猪十二指肠组织灌流培养与静态培养比较

组织灌流培养和静态培养是肠道组织体外培养最常见的两种方法,但目前尚不清楚这两种培养方法哪种更适合用于体外胃肠激素分泌的研究.以猪十二指肠组织为研究对象,首先比较L-精氨酸下两种体外培养方法对组织胆囊收缩素(Cholecystokinin,CCK)分泌和组织活性乳酸脱氢酶(Lactate dehydrogenase,LD...     

Preparation of DNA-crosslinked Polyacrylamide Hydrogels

Mechanobiology is an emerging scientific area that addresses the critical role of physical cues in directing cell morphology and function. For example, the effect of tissue elasticity on cell function is a major area of mechanobiology research because tissue stiffness modulates with disease, development, and injury. Static tissue-mimicking materials, or materials that cannot alter stiffness once cells are plated, are predominately used to investigate the effects of tissue stiffness on cell functions. While information gathered from static studies is valuable, these studies are not indicative of the dynamic nature of the cellular microenvironment in vivo. To better address the effects of dynamic stiffness on cell function, we developed a DNA-crosslinked polyacrylamide hydrogel system (DNA gels). Unlike other dynamic substrates, DNA gels have the ability to decrease or increase in stiffness after fabrication without stimuli. DNA gels consist of DNA crosslinks that are polymerized into a polyacrylamide backbone. Adding and removing crosslinks via delivery of single-stranded DNA allows temporal, spatial, and reversible control of gel elasticity. We have shown in previous reports that dynamic modulation of DNA gel elasticity influences fibroblast and neuron behavior. In this report and video, we provide a schematic that describes the DNA gel crosslinking mechanisms and step-by-step instructions on the preparation DNA gels.     

稳恒磁场对两种不同构象状态的离体牛肝过氧化氢酶的生物学效应研究

通过活力测定,紫外差光谱,多维荧光光谱及差示扫描量热分析,研究了0.23～0.61T稳恒磁场对两种不同构象状态的离体牛肝过氧化氢酶的生物学效应,被选择用于研究的酶的构象状态分别为4℃的钝化状态和25℃的活化状态,二者具有明显不同的构象,4℃时,酚分子处于钝化状态,经0.23～0.61T稳恒磁场处理不同的时间后,几乎不表现出任何磁生物学效应;25℃时,酶分子处于活化状态,经磁场处理后,表现出明显的磁生物学效应;酶活力增加,同时构象发生变化。构象变化导致λ210～310nm紫外差光谱的出现,荧光偏振度的增加,在λ330nm荧光发射峰发射强度的改变及差示扫描量热曲线的产生,研究结果表明：不同的初始构象状态可能是产生不同磁效应的根本原因。     

甘肃省民勤连古城自然保护区沙木蓼种群的结构与动态

根据甘肃省民勤连古城自然保护区沙木蓼种群的生境和植被差异,分别选择低山剥蚀残丘覆沙地(生境Ⅰ)和山前倾斜洪积扇沙地,有小型风积沙丘(生境Ⅱ)和无风积沙丘(生境Ⅲ)3种生境类型样地,对其种群的发育状况、年龄结构、静态生命曲线与分布格局进行了研究,揭示沙木蓼种群动态规律并评价其在构建荒漠植被方面的价值,为科学合理地管护和持续利用沙木蓼种质资源提供科学依据。研究结果表明,1)沙木蓼苗龄级、幼龄级、成熟龄级和老龄级种群密度大小顺序为生境Ⅲ生境Ⅰ生境Ⅱ,而3种生境中同龄级种群在株高、冠幅、新梢生长量方面差异不显著;2)苗龄级种群在3种生境下都占据了较大的优势地位,对沙木蓼种群的更新具有积极作用。生境Ⅰ和Ⅲ的幼龄级和成熟龄级的年龄结构为连续增长型,老龄级为独立的增长型,种群具有较大的发展空间。而生境Ⅱ的幼龄级和成熟龄级种群的年龄结构为连续的稳定型,老龄级种群为稳定型,种群结构比较稳定。3)种群lx,dx和qx曲线在苗龄级、幼龄级和成熟龄级阶段具有相同的变化趋势,其中苗龄级种群向幼龄级种群转变过程中均呈下降趋势,幼龄级和成熟级种群发育过程中基本保持平稳,但在老龄级种群阶段3种曲线变化趋势的差异性较大,其中生境Ⅰ和Ⅲ种群产生重叠,沙木蓼种群的死亡高峰主要发生在苗龄级和老龄级阶段,具有前期增长,中期稳定,后期衰退的一般规律。4)沙木蓼苗龄级、幼龄级和成熟级种群的分布格局均为聚集分布,而老龄级种群为随机分布。以上分析表明,3种生境下沙木蓼种群更新能力旺盛,种群结构趋于合理,生境差异(风沙流活动)只对土壤种子库、种子萌发和幼苗保存具有显著影响,对其它龄级种群发育没有显著影响,在荒漠植被演变中表现出较强的适应能力和优越性,因此沙木蓼在荒漠植被恢复和重建中具有重要的利用价值。     

Respirometry increases cortisol levels in rainbow trout Oncorhynchus mykiss: implications for measurements of metabolic rate

This study aimed to assess the extent to which chasing, handling and confining Oncorhynchus mykiss to a small respirometer chamber during respirometric experiments is stressful and affects metabolic measurements. The study observed increased cortisol levels in animals tested using a chase protocol and subsequent intermittent‐flow respirometry, suggesting that this procedural treatment may stress animals.     

Integrated biophysical studies implicate partial unfolding of NBD1 of CFTR in the molecular pathogenesis of F508del cystic fibrosis

The lethal genetic disease cystic fibrosis is caused predominantly by in‐frame deletion of phenylalanine 508 in the cystic fibrosis transmembrane conductance regulator (CFTR). F508 is located in the first nucleotide‐binding domain (NBD1) of CFTR, which functions as an ATP‐gated chloride channel on the cell surface. The F508del mutation blocks CFTR export to the surface due to aberrant retention in the endoplasmic reticulum. While it was assumed that F508del interferes with NBD1 folding, biophysical studies of purified NBD1 have given conflicting results concerning the mutation's influence on domain folding and stability. We have conducted isothermal (this paper) and thermal (accompanying paper) denaturation studies of human NBD1 using a variety of biophysical techniques, including simultaneous circular dichroism, intrinsic fluorescence, and static light‐scattering measurements. These studies show that, in the absence of ATP, NBD1 unfolds via two sequential conformational transitions. The first, which is strongly influenced by F508del, involves partial unfolding and leads to aggregation accompanied by an increase in tryptophan fluorescence. The second, which is not significantly influenced by F508del, involves full unfolding of NBD1. Mg‐ATP binding delays the first transition, thereby offsetting the effect of F508del on domain stability. Evidence suggests that the initial partial unfolding transition is partially responsible for the poor in vitro solubility of human NBD1. Second‐site mutations that increase the solubility of isolated F508del‐NBD1 in vitro and suppress the trafficking defect of intact F508del‐CFTR in vivo also stabilize the protein against this transition, supporting the hypothesize that it is responsible for the pathological trafficking of F508del‐CFTR.     

Protein dynamics viewed by hydrogen exchange

To examine the relationship between protein structural dynamics and measurable hydrogen exchange (HX) data, the detailed exchange behavior of most of the backbone amide hydrogens of Staphylococcal nuclease was compared with that of their neighbors, with their structural environment, and with other information. Results show that H-bonded hydrogens are protected from exchange, with HX rate effectively zero, even when they are directly adjacent to solvent. The transition to exchange competence requires a dynamic structural excursion that removes H-bond protection and allows exposure to solvent HX catalyst. The detailed data often make clear the nature of the dynamic excursion required. These range from whole molecule unfolding, through smaller cooperative unfolding reactions of secondary structural elements, and down to local fluctuations that involve as little as a single peptide group or side chain or water molecule. The particular motion that dominates the exchange of any hydrogen is the one that allows the fastest HX rate. The motion and the rate it produces are determined by surrounding structure and not by nearness to solvent or the strength of the protecting H-bond itself or its acceptor type (main chain, side chain, structurally bound water). Many of these motions occur over time scales that are appropriate for biochemical function.     

Numerical assessment of induced ELF currents in the human head due to the battery current of a digital mobile phone

In this study, the extremely low frequency (ELF) fields induced in the human head by the battery currents of a mobile phone are considered. The magnetic field induced by the phone was measured, and this data was used to calculate the resulting currents induced in the human head and brain. Both the finite element method (FEM) and finite integration technique (FIT) were used for numerical computations. The computed current density values were then compared with the guidelines given by the International Commission on Non-Ionising Radiation Protection (ICNIRP). The comparison showed that the computed exposure is well within the limits of those guidelines.     

Structural analysis of mammalian protein phosphorylation at a proteome level

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