共查询到20条相似文献,搜索用时 15 毫秒
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Siffalovic P Michelswirth M Bartz P Decker B Agena C Schäfer C Molter S Ros R Bach M Neumann M Anselmetti D Mattay J Heinzmann U Drescher M 《Journal of biotechnology》2004,112(1-2):139-149
Self-assembled monolayer films based on iodobenzoyloxy-functionalized resorc[4]arenes were prepared on gold substrates to serve as model systems for future time-resolved studies of molecular recognition, a mechanism of outstanding importance in bioorganic systems. The film properties were tested using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and imaging ellipsometry. An apparatus for time-resolved electron spectroscopy utilizing femtosecond soft X-ray pulses is capable of detecting iodine core-level photolines and the photoinduced dissociation after ultraviolet illumination. The developed technique holds promise for tracking the temporal evolution of chemical shifts of atomic markers as local probes for the dynamics of the guest-host interaction. 相似文献
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The 1,3-regiospecifique lipase, Lipozyme IM, catalyzed the esterification of lauric acid and glycerol in a homogeneous system. To overcome the drawback of the insolubility of glycerol in hexane, which is extensively used in enzymatic synthesis, a mixture of n-hexane/tert-butanol (1:1, v/v) was used leading to a monophasic system. The conversion of lauric acid into monolaurin was 65% in 8 h, when a molar ratio of glycerol to fatty acid (5:1) was used with the fatty acid at 0.1 M, and the phenomenon of acyl migration was minimized. 相似文献
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E Próchniewicz 《Biochimica et biophysica acta》1979,579(2):346-358
Crosslinking of F-actin by a bifunctional reagent glutaraldehyde resulted in a marked decrease of viscosity and length of F-actin filaments. The extent and rate of superprecipitation of actomyosin reconstituted from the modified actin were lower than those of unmodified actin-myosin complex, but activation of heavy meromyosin ATPase by the crosslinked actin was higher than by unmodified one. Heavy meromyosin ATPase activated by the crosslinked actin was distinctly less dependent on KCl concentration than that activated by unmodified actin. Turbidity of the modified acto-heavy meromyosin in the presence of ATP exceeded the sum of turbidities of actin and heavy meromyosin, whereas in the case of unmodified acto-heavy meromyosin the turbidity was comparable to that for noninteracting system. The difference in activation of heavy meromyosin. ATPase by the cross-linked and unmodified actin, clearly seen at room temperature, significantly diminished when temperature was lowered to 0 degrees C. 相似文献
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T. R. Hennessy 《Bulletin of mathematical biology》1974,36(5-6):505-526
A mathematical model is proposed to examine the interaction between blood perfusion and gas diffusion in the uptake of inert gases in tissue. The standard Haldane perfusion model is contrasted with the Hills radial bulk diffusion model in a variety of homogeneous tissue types used in decompression theory. It is the intention of the present analysis to fix ideas on the role of diffusion, perfusion and axial concentration and quantitative studies are given and seem to show that Haldane's perfusion theory is at best a poor approximation even at asymptotic times. It is shown that a strong interaction exists between diffusion and perfusion in muscle tissue and neither approach adequately describes the actual uptake half-time of an inert gas. 相似文献
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A F Lehner T G Muldoon V B Mahesh E D Bransome L B Hendry 《Molecular endocrinology (Baltimore, Md.)》1987,1(5):377-387
Molecular modeling studies show that estrogens such as estradiol complement the topography of spaces between base pairs in unwound DNA and simultaneously hydrogen bond phosphate moieties on opposite strands. We demonstrate here that the phytoestrogen coumestrol has this capability, in addition to its documented properties of UV absorbance at lambda greater than 300 nm and fluorescence. The latter properties enable spectroscopic examination of interactions with DNA by methods not possible with estrogenic steroids. On exposure to calf thymus DNA, the UV spectrum of coumestrol displays a bathochromic shift and simultaneous hypochromic effect with an isosbestic point at 370 nm, suggesting a shift between coexisting free and bound states. Similar results are observed with the intercalating agents adriamycin, ethidium bromide, and acridine. The fluorescence spectrum of coumestrol is quenched on exposure to DNA as are those of adriamycin and acridine. Coumestrol differs from the intercalators in that denatured DNA does not affect its UV spectrum or alter its relative fluorescence yield. Unlike classical intercalators, coumestrol has no influence on the thermal stability of calf thymus DNA. Preliminary electrophoretic analysis of DNA plasmid conformers indicates that coumestrol is incapable of significantly altering DNA superhelical density, in contrast to ethidium bromide. These initial physicochemical data provide evidence for the DNA base-estrogen electronic and/or hydrophobic interactions suggested by modeling studies, yet tend to rule out classical intercalation as an explanation for these phenomena. 相似文献
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Distance dependence of the tryptophan-disulfide interaction at the triplet level from pulsed phosphorescence studies on a model system. 总被引:1,自引:1,他引:1
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In the present study the distance dependence of tryptophan-disulfide interaction is examined with a view to both utilizing the interaction as a more quantitative indicator of subtle conformational changes in proteins as well as elucidating the interaction mechanism. To examine perturbations specifically at the indole triplet level 2-(3-indolyl)-ethyl phenyl ketone (IEPK) in which excitation is transferred with high efficiency to the triplet state of the indole moiety was employed. Phosphorescence decays of IEPK excited by a laser pulse in 70/30 (vol/vol) ethanolether at 77 K were measured in the presence of various concentrations of simple disulfides. The nonexponential phosphorescence decays arising from a distribution of fixed chromophoreperturber separations and the steady-state quenching of IEPK were accounted for with an exponential dependence of the quenching rate constant with distance. The small effective Bohr radius (0.8 A) that appears in the exponent emphasizes the localized nature of the interaction. Comparison of the triplet quenching rate constant obtained at quencher contact with IEPK to that estimated in proteins suggests a dependence on the triplet energy of the indole moiety and an endothermic nature for the quenching process. The study predicts that in proteins tryptophan-disulfide interactions are very localized in nature and should give rise to detectable anomalous decays only out to 2 A beyond van der Waals contact between the interacting partners. 相似文献
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Kinetic identification of a two-state glucagon receptor system in isolated hepatocytes. Interconversion of homogeneous receptors 总被引:1,自引:0,他引:1
E M Horwitz W T Jenkins N M Hoosein R S Gurd 《The Journal of biological chemistry》1985,260(16):9307-9315
A detailed kinetic study was performed to investigate the interaction of glucagon with receptors on freshly isolated hepatocytes. Competition binding assay results fit a mathematical expression for a single site noncooperative model of binding. Glucagon was shown to bind with first-order kinetics at six-hormone concentrations (0.02-0.50 nM) at 0 and 37 degrees C. The observed pseudo-first-order rate constants are directly proportional to the hormone concentration at 0 degree C, but display a downward deviation from linearity at 37 degrees C. Dissociation of glucagon exhibited biexponential character at 37 degrees C which was not seen at 0 degree C. The biphasic dissociation at 37 degrees C was resolved into rapid (t1/2 = 1.9 min) and slow (t1/2 = 27.7 min) components. The distribution of the total bound hormone between the rapidly and slowly dissociating complexes was not dependent upon the extent of receptor occupancy. The absolute quantity of rapidly dissociating hormone-receptor complexes was constant at all times examined; however, the fraction of slowly dissociating hormone-receptor complexes was found to increase with increasing incubation time. The results indicate that a homogeneous population of hepatic receptors undergoes a time-dependent, temperature-dependent conversion from one state to another in a two-stage sequential manner. 相似文献
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Crosslinking induced by ultraviolet light irradiation at 254 nm has been utilized to investigate the structure of chromatin and isolated nucleosomes. The results presented here imply that the four core histones, as well as histone H1, have reactive groups within a bond length of the DNA bases. In nucleosomes depleted of H1, all of the core histones react similarly with the DNA and form crosslinks. In chromatin, the rate of crosslinking of all histones to DNA is essentially similar. Comparison of mononucleosomes, dinucleosomes and whole chromatin shows that the rate of crosslinking increases significantly with increasing number of connected nucleosomes. These differences in the rate of crosslinking are interpreted in terms of interactions between neighbouring nucleosomes on the chromatin fiber, which are absent in an isolated mononucleosome. 相似文献
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When intact platelets are incubated at 37 degrees C with Concanavalin A (ConA), the two major surface membrane proteins GPIIb and III become associated with the Triton-insoluble cytoskeleton. Preincubation of platelets with a variety of metabolic inhibitors, including cytochalasin B, 2-deoxy-D-glucose, and antimycin A or lidocaine, had no effect on the ability of ConA to produce this effect. These results suggested that the ConA-induced anchorage of GPIIb and III to the Triton-insoluble cytoskeleton is a passive process requiring clustering of GPIIb-III molecules but not requiring the metabolic energy of an intact cell. This was supported by experiments that showed that ConA binding to plasma membrane-rich fractions at 37 degrees C could induce association of GPIIb and III with a sedimentable actin-rich, Triton-insoluble membrane matrix. Similar results were obtained when membranes were first isolated from ConA-treated cells. Adding DNAse I, an actin depolymerizing agent, into the Triton extraction buffer inhibited the ConA-induced sedimentation of GPIIb-III and actin by 50% in the presence of Mg2+-ATP. Treatment of ConA-treated membranes with dimethyl-3,3'-dithiobispropiomidate, a bifunctional, reducible protein crosslinking agent, produced Triton-insoluble crosslinked species of discrete molecular weights. When these cross-linked species were analyzed by SDS-PAGE in the presence of beta-mercaptoethanol, they were found to be composed of a 180-200 K dalton protein, GPIIb, GPIII, and actin. Crosslinking of these components was equally effective after Triton treatment and indicated as well that the species crosslinked in the intact membrane was stable after Triton extraction. Addition of crosslinker to membranes not treated with ConA produced similar crosslinked species. Analysis of their composition on reduced gels revealed that the amounts of GPIIb and III were reduced greatly (less than 10% of the total input GPIIb and III) but that the 180-200 k dalton protein and actin content were similar to that seen with ConA-treated membranes. These results are consistent with the notion that ConA clusters mobile, unanchored molecules of GPIIb-III (approximately 90-95% of the total) around a small fraction of IIb-III that is associated with a submembranous cytoskeleton. 相似文献
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A great variety of biological groups form a self-organized swarming motion at some point during their life spans, which has two prominent collective features: common velocity and constant spacings among members. In this paper, we present a general individual-based motion framework to explain such collective motion of swarms in homogeneous environments. The motion framework utilizes the concept of social interactions that has been widely accepted throughout the literature. We assume that during the motion of the swarm, each member senses and interacts with its neighbors via virtual Attraction/Alignment/Repulsion (A/A/R) forces, while perceiving and following the gradient force of the environment. During the swarm's motion, the neighborhood and the interaction relations among members may dynamically change. To explicitly consider the effect of such dynamic change on the emergence of swarm's collective behavior, we use an algebraic graph to model the topology of the interaction and the neighborhood relations among the members.By using mathematical tools of nonsmooth analysis theory and Lyapunov stability theory, we analytically prove that if the A/A/R forces have limited ranges, and the attraction/repulsion forces are balanced at a certain range, the proposed framework leads to a parallel type of collective motion of the swarm. We mathematically show that the velocities of all swarm members asymptotically converge to a common value and the spacings among neighbors remain unchanging. In addition to the mathematical analysis, a few sets of simulation results are included to demonstrate the presented framework.The contributions of this paper are twofold: First, unlike most works in the literature that mainly use computer simulations to study the swarming phenomena, this paper provides an analytical methodology to investigate how the collective group behavior is self-organized by individual motions. Second, the presented motion framework works over a general range of A/A/R interactions. In other words, we analytically prove that the commonly used A/A/R model can lead to a collective motion of the swarm. In addition, we show that the alternative model in the literature that uses only attraction/repulsion (A/R) interactions is in fact a special case of the A/A/R model. 相似文献
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Vi Pham John D. Wade Patrick M. Sexton 《International journal of peptide research and therapeutics》2003,10(5-6):447-453
Summary Understanding the molecular mechanism underlying how the peptide ligands bind to their receptors with subsequent receptor activation and cellular response is of great long-term value in designing receptor-targeted drugs. This is more difficult for class-II G protein-coupled receptors as only minimal structural data is available and their natural peptide ligands contain a large and diffuse pharmacophore. To address this problem, photoaffinity labeling studies have been developed to identify the spatial proximity between the photophore-modified ligand and its receptor. This minireview looks at the application of this approach in determining the proximal sites between class-II G protein-coupled receptor peptide ligands and their corresponding receptors, including parathyroid hormone, secretin and vasoactive intestinal polypeptide. More specifically, we will highlight interaction sites between positions 19, 16 and 26 of calcitonin with C134−K141, and F137 and T30 of the receptor, respectively. 相似文献
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P M Steinert E Candi E Tarcsa L N Marekov M Sette M Paci B Ciani P Guerrieri G Melino 《Cell death and differentiation》1999,6(9):916-930
The cell envelope (CE) is a vital structure for barrier function in terminally differentiated dead stratified squamous epithelia. It is assembled by transglutaminase (TGase) cross-linking of several proteins, including SPR3 in certain specialized epithelia normally subjected to mechanical trauma. We have expressed recombinant human SPR3 in order to study its cross-linking properties. It serves as a complete substrate for, and is cross-linked at similar efficiencies by, the three enzymes (TGases 1, 2 and 3) that are widely expressed in many epithelia. Multiple adjacent glutamines (4, 5, 16, 17, 18, 19 and 167) and lysines (6, 21, 164, 166 and 168) of only head and tail domain sequences are used for cross-linking. However, each enzyme preferentially uses certain residues on the head domain. Moreover, our in vitro data suggest a defined temporal order of cross-linking of SPR3 in vivo: It is first cross-linked by TGase 3 into short intra- and inter-chain oligomers which are later further cross-linked to the CE by TGase 1. To investigate the absence of cross-linking in the central domain (e.g. lysine in position 2 of each of the 16 repeats) we performed structural studies on recombinant SPR3 and on a synthetic peptide containing three repeats of the central domain. 2D H-1 NMR spectroscopy, TOCSY and ROESY, shows strong and medium intensity NOEs connectivities along the amino acid sequence with one weak long range NOE contact between Thr and Cys of subsequent repeats. Distance geometry computation on the basis of intensities of NOEs found generated 50 compatible structures grouped in three main families differing by the number of H-bonds. These measurements were repeated at different concentrations of trifluoroethanol (TFE)-water mixture, an alpha-helical promoting solvent, in order to check the stability of the conformations determined; no changes were observed up to 50% TFE in solution. Also temperature changes did not produce any variation in the ROESY spectrum in the same condition as above. The NMR and circular dichroism data strongly indicate the presence of an ordered (not alpha-helix nor beta-sheet) highly flexible structure in the eight amino acids repetitive units of SPR3, confirming the prediction of one possible beta-turn per each repeating unit. Thus, biochemical and biophysical data, strongly support SPR3 to function as a flexible cross-bridging protein to provide tensile strength or rigidity to the CE of the stratified squamous epithelia in which it is expressed. 相似文献
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Pure chitosan, glutaraldehyde crosslinked chitosan, and a blend of chitosan with poly(ethylene oxide) (PEO) membranes were prepared. The three membranes were characterized in terms of their swelling capacities as well as their permeabilities to a drug model (sulfamerazine sodium salt). For the permeation experiments, the variables analyzed were the type of membrane and the initial drug concentration in the liquid phase (from 0.1% to 1.5%). Permeability coefficients were calculated using UV spectroscopy. The results showed that for the three analyzed membranes, the permeability did not change with time (over the studied time interval). An increase in the permeability for CHI/PEO membranes compared to those made of pure chitosan was also observed, possibly due to microporous region formation and/or crystallinity reduction. For the crosslinked membrane, an even higher increase in the permeability coefficient was observed. In this case, the increase was attributed to free volume variation. 相似文献
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Crosslinking of DNA fibers by histone H1 or phosphorylated on Ser-37 histone H1, and by the individual fragments of the H1 polypeptide chain was studied by the method of turbidimetry. The dependence of the turbidity of DNA-protein complexes on the ionic strength in solution suggests that the condensation of H1.DNA complexes in vitro is apparently due to both specific histone-DNA interactions with the contribution of hydrogen and/or hydrophobic bonds and the formation of polycationic "bridges" fastening the DNA fibers. The effectiveness of the condensation is postulated to be a function of a proportion between the two mechanisms which in turn can be controlled by slight changes in ionic surroundings. The sharp dependence of shrinkage of H1.DNA complexes on ionic strength at "physiological" salt concentrations could provide a mechanism to regulate density and consequently the total activity of chromatin in the cell nuclei. The phosphorylation of histone H1 on Ser-37 by a specific histone kinase does not noticeably affect the pattern of DNA crosslinking by the H1. 相似文献