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  • Polymer and Materials Science  (5)
  • dynein  (2)
  • Biochemistry and Biotechnology  (1)
  • Wiley-Blackwell  (8)
  • American Society of Hematology
  • Institute of Physics
  • Springer Nature
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  • Wiley-Blackwell  (8)
  • American Society of Hematology
  • Institute of Physics
  • Springer Nature
  • 1
    ISSN: 0886-1544
    Keywords: nickel ; cadmium ; dynein ; motility ; flagella ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Bovine sperm, extracted with 0.1% Triton X-100, frozen at -20°C for 48-120 hours, and thawed, disintegrated by microtubule sliding when 1 mM MgATP was added. Microtubules and outer dense fibers (ODFs) were usually extruded in groups or “bundles.” A total of 44.5% of the cells extruded two distinct bundles, one from each side of the connecting piece, exhibiting opposite curvatures. Only one bundle was observed in 46.2% of the cells, and 9.2% showed no signs of sliding. Transmission electron microscopy (T.E.M.) showed one group consisting of the 4,5-6,7 elements, with the 9,1,2 elements on the other side of the axoneme making up the other bundle. T.E.M. revealed that when only one side of the axoneme had extruded elements, they were always from the 4,5-6,7 group. The remainder of the axoneme (8,9,1,2,3 and the central pair) was left relatively intact, suggesting a difference in the sliding response of the nine pairs of axonemal microtubules. These results indicate a predisposition for sliding between elements 7 and 8 over that between doublets 2 and 3, perhaps due to a disparity in activation thresholds. Also, both Ni2+ and Cd2+ appear to selectively block activation of 2-3 interdoublet sliding.Incubation with 0.25 mM Ni2+ prior to adding MgATP modified the percentages of sliding patterns: 8.6% demonstrated two-sided extrusion, 58.2% showed one-sided, and 33.2% had no extruded bundles. Again, when half the axoneme was missing, it was always the 4,5-6,7 group. Ten micromolar Cd2+ altered the sliding pattern similarly to Ni2+, with 28% two-sided extrusion, 55.9% one-sided extrusion and 16.1% with no extruded bundles.Either pretreatment regimen impeded extrusion of the 9,1,2 group in a high percentage of cells, compared to untreated cells. This specific inhibition of the 9,1,2 side by Ni2+ or Cd2+ is especially significant since Ni2+ also inhibits spontaneous wave initiation in bull sperm (Lindemann et al.: Journal of Cell Biology 87:420-426, 1980), and both Ni2+ and Cd2+ reportedly block the flagellar Ca2+-response in rat sperm (Lindemann and Goltz: Cell Motility and the Cytoskeleton 10:420-431, 1988; Lindemann et al.: Cell Motility and the Cytoskeleton 20:316-324, 1991). © 1993 Wiley-Liss, Inc.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 30 (1995), S. 8-16 
    ISSN: 0886-1544
    Keywords: microtubule sliding ; dynein ; sperm motility ; calcium ; vanadate ; Triton X-100 ; sperm models ; micromanipulation ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Bull sperm extracted with 0.1% Triton X-100 can be reactivated to full motility with 0.33 mM Mg-ATP (sperm models). When motile sperm models are treated with 0.66 mM NiSO4, spontaneous motility is lost. During the transition to motility arrest, the beat becomes progressively more asymmetric, finally arresting at one extreme of the beat cycle. After spontaneous motility has been lost, the flagellum retains the ability to respond to mechanical stimulation. If a microprobe is used to bend the flagellum in the direction opposite to its own prevailing curvature and released, the recoil is rapid and overshoots the equilibrium position. When the same flagellum is manipulated in the opposite direction (into a tighter bend of the existing curve), the recoil is slower and does not exceed the initial bend. If a microprobe is used to carefully bend the whole flagellum into a curve, the flagellum will resume continuous beating, but only if the imposed bend is in the direction opposite the natural curvature. The reinstated beating activity (mechanical reactivation) is sustained as long as the flagellum is held by the microprobe. The rate of change of the shear angle in these mechanically reactivated, Ni2+ -inhibited sperm suggests an impaired rate of sliding on one side of the axoneme compared to similarly restrained control sperm. It appears that Ni2+ has a selective inhibitory effect on the dynein arms that bend the flagellum in one direction. Furthermore, the remaining functional arms activate only when the flagellum is bent in the direction opposing their own action. © 1995 Wiley-Liss, Inc.
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  • 3
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 4
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nature of hydrogen bonds formed between carboxylic acid residues and histidine residues in proteins is studied by ir spectroscopy. Poly(glutamic acid) [(Glu)n] is investigated with various monomer N bases. The position of the proton transfer equilibrium OH…N ⇌ O-…H+N is determined considering the bands of the carboxylic group.It is shown that largely symmetrical double minimum energy surfaces are present in the OH…N ⇌ O-…H+N bonds when the pKa of the protonated N base is two values larger than that of the carboxylic groups of (Glu)n. Hence OH…N ⇌ O-…H+N bonds between glutamic and aspartic acid residues and histidine residues in proteins may be easily polarizable proton transfer hydrogen bonds. The polarizability of these bonds is one to two orders of magnitude larger than usual electron polarizabilities; therefore, these bonds strongly interact with their environment.It is demonstrated that water molecules shift these proton transfer equilibria in favor of the polar proton boundary structure. The access of water molecules to such bonds in proteins and therefore the position of this proton transfer equilibrium is dependent on conformation.The amide bands show that (Glu)n is α-helical with all systems. The only exception is the (Glu)n-n-propylamine system. When this system is hydrated (Glu)n is α-helical, too. When it is dried, however, (Glu)n forms antiparallel β-structure. This conformational transition, dependent on degree of hydration, is reversible. An excess of n-propylamine has the same effect on conformation as hydration.
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  • 5
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polyhistidine-carboxylic acid systems are studied by ir spectroscopy. It is shown that OH⃛N ⇌ O-…H+N bonds formed between carboxylic groups and histidine residues are easily polarizable proton-transfer hydrogen bonds when the pKa of the protonated histidine residues is about 2.8 units larger than that of the carboxylic groups. From these results it bis concluded that OH⃛N ⇌ O-⃛H+N bonds between glutamic or aspartic acid histidine residues in proteins may be easily polarizable proton-transfer bonds. Furthermore, it is demonstrated that water molecules shift the proton-transfer equilibria in these hydrogen bonds in favor of the polar structure, i.e., due to water or polar environments OH⃛N ⇌ O- ⃛H+N bonds with smaller ΔpKa values become easily polarizable proton-transfer hydrogen bonds. A consideration of the amide bands of polyhistidine shows that it can be present in five different conformations. It is shown that these conformational changes are strongly related to the degree of proton transfer. Hence, the degree of proton transfer, the degree of hydration, and conformation are not independent of each other, but are strongly coupled. Further proof for the interdependence of proton transfer and conformational changes are hysteresis effects, which are observed with studies of polyhistidine dependent on carboxylic acid, adsorption and desorption. OH⃛N ⇌ O-⃛H+N bonds between aspartic and glutamic acid and histidine residues are present in hemoglobin, in ribonucleases, and in proteases, whereby this type of bond is preferentially found in the active centers of these enzymes. It is pointed out that hydrogen bonds with such interaction properties should be of great significance for structure and especially functions of proteins in which they are present.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 50 (1996), S. 217-221 
    ISSN: 0006-3592
    Keywords: Qβ phage ; molecular evolution ; phage display ; continuous culture ; cellstat ; wall growth ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Lytic coliphage Qβ was grown in continuously cultured host bacteria using a cascade of stirred flow reactors. The apparatus was constructed so that the steady stream of exponentially growing bacterial cells passing through the stirred flow reactors served to prevent coevolution brought about by host-parasite interactions. Wall growth was the primary cause for deviation from ideal continuous culture conditions and is largely dependent on the surface structure of the host bacteria. Using an Escherichia coli strain deficient in adhesive type I pili expression, the desynchronization of single burst events could easily be followed over the course of four infection latency periods. Computer simulations based on a two-stage model for the Qβ infection cycle were in perfect agreement with the experimental data. Applications of the optimized system to strategies of molecular evolution are discussed. © 1996 John Wiley & Sons, Inc.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 15 (1971), S. 445-453 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An investigation of the behavior of poly(methyl methacrylate co ethyl acrylate) with a commercially available filament-type pyrolysis unit and gas chromatogaph was conducted. It has been hypothesized that the quantity of ethyl acrylate monomer produced under the conditions of the experiment is dependent upon the number of ethyl acrylate-methyl methacrylate bonds contained in the copolymer. These observations were made possible by a standardized samples-handling technique in which a uniformsize disk was pyrolyzed at a maximum pyrolysis temperature of 600°C. This enabled reproducible pyrolysis gas chromatograms to be obtained and permitted pyrolysis products of copolymers containing different ratios of ethyl acrylate and methyl methacrylate to be compared. An examination of sequence distribution data, obtained with the aid of a sequence distribution program for copolymers, showed sufficient agreement with the pyrolysis data to support the hypothesis. It has been demonstrated that pyrolysis gas chromatography may be applied to experimentally determine the sequence distribution of copolymers.
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  • 8
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The principal complication arising out of free radical-initiated polymerizations involving vinyl acetate has been the chain transfer to monomer and polymer which results in a highly branched polymer chain. Some evidence has also been presented to show that the degree of branching in polyvinyl esters increases with an increasing number of carbon atoms in the vinyl ester. It was of interest, therefore, to obtain a relative measure of the chain transfer constants for successive members of the homologous series of vinyl esters and to relate the constants to the actual structure of the respective polyvinyl ester. Accordingly, the study of the chain transfer in the benzoyl peroxideinitiated polymerizations of vinyl acetate in the presence of a homologous series of ethyl esters of fatty acids was made. Chain transfer constants versus number of carbon atoms in the carboxylate portion of the fatty acid ester resulted in a linear relationship which can be expressed as \documentclass{article}\pagestyle{empty}\begin{document}$$C_{tr,s} = 4.0 \times 10^{ - 3} + n \times 0.7 \times 10^{ - 3}$$\end{document} where n is the number of non-α-methylene groups in the side chain. A concurrent study of the influence of monomer chain lengths of selected vinyl esters on molecular weight of the derived homopolymer was also carried out. The results obtained provide a basis for predicting the trends for changes in branching and degree of polymerization within the homologous series of vinyl esters.
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