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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    European biophysics journal 1 (1974), S. 47-54 
    ISSN: 1432-1017
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract A necessary criterion has been obtained for the occurrence of oscillating reactions in multi-enzyme systems with end-product inhibition. Computer-simulations strongly suggest that this criterion is also sufficient, since limit-cycles arise whenever the criterion is violated with a cycle-time in good agreement with the theoretically derived estimate.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    European biophysics journal 1 (1974), S. 1-16 
    ISSN: 1432-1017
    Keywords: Selectivity ; Tetrodotoxin ; TEA ; Channel Density ; Gating Function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Ionic channels are discrete sites at which the passive movement of ions takes place during nervous excitation. Three types of channels are distinguished. 1. Leakage channels that are permanently open to various cations. 2. Na channels that open promptly on depolarization but slowly close again (inactivate) on sustained depolarization and that are predominantly permeable to Na+ ions. 3. K channels that on depolarization open after some delay but stay open and that are mainly passed by K+ ions. The selectivity sequence of the Na channels of the squid axon (or frog nerve) is as follows: Na+ ≈ Li+〉(T1+)〉NH+ 4≫K+〉 Rb+, Cs+; that of K channels is: (T1+)〉K+〉Rb+〉NH+ 4≫Na+, Cs+, Na channels are selectively blocked by tetrodotoxin (TTX) or saxitoxin (STX), K channels by tetraethylammonium ions (TEA). Either channel type is reversibly blocked when one drug molecule binds to one site per channel, the equilibrium dissociation constant of these reactions being about 3×10−9 MTTX (or STX) and 4×10−4 M TEA, respectively. Because of their specificity and high affinity, TTX and STX are used to “titrate” the Na channels whose density appears to be of the order of 100/Μm2. The “gates” of the channels operate as a function of potential and time but independent of the permeating ion species. Drugs (e.g. veratridine) and enzymes (e.g. pronase, applied intraaxonally) cause profound changes in the gating function of the Na channels without influencing their selectivity. This points to separate structures for gating and ion discrimination. The latter is thought to be, in part, brought about by a “selectivity filter” of which detailed structural ideas exist. Recent experiments suggest that the gates of the Na channels are controlled by charged particles moving within the membrane under the influence of the electrical field.
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  • 3
    ISSN: 1432-1017
    Keywords: Native DNA ; Denatured DNA ; DNA Adsorption ; DNA Reduction ; Helix-Coil Transition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The adsorption and the reduction of native and denatured DNA has been studied at the hanging mercury drop electrode (HMDE) by triangular sweep polarography. It has been established from the dependence of the reduction peak of denatured DNA (Fig. 2) on the waiting time at the starting potential E8 of the sweep (Fig. 3) where the adsorption takes place and on pH (Fig. 4) that a protonated form of denatured DNA is reduced from the adsorbed state in a totally irreversible electrode process at a pH lower than 7.5. From the logarithmic analysis of the beginning part of the reduction peak the charge transfer rate constant and the charge transfer coefficient were determined (Fig. 5). The reduction products are interconnected to a high molecular network strongly adhering to the surface of the electrode and blocking it for a repeated reduction on the same drop. In neutral media the protonation of DNA becomes rate-determining. The adsorption is diffusion controlled and from the time dependence of the coverage the diffusion coefficient of DNA could be estimated (Fig. 6) to 5.10−7 cm2 s−1 in 1 M KCl at 25
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  • 4
    ISSN: 1432-1017
    Keywords: Fluorescence ; Nerves ; Bilayers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Changes in extrinsic fluorescence intensity, associated with step changes in membrane potential, have been studied in intracellularly or extracellularly stained squid axons, and in lipid bilayers, using six different aminonaphthalene dyes: 1,8-TNS; 2,6-TNS; 1,8-MANS; 2,6-MANS; 2,6-ANS and NPN. In all preparations the optical signals were found to be roughly proportional to the voltage applied. All signals had a very fast initial component, which was followed in some case by a slower change in the same direction. The slow component was observed only in intracellularly stained axons, and not for all chromophores studied. 1,8-TNS, 1,8-MANS and 2,6-MANS yielded the largest fluorescence signals in all preparations. The sign of these signals was independent of the type of membrane studied. However, the fluorescence changes of 2,6-MANS were opposite to those of 1,8-TNS and 1,8 MANS. Staining of both sides of the axolemma with 1,8-MANS or 2,6-MANS showed that these dyes yield larger signals when applied to the extracellular face. The changes in fluorescence light intensity of 2,6-TNS, 2,6-ANS and NPN were smaller and their sign depended on the membrane preparation studied. The comparison of the extrinsic fluorescence signals from the nerve membrane and the phosphatidylcholine bilayer suggests strong similarities between the basic structures of the two systems. The variety of observed signals cannot be easily interpreted in terms of changes in membrane structure. A possible alternative interpretation in terms of electrically induced displacements, rotations and changes in partition coefficient of bound chromophores, is discussed.
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  • 5
    ISSN: 1432-1017
    Keywords: Lutein ; Chlorophyll-a ; Energy-Transfer ; Micelles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Absorption, fluorescence and fluorescence excitation spectra were determined for equimolar mixed micellar detergent solutions of lutein and chlorophyll-a in the concentration range from 9·10−6 to 1.8·10−4 M, with detergent (triton-X100) concentrations from 3·-10−4 to 7·10−3 M. In the range of detergent concentrations studied the pigments incorporated into the detergent micelles attained a high local concentration (0.1 to 0.01 M), reminiscent of pigment concentration within the chloroplast. A lutein → chlorophyll-a energy transfer with an efficiency of about 15% was found in these systems. In dilute (9·10−6 M) pigment solution with concentrated (7·10−3 M) detergent practically no transfer is observed. The extent of aggregation and the efficiency of transfer depend on the composition of the system. The aggregation of chlorophyll-a is partly inhibited by lutein molecules. It is shown that the energy transfer efficiency as function of distance follows anr −3 relationship,R 0 being 22 å.
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  • 6
    ISSN: 1432-1017
    Keywords: Calorimetry ; Circular Dichroism ; Flagellin ; Polymerization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The heat effects accompanying the isothermalin vitro polymerization ofPr. mirabilis flagellin on short flagella fragments (seeds) have been measured in phosphate buffer pH 7, at various temperatures employing a batch microcalorimeter. Additionally, at 20
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  • 7
    ISSN: 1432-1017
    Keywords: Langmuir-Blodgett Layers ; Instability ; Crystallization ; Electron Microscopy ; Infrared Spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Results of an investigation of the stability of n-layers of barium stearate, cadmium arachidate and tripalmitin by means of electron microscopy and attenuated total reflection infrared spectroscopy are reported. Odd and even numbered barium stearate n-layers with n=1,2,3.4,5 are found to rearrange spontaneously from a regular film into ultrastructures of irregular, flat islands of varying thickness. The kinetics of the phase transformation of the first layer depends on the substrate, that of n-layers appears to be dependent on n, the temperature, and the surrounding medium. The kinetic behaviour of odd and even numbered layers is distinctly different. Similar studies on cadmium arachidate layers reveal much slower kinetics of the rearrangement process. In the case of tripalmitin n-layers it is shown that electron microscopy and infrared spectroscopy yield valuable complementary information about ultrastructure and molecular structure of the layers in correlation with the rearrangement process, which also occurs with this system. Consequences of the results of this paper for work published in various fields are briefly discussed.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    European biophysics journal 1 (1975), S. 97-111 
    ISSN: 1432-1017
    Keywords: Electron Transport ; Cytochrome C ; Kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The kinetics of reduction of horse heart cytochrome c have been investigated using the reductants sodium dithionite and potassium ferrocyanide. Sodium dithionite reduction at pH 7.0 yields rate constants of 2.8×108M−1sec−1 for SO 2 − and 6×105M−1sec−1 for S2O 4 = at infinite dilution. Moreover,the data presented demonstrates the participation of positively charged amino acid side chains at the site of electron transfer. The effect of pH on the reduction of ferricytochrome c requires a minimum of two pK Values for description (pK1=7.0±0.4,pK2=9.3±0.3). Based on the pK values determined, one or more lysines and a residue(s) with a low pK are implicated as the positively charged residues participating in electron transfer. From a comparison of the rates of reduction of various denatured forms of cytochrome c we feel that the most viable conclusion is that electron transfer takes place at the exposed heme edge in the vicinity of the amino acid side chains indicated above. Ferrocyanide reduction of ferri-horse heart cytochrome c takes place in a kinetically complex manner. A mechanism is described which includes complexes of ferrocyanide and ferricytochrome c and ferricyanide and ferrocytochrome c. As was found for dithionite reduction a positively charged region of the cytochrome c participates in electron transfer. Combining our results with ferrocyanide and dithionite we conclude that available data is compatible with a single mechanism of electron transfer. It is suggested that the kinetic distinction between different reductants lies in the lifetime of the transient complex formed, with the order ferrocyanide≫ S2O 4 = 〉SO 2 − .
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  • 9
    ISSN: 1432-1017
    Keywords: Stacking ; selfassociation ; NMR ; Isodesmic Model ; Enthalpy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The selfassociation of N6,N9-dimethyladenine and N6-dimethyl-N9-ethyladenine has been studied by means of NMR technique. The thermodynamic quantities have been calculated using an isodesmic NMR model with three NMR parameters (the monomer shift δM and two complex shifts δ 2 and δ 3). The dependence of the thermodynamic quantities on the NMR parameters is discussed. Special attention is given to the determination of δ M and its temperature dependence. Calculations with δ 3=2·δ 2 and δ M taken independently of temperature result in an average entropy δ S =−17.9±1.8 e.u. for N6,N9-dimethyladenine and δ S =−16.7±1.7 e.u. for N6-dimethyl-N9-ethyladenine and in an average enthalpy δH=−7.2±0.6 kcal· mol−1 for both substances investigated.
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  • 10
    ISSN: 1432-1017
    Keywords: CT-Interactions ; Metal Ions ; Uracil Derivatives ; ESR ; Optical Absorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The interaction between Cu2+ and a few uracil derivatives has been investigated by means of electron spin resonance and optical absorption studies. It could be shown that a charge transfer interaction occurs. Its strength depends upon the electron attracting or releasing properties of the substituents of the nucleobase.
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