荧光能量转移和偏振研究小牛胸腺DNA与组蛋白在高低离子盐溶液中的离合

本文研究小牛胸腺DNA和组蛋白在体外低、高离子强度盐溶液中的动态缔合与解离。 实验结果是低离子溶液中荧光给体DANsyl-Cl-组蛋白在发射峰位上荧光强度降低,荧光受体吖啶橙-DNA在发射峰位上的荧光强度增高。此两峰位上荧光受体的荧光增量比值是2.7/1(大于1),有能量转移发生,DNA和组蛋白缔合。高离子溶液中两峰位上受体的荧光增量比值降到1.6/1,能量转移减少,DNA和组蛋白解离。 低离子溶液中所得的吖啶橙-DNA的荧光偏振度P值小而高离子溶液中的P值大。说明解离的DNA硷基排列比缔合的DNA硷基排列有序程度强,进一步证明低离子溶液中DNA和组蛋白是缔合的,而高离子溶液中它们是解离的。     

Evidence from X-ray absorption fine structure spectroscopy for significant differences in the structure of concanavalin A in solution and in the crystal

We have used X-ray absorption fine structure spectroscopy (XAFS) to study and compare the structure of concanavalin A in crystals and in aqueous solution. Significant differences were found between crystal and solution in the configuration of the transition-metal site of the protein. The metal has six ligands in solution but only five in the crystal. The ligand bond lengths are shorter in the crystal than in solution. The vibrational disorder in the crystal and possibly the corresponding bond length show a negative temperature dependence whereas in solution they vary normally with temperature. The anomalous temperature dependence in the crystal suggests that as the temperature decreases the protein molecules are subject to additional stresses, which are transmitted as a tensile stress at the metal site leading to distorted geometry and lengthening and weakening of metal-ligand bonds.     

Comparison of analytically and numerically derived hydrogen exchange-rate distribution functions

Hydrogen exchange-rate probability density functions for lysozyme have been derived by numerical Laplace inversion with the computer program CONTIN. The resulting solution set includes a smooth bimodal solution in agreement with previous analytical results together with a smooth three-peak solution. Numerical analysis of lysozyme hydrogen-exchange data in glycerol/water cosolvent mixtures confirms the previous assignment of the slow-exchange peak to an exchange mechanism involving reversible unfolding. Physicochemical constrations that can reduce the size of the solution set are described. The results are compared with those obtained from previous analytical methods and the limitations of the discrete class and analytical appraches are discussed.     

Direct Staining of Reticular Fibers with Gold Chloride

Reticular fibers are selectively stained in paraffin sections of formalin-fixed or Bouin's-fixed tissue as follows: 1% aqueous solution of gold chloride for 20 min, followed by a 10 min immersion in an aqueous solution containing 5% Na₂CO₃ and 0.5% KOH. The sections then are placed in a 5% aqueous solution of KI for 2 min. Counterstaining with a 0.25% aqueous solution of methylene blue chloride is optional. The reticular fibers stain dark pink; the collagen bundles are a light pink to straw color without the counterstain, or a light blue color when the methylene blue is used.     

Temperature-jump studies and polarized absorption spectroscopy of methemoglobin-thiocyanate single crystals.

Association equilibria and association kinetics of the thiocyanate binding reaction to methemoglobin in single crystals and solution are studied using temperature-jump technique and polarized absorption spectroscopy. Different kinetic constants are found for the reaction in solution and crystal phase for the alpha- and beta-subunits of the methemoglobin tetramer. The reduction of the reactivity of the alpha- and beta-subunits in crystalline phase is 6-fold and 2.4-fold, respectively, compared to the values found in solution. The intramolecular binding reaction of the N epsilon of the distal histidine E7 which is observed in methemoglobin in solution cannot be detected in single crystals. Our results suggest that crystallization of hemoglobin has little influence on small-scale structural fluctuations which are necessary for ligands to get to the binding sites and large-scale structural motions are suppressed.     

Solid-phase synthesis and conformational properties of angiotensin converting enzyme catalytic-site peptides: the basis for a structural study on the enzyme-substrate interaction

The solution NMR conformational properties of two angiotensin converting enzyme (ACE) Zn catalytic-site 36-residue peptides, with the general sequence HEMGHX23EAIGDX3, synthesized through solid-phase 9-fluorenylmethoxycarbonyl (Fmoc) chemistry, is reported. The 1H resonance assignment of Zn-bound peptides is presented and the characteristic features of the NMR solution models of the two ACE Zn(II)-bound peptides are reported. The solid-state and solution structures of the ACE C-domain catalytic site are compared while biologically important structural similarities and differences of the N- and C-terminal catalytic sites are discussed. Additionally, the structural features of the ACE substrate, the angiotensin I (AI) decapeptide, are studied using NMR spectroscopy, in order to set the structural basis for the ACE-substrate interaction in solution.     

Raman spectra of imino acids and poly-L-hydroxyproline

The Raman spectra of poly-L -hydroxyproline in the solid state and aqueous solution have been obtained. From the spectra, the conformations of the polypeptide in the solid and aqueous solution are found to be the same. Major differences in the spectra between the solid and solution are traced to environmental influences of the pyrrolidine group as indicated by studies of the monomers. The Raman spectra of the imino acids, proline and hydroxyproline, as the dipolar ions, the hydrochlorides, and the sodium salts are also reported.     

Stability analysis for a peri-implant osseointegration model

We investigate stability of the solution of a set of partial differential equations, which is used to model a peri-implant osseointegration process. For certain parameter values, the solution has a ‘wave-like’ profile, which appears in the distribution of osteogenic cells, osteoblasts, growth factor and bone matrix. This ‘wave-like’ profile contradicts experimental observations. In our study we investigate the conditions, under which such profile appears in the solution. Those conditions are determined in terms of model parameters, by means of linear stability analysis, carried out at one of the constant solutions of the simplified system. The stability analysis was carried out for the reduced system of PDE’s, of which we prove, that it is equivalent to the original system of equations, with respect to the stability properties of constant solutions. The conclusions, derived from the linear stability analysis, are extended for the case of large perturbations. If the constant solution is unstable, then the solution of the system never converges to this constant solution. The analytical results are validated with finite element simulations. The simulations show, that stability of the constant solution could determine the behavior of the solution of the whole system, if certain initial conditions are considered.     

Contraction and Action Potentials of Frog Heart Muscles Soaked in Sucrose Solution

Isolated auricles or ventricles from the frog continue to contract, either spontaneously or when stimulated, for from 2 to 4 hours after they are placed in isotonic sucrose solution. After the muscles stop contracting in sucrose solution, contractility is partially restored when the muscles are placed in chloride Ringer's. However, contractility is usually not restored if the muscles are placed in sulfate Ringer's. Ventricles soaked in sucrose solution at 4–7°C continue to contract for 12 to 24 hours and during the first few hours in sucrose solution the contractions often are enhanced. Several types of experiment indicate that the sucrose solution does replace the Ringer's in the extracellular space. Auricles and ventricles also continue to conduct action potentials, with an overshoot, for from 30 to 360 minutes after being placed in sucrose solution. Muscles soaked in sucrose until they are inexcitable rapidly recover in chloride Ringer's but often fail to recover in sulfate Ringer's. The results are discussed in relation to theories about the generation of the action potential in cardiac muscle, and the role of the extracellular fluid in contraction.     

河蚌培养组织的几种生化成分分析

本文分析测定了三角帆蚌，褶纹冠蚌和背角无齿蚌外套膜培养组织及其培养液中的氨基酸，牛磺酸及钙含量。在珍蛛中含量较高的丙的氨酸和甘氨酸分别增加５４１％和９１％。三种蚌在培养中牛磺酸含量增加５．７８％到３倍，培养组织的钙含量增加１倍左右。同时测定了培养组织的碱性磷酸酶活性，培养组织与河蚌外套膜具有相近的比活及相对酶活。结果表明，河蚌外套膜在离体培养条件下，也具有分泌珍珠质的能力。     

On the dependence of molecular conformation on the type of solvent environment: a molecular dynamics study of cyclosporin A

The dependence of the conformation of cyclosporin A (CPA), a cyclic undecapeptide with potent immunosuppressive activity, on the type of solvent environment is examined using the computer simulation method of molecular dynamics (MD). Conformational and dynamic properties of CPA in aqueous solution are obtained from MD simulations of a CPA molecule dissolved in a box with water molecules. Corresponding properties of CPA in apolar solution are obtained from MD simulations of CPA in a box with carbontetrachloride. The results of these simulations in H2O and in CCl4 are compared to each other and to those of previous simulations of crystalline CPA and of an isolated CPA molecule. The conformation of the backbone of the cyclic polypeptide is basically independent of the type of solvent. In aqueous solution the beta-pleated sheet is slightly weaker and the gamma-turn is a bit less pronounced than in apolar solution. Side chains may adopt different conformations in different solvents. In apolar solution the hydrophobic side chain of the MeBmt residue is in an extended conformation with its hydroxyl group hydrogen bonded to the backbone carbonyl group. In aqueous solution this hydrophobic side chain folds over the core of the molecule and the mentioned hydrogen bond is broken in favor of hydrogen bonding to water molecules. The conformation obtained from the MD simulation in CCl4 nicely agrees with experimental atom-atom distance data as obtained from nmr experiments in chloroform. In aqueous solution the relaxation of atomic motion tends to be slower than in apolar solution.     

Structural study of the interaction of vanadate with the ligand 1,2-dimethyl-3-hydroxy-4-pyridinone (Hdmpp) in aqueous solution

The interaction of vanadate with the ligand 1,2-dimethyl-3-hydroxy-4-pyridinone (Hdmpp) was studied in aqueous solution using a combination of multinuclear NMR and EPR spectroscopies, as well as potentiometry and cyclic voltammetry. The different species in solution were identified and characterized, and their pKa values and stability constants determined. The vanadium complexes formed in solution are strongly dependent on media composition (ionic strength, presence of buffer), pH and metal-to-ligand ratio (M:L). Two major species--V(V)/dmpp and V(V)/(dmpp)2--are formed in a 140 mM NaCl solution within the pH range 4.5 to 9.0, when M:L = 1:2. In the presence of excess ligand (M:L < or = 1:5), only the 1:2 complex is present, and at pH < 4 paramagnetic species are detected by EPR in solution, thus indicating a reducing capacity of the ligand. Cyclic voltammetry shows that redox processes in solution are not just electron transfer, but are accompanied by chemical reactions. The pK, values and stability constants were determined both by 51V NMR spectroscopy and potentiometry. The present results have a particular interest in the understanding of the aqueous solution chemistry in aerobic conditions of bis(1,2-dimethyl-3-hydroxy-4-pyridinonato) oxovanadium(IV) complex, VO(dmpp)2, a vanadium compound with potential insulin-mimetic properties.     

一类带时滞竞争模型的周期解

研究了来源于水生种群植化相克的模型,提出了带时滞的半线性抛物系统．用上下解方法讨论了抛物方程组周期解存在性的原理,利用特征函数构造所提出抛物系统的上解,给出了正周期解存在的充分条件．     

中华蟾蜍蝌蚪对高渗溶液的耐受性

为了解中华蟾蜍蝌蚪对高渗溶液的耐受性,采用常规静态实验,用蔗糖调节溶液渗透压对蟾蜍蝌蚪进行渗透耐受实验;采用方差分析统计溶液渗透压对蟾蜍蝌蚪的存活率、体积变化和活动性的影响。结果显示,蟾蜍蝌蚪能够忍受溶液渗透压在一定范围内的变化,对渗透压较低的溶液其适应对策为调节,而对渗透压较高的溶液则为协变。蝌蚪对水溶液的耐受渗透压为1485．24mOsm,其存活率随渗透压增高而降低;同一渗透压下,蝌蚪存活率随在溶液中暴露时间的延长而降低。蟾蜍蝌蚪体内水分在不同浓度溶液中丧失的程度存在显著差异,即使在同一浓度的溶液中,体积会随时间的增加而不断缩小,并且溶液浓度越高,体积减小的速率越大。身体失水对蝌蚪的行为性会产生一定的影响,蝌蚪的活泼性随时间的延长而降低。     

Demonstration of three protonated forms of poly(A): potentiometric and conductometric study of isoionic solutions

It is shown that there are three parts on the potentiometric titration curves of isoionic solutions of poly(A) ascribed to the three protonated structures. Double-helical protonated structures are especially stable in isoionic solution. These parts on potentiometric curves are attributed to the single-stranded poly(A), to the completely protonated double-stranded poly(A+).poly(A+), and to the semiprotonated poly(A+).poly(A) structures: D, A, B forms of poly(A), respectively. pK0 values of these forms are calculated. The D form portion is found to be about 18% in isoionic solution, 40% in KCl solution (from 0.01 to 1.0 M), 40% in solution, containing 1.2 X 10(-3) M MgCl2 and 70% in 8 X 10(-4) M MgCl2 solution. The increase of MgCl2 concentration up to 8 X 10(-4) M leads to complete degradation of the double-helical structure. Only single-stranded D form exists in 5 X 10(-3) M MgCl2 solution. About 5-7% of all protons become inaccessible for titration in all solutions containing KCl and in the presence of small amounts of MgCl2. This phenomenon can not be explained by aggregation of poly(A), because all protons become accessible for titration in more concentrated MgCl2 solution when aggregation of poly(A) is significant and accompanied by the precipitation of sediment insoluble in NaOH. The supposition is made, that unprotonated double-stranded poly(A) can exist in salt-free solution at neutral pH. It is this form that is protonated with decrease of pH.     

Application of the osmotic virial equation in cryobiology

The multisolute osmotic virial equation is the only multisolute thermodynamic solution theory that has been derived from first principles and can make predictions of multisolute solution behaviour in the absence of multisolute solution data. Other solution theories either (i) include simplifying assumptions that do not take into account the interactions between different types of solute molecules or (ii) require fitting to multisolute data to obtain empirical parameters. The osmotic virial coefficients, which are obtained from single-solute data, can be used to make predictions of multisolute solution osmolality. The osmotic virial coefficients for a range of solutes of interest in cryobiology are provided in this paper, for use with concentration units of both molality and mole fraction, along with an explanation of the background and theory necessary to implement the multisolute osmotic virial equation.     

The effects of two physiological salines, Locke's and van Harreveld's, on the midgut red chromatophores of the freshwater shrimp, Caridina denticulata

It was reported previously that the red chromatophores on the midgut of a freshwater shrimp, Caridina denticulata, are affected by Locke's and van Harreveld's solutions differently, i.e., the pigment disperses in Locke's solution and concentrates with the addition of crude eyestalk extract, but in Harreveld's solution the chromatophores do not change in the saline alone nor do they respond to eyestalk extract. The differences were probably due to the osmotic pressure and Mg ion concentrations of the two solutions not being the same. Harreveld's solution is commonly used as a physiological saline for freshwater crustaceans such as crayfish. Consequently, this solution was employed at first in a previous study (Miyawaki and Tsuruda, 1985). But this solution completely inhibited pigment migration in the chromatophores. But when Locke's solution was subsequently tried, migration of the pigment in the midgut chromatophores occurred. It seemed worthwhile to examine further the effects of both solutions on these chromatophores. The results of this study are presented below.     

An exact analysis for a solute transport,due to simultaneous dialysis and ultrafiltration,in a hollow-fibre artificial kidney

Transport of a uremic solute effected by a combined dialysis and ultrafiltration procedure in a hollow-fibre artificial kidney, is investigated theoretically under standard assumptions. An exact analytical solution for the concentration profile in a blood channel is obtained by using the method of separation of variables. The necessary requirement that the solution must tend to that of pure dialysis, in the limit ultrafiltration tending to zero, is fulfilled. Exact analytical expressions are derived for the eigenconstants of the solution. In using the solution, the solute clearance is emphasized. Diffusive and ultrafiltration components of the solute clearance are defined and studied. The combined procedure is examined for middle versus small molecules and for polyacrylonitrile versus cuprophan hollow-fibres.     

A Trichrome Stain for Insect Material

Deparaffinized insect sections are brought down to water and overstained in a 0.1% solution of azocarmine G in 1% acetic acid. They are then destained in a saturated solution of orange G until the azocarmine G is removed from the endocuticle and the latter is colored pale yellow. After washing, the sections are transferred to a 5.0 % solution of phosphotungstic acid in water for 3 min. They are then rinsed in distilled water and stained in a 0.1% solution of methyl green in 1% acetic acid until the endocuticle is green. Differentiation is done in 2 changes of 95% alcohol. The sections are then dehydrated either in absolute alcohol or dioxane, cleared in a mixture of “camsal”, eucalyptol, dioxane, and paraldehyde (1:2:2:1), and mounted in Mohr and Wehrle's medium, a mountant of the Euparal type.     

Evidence for Water-Tuned Structural Differences in Proteins: An Approach Emphasizing Variations in Local Hydrophilicity

We present experimental evidence for the significant effect that water can have on the functional structure of proteins in solution. Human (HSA) and Bovine Serum Albumin (BSA) have an amino acid sequence identity of 75.52% and are chosen as model proteins. We employ EPR-based nanoscale distance measurements using double electron-electron resonance (DEER) spectroscopy and both albumins loaded with long chain fatty acids (FAs) in solution to globally (yet indirectly) characterize the tertiary protein structures from the bound ligands’ points of view. The complete primary structures and crystal structures of HSA and as of recently also BSA are available. We complement the picture as we have recently determined the DEER-derived solution structure of HSA and here present the corresponding BSA solution structure. The characteristic asymmetric FA distribution in the crystal structure of HSA can surprisingly be observed by DEER in BSA in solution. This indicates that the BSA conformational ensemble in solution seems to be narrow and close to the crystal structure of HSA. In contrast, for HSA in solution a much more symmetric FA distribution was found. Thus, conformational adaptability and flexibility dominate in the HSA solution structure while BSA seems to lack these properties. We further show that differences in amino acid hydropathies of specific structural regions in both proteins can be used to correlate the observed difference in the global (tertiary) solution structures with the differences on the primary structure level.