to total body mass. Both Cd and Zn are retained preferentially in the liver but show also in the kidneys. If CdSO₄ and ZnCl₂ are given simultaneously, especially after 1 wk of treatment, Cd is accumulated in greater amounts in these organs when compared to the groups given only cadmium sulfate.     

滇苦菜（Picris divaricata Vant.）对锌的吸收和富集特性

通过野外调查和营养液培养,研究Zn对滇苦菜(Picris divaricata Vant.)生长的影响及其吸收富集Zn的特性.野外调查发现,铅锌矿区土壤Zn全量范围为1724～134973 mg·kg-1,平均为61495 mg·kg-1.滇苦菜地上部Zn含量范围为1214～18339 mg·kg-1,平均为5911 mg·kg-1,且转运系数(S/R)的平均值为2.21,大于1.在营养液培养条件下,当Zn浓度达到80 mg·L-1时,滇苦菜生长开始出现明显的中毒症状,随着Zn处理的增加,植物地上部与根部的生物量呈下降趋势,Zn含量呈上升趋势,且地上部与根部在160 mg·L-1时Zn含量达最高值,分别为12472 mg·kg-1和14026 mg·kg-1,体内Zn富集量也达最高值1518 μg ·株-1,并且整个植株富集的Zn有75%～91%分布在地上部.结果表明滇苦菜具有很强的忍耐、吸收和富集Zn的能力,是我国境内发现的又一种Zn超富集植物.     

水稻与拟南芥PHD-finger蛋白的系统分析

PHD-finger(plant homeodomain finger)是具Cys4-His-Cys3特征结构的锌指蛋白结构域,它广泛存在于植物或动物转录调节蛋白中。此类蛋白在植物或动物蛋白质组中具有多个功能各异的家族成员,并在发育中扮演重要的角色。鉴定了水稻44个推定的非冗余PHD-finger蛋白,并与拟南芥蛋白质组中45个该家族成员进行了比较;所构建的2棵进化树涵盖了这89个蛋白质,暗示水稻、拟南芥与人的PHD-finger蛋白中存在共同祖先。