DC和AC磁场混合作用下的离子运动

本文研讨了在微弱ＤＣ磁场和频率非常低的ＡＣ磁场并行作用下，位于大分子内部的离子运动情况。主要焦点是大分子中磁场对离子热运动的影响，通过一些离散频率的分析揭示了热运动的共振效应。指出当ＤＣ和ＡＣ磁场施加或切断时离子热运动能量将发生变化，如果大分子周围的媒介质的粒子能充分阻止瞬间接触，就会引起大分了子量子态的变化。     

Multiplexed Single-molecule Force Proteolysis Measurements Using Magnetic Tweezers

The generation and detection of mechanical forces is a ubiquitous aspect of cell physiology, with direct relevance to cancer metastasis¹, atherogenesis² and wound healing³. In each of these examples, cells both exert force on their surroundings and simultaneously enzymatically remodel the extracellular matrix (ECM). The effect of forces on ECM has thus become an area of considerable interest due to its likely biological and medical importance^4-7.Single molecule techniques such as optical trapping⁸, atomic force microscopy⁹, and magnetic tweezers^10,11 allow researchers to probe the function of enzymes at a molecular level by exerting forces on individual proteins. Of these techniques, magnetic tweezers (MT) are notable for their low cost and high throughput. MT exert forces in the range of ~1-100 pN and can provide millisecond temporal resolution, qualities that are well matched to the study of enzyme mechanism at the single-molecule level¹². Here we report a highly parallelizable MT assay to study the effect of force on the proteolysis of single protein molecules. We present the specific example of the proteolysis of a trimeric collagen peptide by matrix metalloproteinase 1 (MMP-1); however, this assay can be easily adapted to study other substrates and proteases.     

Magnetic sorting of leukocytes

Magnetic filtration of surface-labeled cells has been applied to the fractionation of leukocytes in a model system, using a colloidal magnetite reagent to label mouse spleen cells. This reagent was completely free from problems of aggregation or settling. Since the individual submicron particles were invisible under the microscope, cells were not visibly altered by labeling. Viability also was unaffected by either labeling or magnetic filtration. Using a 10-kG magnet and a 5-mL filter column, 50 million cells were fractionated in less than 10 min, with 99% removal of labeled T lymphocytes. The efficiency of the magnetic method is limited at present by the fact that cells that do not have the surface target antigen of interest, and so are not antibody coated, may adsorb a small amount of label nonspecifically. These then have a nonzero chance of being captured in the filter along with the labeled cells.     

磁力治疗胆石症的特征和意义

根据中国医学的经络理论和现代生物磁学的原理,发明了磁力治疗胆石症,已经有20年了.它把磁穴疗法和来源于传统的中国医学的运动疗法、食物疗法结合起来.它是以磁场为主导,5个环节紧紧相扣的疗法,5个环节是磁场主导、揉耳反射、高脂餐、排石体操和淘洗大便.疗法中有些环节可以在医生的指导下病人在家中进行.本疗法预防和治疗胆石症有很好的疗效,于1987年参加了加拿大蒙特利尔市国际发明展览会.文中讨论了磁力治疗胆石症冲刷和排出胆结石的机理.     

磁力治疗胆石症的特征和意义

根据中国医学的经络理论和现代生物磁学的原理,发明了磁力治疗胆石症,已经有20年了。它把磁穴疗法和来源于传统的中国医学的运动疗法、食物疗法结合起来。它是以磁场为主导,5个环节紧紧相扣的疗法,5个环节是磁场主导、揉耳反射、高脂餐、排石体操和淘洗大便。疗法中有些环节可以在医生的指导下病人在家中进行。本疗法预防和治疗胆石症有很好的疗效,于1987年参加了加拿大蒙特利尔市国际发明展览会。文中讨论了磁力治疗胆石症冲刷和排出胆结石的机理。     

Magnetic and structural properties of magnetite in radular teeth of chiton Acanthochiton rubrolinestus

The teeth of the Polyplacophora Chiton Acanthochiton Rubrolinestus contain biomineralized magnetite crystallites whose biological functions in relation to structure and magnetic properties are not well understood. Here, using superconducting quantum interference device (SQUID) magnetometry, we find that the saturation magnetization (σ(s)) and the Verwey transition temperature (T(v)) of tooth particles are 78.4 emu/g and 105 K, respectively. These values are below those of the stoichiometric magnetite. An in situ examination of the structure of the magnetite-bearing region within an individual tooth using high-resolution transmission electron microscopy indicates magnetite microcrystals form electron dense polycrystalline sheets with typical lengths of about 800 nm and widths of about 150 nm. These polycrystalline sheets are arranged regularly along the longitudinal direction of the tooth cutting surface. In addition, the crystallites in polycrystalline sheets take on generally good crystallinity. The magnetic microstructures of in situ magnetic force microscopy demonstrate that the [111] easy direction of magnetite microcrystals are aligned along the length of the tooth, whereas the [111] direction is parallel to the thickness of the tooth. Both M?ssbauer spectra and magnetization versus temperature measurements under field cooled and zero-field cooled conditions do not detect superparamagnetic magnetite crystallites in the mature major lateral tooth particles of this chiton.     

Motion perception and visual signal design in Anolis lizards

Anolis lizards communicate with displays consisting of motion of the head and body. Early portions of long-distance displays require movements that are effective at eliciting the attention of potential receivers. We studied signal-motion efficacy using a two-dimensional visual-motion detection (2DMD) model consisting of a grid of correlation-type elementary motion detectors. This 2DMD model has been shown to accurately predict Anolis lizard behavioural response. We tested different patterns of artificially generated motion and found that an abrupt 0.3° shift of position in less than 100 ms is optimal. We quantified motion in displays of 25 individuals from five species. Four species employ near-optimal movement patterns. We tested displays of these species using the 2DMD model on scenes with and without moderate wind. Display movements can easily be detected, even in the presence of windblown vegetation. The fifth species does not typically use the most effective display movements and display movements cannot be discerned by the 2DMD model in the presence of windblown vegetation. A number of Anolis species use abrupt up-and-down head movements approximately 10 mm in amplitude in displays, and these movements appear to be extremely effective for stimulating the receiver visual system.     

Atomic Force Microscopy of Plant-Parasitic Nematodes

A simple method for atomic force microscopy (AFM) of nematode cuticle was developed to visualize the external topography of Helicotylenchus lobus, Meloidogyne javanica, M. incognita, and Xiphinema diversicaudatum. Endospores of two isolates of the nematode parasite, Pasteuria penetrans, adhering to M. incognita and X. diversicaudatum were also visualized and measured by this technique. Scanning procedures were applied to specimens killed and dehydrated in air or dehydrated and stored in glycerol. Atomic force microscopy scanning of nematodes in constant height mode yielded replicated high-resolution images of the cuticle showing anatomical details such as annulations and lateral fields. Submicrometer scale images allowed the identification of planar regions for further higher resolution scans.     

Force field influences in beta-hairpin folding simulations

All-atom force fields are now routinely used for more detailed understanding of protein folding mechanisms. However, it has been pointed out that use of all-atom force fields does not guarantee more accurate representations of proteins; in fact, sometimes it even leads to biased structural distributions. Indeed, several issues remain to be solved in force field developments, such as accurate treatment of implicit solvation for efficient conformational sampling and proper treatment of backbone interactions for secondary structure propensities. In this study, we first investigate the quality of several recently improved backbone interaction schemes in AMBER for folding simulations of a beta-hairpin peptide, and further study their influences on the peptide's folding mechanism. Due to the significant number of simulations needed for a thorough analysis of tested force fields, the implicit Poisson-Boltzmann solvent was used in all simulations. The chosen implicit solvent was found to be reasonable for studies of secondary structures based on a set of simulations of both alpha-helical and beta-hairpin peptides with the TIP3P explicit solvent as benchmark. Replica exchange molecular dynamics was also utilized for further efficient conformational sampling. Among the tested AMBER force fields, ff03 and a revised ff99 force field were found to produce structural and thermodynamic data in comparably good agreement with the experiment. However, detailed folding pathways, such as the order of backbone hydrogen bond zipping and the existence of intermediate states, are different between the two force fields, leading to force field-dependent folding mechanisms.     

Surface Potential Measurement of Bacteria Using Kelvin Probe Force Microscopy

Surface potential is a commonly overlooked physical characteristic that plays a dominant role in the adhesion of microorganisms to substrate surfaces. Kelvin probe force microscopy (KPFM) is a module of atomic force microscopy (AFM) that measures the contact potential difference between surfaces at the nano-scale. The combination of KPFM with AFM allows for the simultaneous generation of surface potential and topographical maps of biological samples such as bacterial cells. Here, we employ KPFM to examine the effects of surface potential on microbial adhesion to medically relevant surfaces such as stainless steel and gold. Surface potential maps revealed differences in surface potential for microbial membranes on different material substrates. A step-height graph was generated to show the difference in surface potential at a boundary area between the substrate surface and microorganisms. Changes in cellular membrane surface potential have been linked with changes in cellular metabolism and motility. Therefore, KPFM represents a powerful tool that can be utilized to examine the changes of microbial membrane surface potential upon adhesion to various substrate surfaces. In this study, we demonstrate the procedure to characterize the surface potential of individual methicillin-resistant Staphylococcus aureus USA100 cells on stainless steel and gold using KPFM.     

Multifunctional Setup for Studying Human Motor Control Using Transcranial Magnetic Stimulation,Electromyography, Motion Capture,and Virtual Reality

The study of neuromuscular control of movement in humans is accomplished with numerous technologies. Non-invasive methods for investigating neuromuscular function include transcranial magnetic stimulation, electromyography, and three-dimensional motion capture. The advent of readily available and cost-effective virtual reality solutions has expanded the capabilities of researchers in recreating “real-world” environments and movements in a laboratory setting. Naturalistic movement analysis will not only garner a greater understanding of motor control in healthy individuals, but also permit the design of experiments and rehabilitation strategies that target specific motor impairments (e.g. stroke). The combined use of these tools will lead to increasingly deeper understanding of neural mechanisms of motor control. A key requirement when combining these data acquisition systems is fine temporal correspondence between the various data streams. This protocol describes a multifunctional system’s overall connectivity, intersystem signaling, and the temporal synchronization of recorded data. Synchronization of the component systems is primarily accomplished through the use of a customizable circuit, readily made with off the shelf components and minimal electronics assembly skills.     

Measuring “Unmeasurable” Folding Kinetics of Proteins by Single-Molecule Force Spectroscopy

Folding and unfolding are fundamental biological processes in cell and are important for the biological functions of proteins. Characterizing the folding and unfolding kinetics of proteins is important for understanding the energetic landscape leading to the active native conformations of these molecules. However, the thermal or chemical-induced unfolding of many proteins is irreversible in vitro, precluding characterization of the folding kinetics of such proteins, just as it is impossible to “un-boil” an egg. Irreversible unfolding often manifests as irreversible aggregation of unfolded polypeptide chains, which typically occurs between denatured protein molecules in response to the exposure of hydrophobic residues to solvent. An example of such a protein where thermal denaturation results in irreversible aggregation is the β-1,4 endoxylanase from Bacillus circulans (BCX). Here, we report the use of single-molecule atomic force microscopy to directly measure the folding kinetics of BCX in vitro. By mechanically unfolding BCX, we essentially allowed only one unfolded molecule to exist in solution at a given time, effectively eliminating the possibility for aggregation. We found that BCX can readily refold back to the native state, allowing us to measure its folding kinetics for the first time. Our results demonstrate that single-molecule force-spectroscopy-based methods can adequately tackle the challenge of “un-boiling eggs”, providing a general methodology to characterize the folding kinetics of many proteins that suffer from irreversible denaturation and thus cannot be characterized using traditional equilibrium methodologies.     

暗示性运动加工的认知神经机制

暗示性运动是指个体观看静止图片时从中知觉到的运动.研究者采用高低认知水平两类暗示性运动刺激材料,借助"冻结帧"、直接观看、运动后效和f MRI适应等任务范式,探讨了注意和意识在暗示性运动加工中的作用及其记忆特点;并借助脑成像等技术,考察了颞中区、颞上皮层区、颞上沟、镜像神经元系统等脑区在暗示性运动加工中的作用.但由于暗示性运动加工涉及"视觉腹侧通路与背侧通路功能的分离与整合"问题,目前对相关研究结果和解释还存在争议,暗示性运动加工的认知神经机制仍有待于进一步研究.     

Transthyretin fibrillogenesis entails the assembly of monomers: a molecular model for in vitro assembled transthyretin amyloid-like fibrils

Extracellular accumulation of transthyretin (TTR) variants in the form of fibrillar amyloid deposits is the pathological hallmark of familial amyloidotic polyneuropathy (FAP). The TTR Leu55Pro variant occurs in the most aggressive forms of this disease. Inhibition of TTR wild-type (WT) and particularly TTR Leu55Pro fibril formation is of interest as a potential therapeutic strategy and requires a thorough understanding of the fibril assembly mechanism. To this end, we report on the in vitro assembly properties as observed by transmission electron microscopy (TEM), atomic force microscopy (AFM) and quantitative scanning transmission electron microscopy (STEM) for both TTR WT fibrils produced by acidification, and TTR Leu55Pro fibrils assembled at physiological pH. The morphological features and dimensions of TTR WT and TTR Leu55Pro fibrils were similar, with up to 300 nm long, 8 nm wide fibrils being the most prominent species in both cases. Other species were evident; 4-5 nm wide fibrils, 9-10 nm wide fibrils and oligomers of various sizes. STEM mass-per-length (MPL) measurements revealed discrete fibril types with masses of 9.5 and 14.0(+/-1.4) KDa/nm for TTR WT fibrils and 13.7, 18.5 and 23.2(+/-1.5) kDa/nm for TTR Leu55Pro fibrils. These MPL values are consistent with a model in which fibrillar TTR structures are composed of two, three, four or five elementary protofilaments, with each protofilament being a vertical stack of structurally modified TTR monomers assembled with the 2.9 nm axial monomer-monomer spacing indicated by X-ray fibre diffraction data. Ex vivo TTR amyloid fibrils were examined. From their morphological appearance compared to these, the in vitro assembled TTR WT and Leu55Pro fibrils examined may represent immature fibrillar species. The in vitro system operating at physiological pH for TTR Leu55Pro and the model presented for the molecular arrangement of TTR monomers within fibrils may, therefore, describe early fibril assembly events in vivo.     

磁性聚乙二醇载体固定化葡萄糖淀粉酶的研究

以磁性聚乙二醇为载体,通过吸附-交联法固定化糖化酶.研究了戊二醛浓度、pH值及加酶量对酶固定化的影响.并对固定化酶的最适温度、最适pH、米氏常数、热稳定性及操作稳定性等进行了探讨.     

Single Wavelength Shadow Imaging of Caenorhabditis elegans Locomotion Including Force Estimates

This study demonstrates an inexpensive and straightforward technique that allows the measurement of physical properties such as position, velocity, acceleration and forces involved in the locomotory behavior of nematodes suspended in a column of water in response to single wavelengths of light. We demonstrate how to evaluate the locomotion of a microscopic organism using Single Wavelength Shadow Imaging (SWSI) using two different examples.The first example is a systematic and statistically viable study of the average descent of C. elegans in a column of water. For this study, we used living and dead wildtype C. elegans. When we compared the velocity and direction of nematode active movement with the passive descent of dead worms within the gravitational field, this study showed no difference in descent-times. The average descent was 1.5 mm/sec ± 0.1 mm/sec for both the live and dead worms using 633 nm coherent light.The second example is a case study of select individual C. elegans changing direction during the descent in a vertical water column. Acceleration and force are analyzed in this example. This case study demonstrates the scope of other physical properties that can be evaluated using SWSI while evaluating the behavior using single wavelengths in an environment that is not accessible with traditional microscopes. Using this analysis we estimated an individual nematode is capable of thrusting with a force in excess of 28 nN.Our findings indicate that living nematodes exert 28 nN when turning, or moving against the gravitational field. The findings further suggest that nematodes passively descend in a column of water, but can actively resist the force of gravity primarily by turning direction.     

Growth of Collagen Fibril Seeds from Embryonic Tendon: Fractured Fibril Ends Nucleate New Tip Growth

Collagen fibrils are the principal tensile element of vertebrate tissues where they occur in the extracellular matrix as spatially organised arrays. A major challenge is to understand how the mechanisms of nucleation, growth and remodelling yield fibrils of tissue-specific diameter and length. Here we have developed a seeding system whereby collagen fibrils were isolated from avian embryonic tendon and added to purified collagen solution, in order to characterise fibril surface nucleation and growth mechanisms. Fragmentation of tendon in liquid nitrogen followed by Dounce homogenisation generated fibril length fragments. Most (> 94%) of the fractured ends of fibrils, which show an abrupt square profile, were found to act as nucleation sites for further growth by molecular accretion. The mechanism of this nucleation and growth process was investigated by transmission electron microscopy, atomic force microscopy and scanning transmission electron microscopy mass mapping. Typically, a single growth spur occurred on the N-terminal end of seed fibrils whilst twin spurs frequently formed on the C-terminal end before merging into a single tip projection. The surface nucleation and growth process generated a smoothly tapered tip that achieved maximum diameter when the axial extension reached ∼ 13 μm. Lateral growth also occurred along the entire length of all seed fibrils that contained tip projections. The data support a model of collagen fibril growth in which the broken ends of fibrils are nucleation sites for propagation in opposite axial directions. The observed fibril growth behaviour has direct relevance to tendon matrix remodelling and repair processes that might involve rupture of collagen fibrils.     

What you feel is what you see: inverse dynamics estimation underlies the resistive sensation of a delayed cursor

How our central nervous system (CNS) learns and exploits relationships between force and motion is a fundamental issue in computational neuroscience. While several lines of evidence have suggested that the CNS predicts motion states and signals from motor commands for control and perception (forward dynamics), it remains controversial whether it also performs the ‘inverse’ computation, i.e. the estimation of force from motion (inverse dynamics). Here, we show that the resistive sensation we experience while moving a delayed cursor, perceived purely from the change in visual motion, provides evidence of the inverse computation. To clearly specify the computational process underlying the sensation, we systematically varied the visual feedback and examined its effect on the strength of the sensation. In contrast to the prevailing theory that sensory prediction errors modulate our perception, the sensation did not correlate with errors in cursor motion due to the delay. Instead, it correlated with the amount of exposure to the forward acceleration of the cursor. This indicates that the delayed cursor is interpreted as a mechanical load, and the sensation represents its visually implied reaction force. Namely, the CNS automatically computes inverse dynamics, using visually detected motions, to monitor the dynamic forces involved in our actions.     

一阶运动和二阶运动方向辨别的知觉学习及传递性研究

为了明确视觉系统对一阶运动和二阶运动识别机制之间的相互关系,采用一阶运动和二阶运动的正弦光栅刺激,在旁中央凹对训练组(14名被试)进行运动方向辨别的知觉学习训练．通过比较训练前后的对比敏感度变化,并同对照组(11名被试)的结果比较后发现：a．在旁中央凹,一阶运动光栅方向辨别的训练提高了被试辨别一阶运动方向的能力,但是这种提高的效果却不能传递到二阶运动光栅的方向辨别任务当中;b．二阶运动光栅方向辨别的训练在提高被试二阶运动方向识别能力的同时,也提高了被试在一阶运动光栅方向辨别任务中的表现．这一训练效果的“非对称”传递现象提示,人的视觉系统中存在两种不同的机制分别用于感知一阶运动和二阶运动,但这两种机制并非截然不同,而是部分分离的．