Active transport of Ca2+ by an artificial photosynthetic membrane

Transport of calcium ions across membranes and against a thermodynamic gradient is essential to many biological processes, including muscle contraction, the citric acid cycle, glycogen metabolism, release of neurotransmitters, vision, biological signal transduction and immune response. Synthetic systems that transport metal ions across lipid or liquid membranes are well known, and in some cases light has been used to facilitate transport. Typically, a carrier molecule located in a symmetric membrane binds the ion from aqueous solution on one side and releases it on the other. The thermodynamic driving force is provided by an ion concentration difference between the two aqueous solutions, coupling to such a gradient in an auxiliary species, or photomodulation of the carrier by an asymmetric photon flux. Here we report a different approach, in which active transport is driven not by concentration gradients, but by light-induced electron transfer in a photoactive molecule that is asymmetrically disposed across a lipid bilayer. The system comprises a synthetic, light-driven transmembrane Ca2+ pump based on a redox-sensitive, lipophilic Ca2+-binding shuttle molecule whose function is powered by an intramembrane artificial photosynthetic reaction centre. The resulting structure transports calcium ions across the bilayer of a liposome to develop both a calcium ion concentration gradient and a membrane potential, expanding Mitchell's concept of a redox loop mechanism for protons to include divalent cations. Although the quantum yield is relatively low (approximately 1 per cent), the Ca2+ electrochemical potential developed is significant.     

Sequence of Plasmodium falciparum chromosomes 2, 10, 11 and 14

The mosquito-borne malaria parasite Plasmodium falciparum kills an estimated 0.7-2.7 million people every year, primarily children in sub-Saharan Africa. Without effective interventions, a variety of factors-including the spread of parasites resistant to antimalarial drugs and the increasing insecticide resistance of mosquitoes-may cause the number of malaria cases to double over the next two decades. To stimulate basic research and facilitate the development of new drugs and vaccines, the genome of Plasmodium falciparum clone 3D7 has been sequenced using a chromosome-by-chromosome shotgun strategy. We report here the nucleotide sequences of chromosomes 10, 11 and 14, and a re-analysis of the chromosome 2 sequence. These chromosomes represent about 35% of the 23-megabase P. falciparum genome.     

A cat cloned by nuclear transplantation

Sheep, mice, cattle, goats and pigs have all been cloned by transfer of a donor cell nucleus into an enucleated ovum, and now we add the successful cloning of a cat (Felis domesticus) to this list. However, this cloning technology may not be readily extendable to other mammalian species if our understanding of their reproductive processes is limited or if there are species-specific obstacles.     

An eSnake model for medical image segmentation

Deformable model is a curve or a surface drivenpartial differential equations (PDE) method for imagesegmentation and pattern recognition. Two types ofdeformable models have been developed previously.One is the parametric deformable model proposed byKass et al.[1], which formulates the curve explicitlyin the parametric form. The other is the geometricdeformable model, which implicitly characterizes thecurve by a level set function developed by Osher,Sethian and implement…     

水平注水井与直井联合井网见水时间研究

为了寻求一种简单、有效的计算水平注水井与直井联合井网的见水时间的方法,将水平井简化为具有等效井筒半径的直井,考虑水平井与直井联合布井水驱油的非活塞性,运用等值渗流阻力法将渗流区划分为3个阻力区,推导出了五点法、七点法和九点法水平井与直井联合井网的油井见水时间的计算公式和修正公式。计算结果表明,井网的见水时间随水平井长度的增加而缩短;相同的井距和生产条件下,五点法井网的见水时间要长于九点法和七点法井网;随水平井与水平方向夹角的增大,五点法井网的见水时间缩短,七点法井网的见水时间先增加后缩短,九点法井网的见水时间增加;油藏和流体参数对井网见水时间影响不大。     

赤霉素A环重排反应催化剂研究

 简介了赤霉素A环的重排反应,即1,2位及1,10位之间双键的移动及相应内酯环的重排.在利用重排反应构建赤霉素A环的1,2位双键时,首次发现商品化试剂苯基二氯化硼与二苯基溴化硼及二甲基溴化硼一样可用于催化此反应.