A Preliminary Study on the Structure and Function of the Vascular Transfer Cells in Garlic Scape

The vascular transfer cells in garlic scape havebeen examined with electron microscope. Their structure, distributive feature and adenosine triphosphatase (ATPase) activity are studied. The mature vascular transfer cells exhibit the characteristic cell wall ingrowths. The cell contents include a large nucleus, dense cytoplasm and various normal organelles. It is notable that there are numerous mitochondria with well developed, cristae. Plasmodesmata are extensively present in the wall, and transfer cells are connected to adjacent cells by them. The senescing transfer cells become more vacuolated and have a large central vacuole and dense parietal cytoplasm. Their wall ingrowths seem to degenerate and finally disappear. The transfer cells show a particular pattern of distribution in the vascular bundle of the garlic scape. Some of them are present between the vessels of xylem and the sieve tubes of phloem. However, more abundant cell wall ingrowths occur on those walls which abut on, or are close to the vessel of xylem. The other transfer cells are located between the sieve tubes and parenehyma cells. The phloem transfer cell which is adjacent to sieve tube has developed from companion cell. All the transfer cells are mainly concerned with the loading and unloading of sieve tubes. And they may play an important role in facilitating intensive material transfer between two independent systems (i.e. the vessels and sieve tubes, the symplast and apoplast). The results of the cytochemical localization of ATPase using a lead precipitation technique exhibit strong enzyme activity on the plasmalemma of the transfer cells. It is suggested that the transfer cells are especially active in solute movement through them to which cellular energy metabolism coupled.     

Mass transfer in fermentation

An essential consideration in the design and operation of commercial fermenters is to ensure adequate mass transfer. The complex composition of fermentation liquids makes it difficult to predict accurately the mass transfer characteristics in large vessels. Here various aspects of mass transfer are discussed and their relationships examined. Strategies for predicting the most important type of mass transfer — between gases and liquids — in large scale fermentations are presented.     

基于酿酒酵母的大片段DNA组装与转移技术进展*

DNA组装与转移技术是合成生物学的核心使能技术之一,生命体设计改造的复杂度不断提升,使得对大片段DNA组装与转移技术的需求也日益旺盛。小片段DNA的组装与转移技术目前已经比较成熟,大片段DNA由于其分子量大、易断裂,使得体外操作繁琐且效率低下。聚焦酿酒酵母体内组装和转移的技术进展,详细介绍了基于酿酒酵母一次组装和迭代组装的不同方法,并从导入与导出的角度介绍了大片段DNA的转移技术,便于研究者更好地理解和选择酿酒酵母体内组装与转移技术。此外,还展望了将酿酒酵母开发为大片段DNA组装与转移通用平台实现更多物种基因组大尺度设计改造的愿景。     

Stimulated and co-operative electron transfer in energy conversion and catalysis.

A new mechanism of electron transfer, stimulated electron transfer, is postulated, in which an electronic feedback is drastically increasing both the rate of electron transfer and the propagation of free energy along electron transferring molecular pathways. In principle, the idea of pushing a system far from equilibrium to achieve a high reaction rate and co-operative phenomena is applied to molecular electron transfer. The effect is calculated from a semiclassical kinetic model of a chain redox reaction with autocatalytic feedback on individual rate constants, where the steps have subsequently been minimized to obtain a continuous electron transfer pathway with electronic feedback. The influence of inhomogeneities and asymmetries in the electron transfer path and of vectorial components (electrical field, gradient of redox potential) are discussed as well as the acceleration of individual and multiple electron transfer as a function of feedback. Examples of autocatalytic feedback are provided including mechanisms involving electron transfer proteins and multi-centre electron transfer catalysts. Such a phenomenon can be described for molecular and interfacial electron transfer in analogy to stimulated and coherent light emission. The results suggest that autocatalytic or stimulated electron transfer may be a key to the understanding of efficient electron transfer and co-operative multi-electron transfer catalysis in biology and a challenge for fuel production mechanisms in artificial photosynthesis and fuel cycles.     

Mechanisms for regulating electron transfer in multi-centre redox proteins.

Protein-mediated electron transfer is a key process in nature. Many of the proteins involved in such electron transfers are complex and contain a number of redox-active cofactors. The very complexity of these multi-centre redox proteins has made it difficult to fully understand the various electron transfer events they catalyse. This is sometimes because the electron transfer steps themselves are gated or coupled to other processes such as proton transfer. However, with the molecular structures of many of these proteins now available it is possible to probe these electron transfer reactions at the molecular level. It is becoming apparent that many of these multi-centre redox proteins have rather subtle and elegant ways for regulating electron transfer. The purpose of this article is to illustrate how nature has used different approaches to control electron transfer in a number of different systems. Illustrative examples include: thermodynamic control of electron transfer in flavocytochromes b(2) and P450 BM3; a novel control mechanism involving calmodulin-binding-dependent electron transfer in neuronal nitric oxide synthase; the probable gating of electron transfer by ATP hydrolysis in nitrogenase; conformational gating of electron transfer in cytochrome cd(1); the regulation of electron transfer by protein dynamics in the cytochrome bc(1) complex; and finally the coupling of electron transfer to proton transfer in cytochrome c oxidase.     

A genetic model for pathogenicity in Agrobacterium and for tumour induction in plants.

It is proposed that there are two transfer factors in Agrobacterium, both part of a circular chromosome, as in Rhizobium. Pathogenicity depends on the presence of one or other of these transfer factors. There is a close genetic linkage between one transfer factor and the gene for octopine metabolism; the other transfer factor is closely linked to two genes, one for nopaline metabolism and the other for sensitivity to bacteriocin 84. The transfer factors can transfer DNA from a pathogenic donor bacterium: (a) to a plant cell, converting it to a tumour cell or (b) to a non-pathogenic recipient, converting it to pathogenicity.     

Energy of the transmembrane DNA transfer in bacteria

The natural transmembrane DNA transfer in the course of the genetic transformation, transfection and conjugation is analyzed as well as the inducible transmembrane transfer affected by the different physicochemical factors. Different models for the transfer are discussed. Special attention is paid to the energetic aspects of the transfer.     

Evolution of gene transfer in bacteria

The transfer of genetic information by transformation, conjugation and transduction in bacteria occurs frequently in nature. These diverse gene transfer mechanisms in bacteria are the result of evolution and are not linked to reproduction as in eukaryotic organisms. In this review, gene transfer in bacteria will be considered from an evolutionary perspective.     

Task-partitioned nectar transfer in stingless bees: work organisation in a phylogenetic context

Abstract 1. The eusocial corbiculate bee tribes comprise the Apini (honey bees), Bombini (bumble bees), and Meliponini (stingless bees). Honey bee foragers ( Apis ) transfer nectar to receiver bees within the nest. This is an example of task partitioning, in which a task is split into sub-tasks connected by material transfer. Nectar transfer does not occur in Bombini. Although it is reported in some species of Meliponini, it has not been subject to detailed study.
2. Nectar transfer was investigated in five genera of Meliponini from Yucatan, Mexico ( Melipona , Trigona , Scaptotrigona , Nannotrigona , and Plebeia ). Nectar transfer occurred in all species and for > 99% of foragers. Multiple transfer, in which a forager unloads nectar to more than one receiver, occurred but at a lower level than in Apis . In M. beecheii , multiple transfer was associated strongly with putative recruitment dances.
3. The data provide some support for the hypothesis that task partitioning is favoured by large colony size, in that the Meliponini never have small colonies because colonies are swarm founded. This ensures that colonies are always large enough to prevent delays in finding a transfer partner imposing high costs. Further tests of this hypothesis are suggested.
4. Viewed in a phylogenetic context, the most parsimonious interpretation is that nectar transfer evolved once in the clade (Apini + Meliponini).     

A metabolic derivation of tritium transfer coefficients in animal products

Tritium is a potentially important environmental contaminant originating from the nuclear industry, and its behaviour in the environment is controlled by that of hydrogen. Animal food products represent a potentially important source of tritium in the human diet and a number of transfer coefficient values for tritium transfer to a limited number of animal products are available. In this paper we present an approach for the derivation of tritium transfer coefficients which is based on the metabolism of hydrogen in animals. The derived transfer coefficients separately account for transfer to and from free (i.e. water) and organically bound tritium. A novel aspect of the approach is that tritium transfer can be predicted for any animal product for which the required metabolic input parameters are available. The predicted transfer coefficients are compared to available independent data. Agreement is good (R ²=0.97) with the exception of the transfer coefficient for transfer from tritiated water to organically bound tritium in ruminants. This may be attributable to the particular characteristics of ruminant digestion. We show that tritium transfer coefficients will vary in response to the metabolic status of an animal (e.g. stage of lactation, diet digestibility etc.) and that the use of a single transfer coefficient from diet to animal product is inappropriate. It is possible to derive concentration ratio values from the estimated transfer coefficients which relate the concentration of tritiated water and organically bound tritium in an animal product to their respective concentrations in the animals diet. These concentration ratios are shown to be less subject to metabolic variation and may be more useful radioecological parameters than transfer coefficients. For tritiated water the concentration ratio shows little variation between animal products ranging from 0.59 to 0.82. In the case of organically bound tritium the concentration ratios vary between animal products from 0.15 (goat milk) to 0.67 (eggs). Received: 28 May 2001 / Accepted: 20 August 2001     

Directions in gene therapy

Retroviral mediated gene transfer has proven to be an effective method of transferring genetic material into many different mammalian cells. Presented in this short review is a history of retroviral-mediated gene transfer as it relates to hematopoietic- and blood-derived cells. Gene transfer into mouse, primate, and fetal sheep and primate hematopoietic stem cells is discussed. Gene transfer into lymphocytes, in particular tumor-infiltrating lymphocytes, is also addressed. The use of such lymphocytes in ongoing and submitted clinical protocols utilizing retroviral-mediated gene transfer are presented.     

试论公立医院公益性发挥与卫生财政转移支付制度改革

论述了卫生财政投入和卫生财政转移支付的现状,结合公立医院公益性的现状,分析了当前卫生投入存在的问题,提出了增强公立医院公益性的卫生财政转移支付的政策建议：制定财政转移支付制度的远景规划,调整卫生财政转移支付的模式,加大对地方财政转移支付力度,合理划分事权并明确财权,改进并优化卫生财政转移支付制度,从而为公立医院发挥公益性提供有力的财政保障。     

动物克隆中的端粒和端粒酶

端粒是染色体上的一种重要结构,对维持染色体的稳定性起重要作用。核移植后,端粒长度和端粒酶活性的变化是重要的核重编程事件。不同种类的动物和供体细胞核移植后,在端粒长度的变化上存在一些差异,反映了重编程程度的不同。核移植后,在克隆囊胚中存在高水平的端粒酶活性,克隆动物的端粒长度延长,可能是由于克隆过程中端粒酶基因的重编程的缘故。     

Phospholipid transfer proteins in microorganisms

Phospholipid transfer activity has been demonstrated in cell lysates of Saccharomyces cerevisiae, Rhodopseudomonas sphaeroides and Bacillus subtilis, and proteins facilitating phospholipid transfer from the first two organisms have recently been purified. The phospholipid transfer protein from S. cerevisiae has mol. wt. 35 000 with a specificity of transfer for phosphatidylinositol and phosphatidylcholine. The purified phospholipid transfer protein from R. sphaeroides has mol. wt. 27 000 and, although it has the ability to transfer all phospholipid species tested it displays a preference for phosphatidylglycerol. The cellular levels of phospholipid transfer activity in both S. cerevisiae and R. sphaeroides are not strictly related to the level of subcellular membranes. However, in photosynthetically grown R. sphaeroides, the distribution of the activities between soluble and membrane-associated forms is correlated with the level of intracytoplasmic membrane (a postulated membrane substrate).     

The role of cellular proliferation in the induction of experimental autoimmune thyroiditis (EAT) in mice

Experimental autoimmune thyroiditis (EAT) can be induced in susceptible strains of mice by injection of mouse thyroglobulin (MTg) and adjuvant. Lymphocytes from immunized mice develop a proliferative response to MTg which generally correlates with the development of EAT. We utilize a cell transfer system wherein spleen cells from CBA/J mice primed with MTg and lipopolysaccharide (LPS) in vivo are activated by culture with MTg in vitro to transfer EAT to naive recipients. In vivo priming of CBA/J mice is required to develop an antigen specific proliferative response to MTg. This response is optimal between 48 and 90 hr of culture at an MTg concentration of 125-250 micrograms/ml. The correlation between proliferation and transfer of EAT is not absolute as primed Balb/c X CBA/J F1 and AKR lymphocytes do not proliferate detectably in response to MTg but can be activated to transfer EAT; primed Balb/c lymphocytes neither proliferate nor transfer EAT. Proliferation per se is not sufficient to activate cells to transfer EAT as culture with nonspecific mitogens is not effective in activating primed CBA/J spleen cells to transfer EAT. However, lymphoblasts generated during in vitro culture of primed CBA/J spleen cells with MTg are responsible for transfer of EAT; small lymphocytes are ineffective. We conclude that antigen specific proliferation in response to MTg is essential in activating lymphocytes in vitro to transfer EAT.     

Energy transfer in photosynthesis

A theoretical model is presented to account for the physical mechanism of energy transfer from antenna molecules to the reaction centers in photosynthesis. The energy transfer is described by a generalized transport equation or “master equation”. The solution of this equation for the proposed model gives a relationship between the antennae interaction energy and the transfer rate. The results are shown to be in agreement with inter-antenna transfer rates calculated from experimental fluorescence lifetimes. Previous theories were based either on the Förster mechanism, which is valid for very small interaction energies, or an exciton model valid for very large interactions, but experimental results seemed to indicate that the actual situation was intermediate between these two. The Förster theory and the exciton model are limiting cases of the master equation.     

Electron-conformation transitions in the complex of bacterial photosynthetic reaction centers with cytochromes

A theoretical model of conformation--regulated electron transfer from multihaem cytochrome c to bacteriochlorophyll of the reaction centre (RC) is considered. The theoretical data are compared with the experimental ones on the basis of temperature dependence of laser-induced electron transfer from high-potential cytochrome Ch bacheriochlorophyll of RC in Ectothiohodospira shaposhnikovii chromatophores. From this comparison there were calculated the thermodynamic characteristics of cytochrome Ch transfer from the configuration without electron transfer to RC bacteriochlorophyll into the coordinated configuration with an effective transfer. The values obtained are: H = 7,1 kJ/M; S = --(30,2--36,9) J/grad. M. Possible regulatory role of such conformation transitions is discussed.     

Gene transfer and gene mapping in mammalian cells in culture

The ability to transfer mammalian genes parasexually has opened new possibilities for gene mapping and fine structure mapping and offers great potential for contributing to several aspects of mammalian biology, including gene expression and genetic engineering. The DNA transferred has ranged from whole genomes to single genes and smaller segments of DNA. The transfer of whole genomes by cell fusion forms cell hybrids, which has promoted the extensive mapping of human and mouse genes. Transfer, by cell fusion, of rearranged chromosomes has contributed significantly to determining close linkage and the assignment of genes to specific chromosomal regions. Transfer of single chromosomes has been achieved utilizing microcells fused to recipient cells. Metaphase chromosomes have been isolated and used to transfer single-to-multigenic DNA segments. DNA-mediated gene transfer, simulating bacterial transformation, has achieved transfer of single-copy genes. By utilizing DNA cleaved with restriction endonucleases, gene transfer is being empolyed as a bioassay for the purification of genes. Gene mapping and the fate of transferred genes can be examined now at the molecular level using sequence-specific probles. Recently, single genes have been cloned into eucaryotic and procaryotic vectors for transfer into mammalian cells. Moreover, recombinant libraries in which entire mammalian genomes are represented collectively are a rich new source of transferable genes. Methodology for transferring mammalian genetic information and applications for mapping mammalian genes is presented and prospects for the future discussed.     

The coupling of structural fluctuations to hydride transfer in dihydrofolate reductase

The energy barrier for hydride transfer in wild-type G121V and G121S variants of Escherichia coli dihydrofolate reductase (DHFR) fluctuates in a time-dependent manner. This fluctuation may be attributed to structural changes in the protein that modulate the site of chemistry. Despite being far from the active site, mutations at position 121 of DHFR reduce the hydride transfer rate of the enzyme. This occurrence has been suggested to arise from modifications to the conformational ensemble of the protein. We elucidate the effects of the G121S and G121V mutations on the hydride transfer barrier by identifying structural changes in the protein that correlate with lowered barriers. The effect of these structural parameters on the hydride transfer barrier may be rationalized by simple considerations of the geometric constraints of the hydride transfer reaction. Fluctuations of these properties are associated with specific backbone dihedral angles of residues within the Methione-20 (M20) loop. The dihedral angle preferences are mediated by interactions with the region of the enzyme in the vicinity of residue 121 and are translated into distinct ligand conformations. We predict mutations within the M20 loop that may alter the conformational space explored by DHFR. Such mutational changes are anticipated to adjust the hydride transfer efficacy of DHFR by modifying equilibrium distributions of hydride transfer barriers found in the enzyme.     

The lung lamellar body as a functioning membrane in protein-catalyzed phosphatidylcholine transfer

Lung lamellar bodies and liver mitochondria were used to demonstrate that soluble phospholipid transfer proteins from lung transfer phosphatidylcholine to both of these acceptors. The initial rate of transfer to lung lamellar bodies is about half that of the rate of transfer to the liver mitochondria when both acceptor membranes are present at saturating concentrations. Phosphatidylcholine unilamellar vesicles were used to demonstrate that the fatty acyl composition of the membrane phosphatidylcholine is a significant determinant of the rate of phosphatidylcholine transfer catalyzed by these proteins. The lamellar bodies have a unique phosphatidylcholine composition, and these studies suggest that this is an important factor in determining the lower initial rate of transfer to lamellar bodies. The studies have also characterized two phospholipid transfer proteins in rat lung in terms of isoelectric point. Isoelectric points for the two proteins which transfer phosphatidylcholine were found to be 5.6 ± 0.08 and 6.2 ± 0.03.