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  • 1
    Electronic Resource
    Electronic Resource
    Demonstration of the electrogenicity of proton translocation during the phosphorylation step in gastric H+K+-ATPase (1990)
    Springer
    The journal of membrane biology 114 (1990), S. 245-256 
    Details
    ISSN: 1432-1424
    Keywords: gastric H+K+-ATPase ; caged ATP ; pump currents ; planar lipid films
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Membrane fragments containing the H+K−-ATPase from parietal cells have been adsorbed to a planar lipid membrane. The transport activity of the enzyme was determined by measuring electrical currents via the capacitive coupling between the membrane sheets and the planar lipid film. To initiate the pump currents by the ATPase a light-driven concentration jump of ATP from caged ATP was applied as demonstrated previously for Na+K+-ATPase (Fendler, K., Grell, E., Haubs, M., Bamberg, E. 1985.EMBO J. 4:3079–3085). Since H+K+-ATPase is an electroneutrally working enzyme no stationary pump currents were observed in the presence of K+. By separation of the H+ and K+ transport steps of the reaction cycle, however, the electrogenic step of the phosphorylation could be measured. This was achieved in the absence of K+ or at low concentrations of K+. The observed transient current is ATP dependent which can be assigned to the proton movement during the phosphorylation. From this it was conclueded that the K+ transport during dephosphorylation is electrogenic, too, in contrast to the Na+K+-ATPase where the K+ step is electroneutral. The transient current was measured at different ionic conditions and could be blocked by vanadate and by the H+K+-ATPase specific inhibitor omeprazole. An alternative mechanism for activation of this inhibitor is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869218
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  • 2
    Electronic Resource
    Electronic Resource
    Size distribution of submicron particles by dynamic light scattering measurements: analyses considering normalization errors (1992)
    Springer
    European biophysics journal 21 (1992), S. 21-28 
    Details
    ISSN: 1432-1017
    Keywords: Dynamic light scattering ; Normalization errors ; Lipid vesicles ; Size distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Errors in the experimental baseline used to normalize dynamic light scattering data can seriously affect the size distribution resulting from the data analysis. A revised method, which incorporates the characteristics of this error into the size distribution algorithm CONTIN (Ruf 1989), is tested with experimental data of high statistical accuracy obtained from a sample of phospholipid vesicles. It is shown that the various commonly used ways of accumulating and normalizing dynamic light scattering data are associated with rather different normalization errors. As a consequence a variety of solutions differing in modality, as well as in width, are obtained on carrying out data analysis in the common way. It is demonstrated that a single monomodal solution is retrieved from all these data sets when the new method is applied, which in addition provides the corresponding baseline errors quantitatively. Furthermore, stable solutions are obtainable with data of lower statistical accuracy which results from measurements of shorter duration. The use of an additional parameter in data inversion reduces the occurrence of spurious peaks. This stabilizing effect is accompanied by larger uncertainties in the width of the size distribution. It is demonstrated that these uncertainties are reduced by nearly a factor of two on using the normalization error function instead of the ‘dust term’ option for the analysis of noisy data sets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00195440
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  • 3
    Electronic Resource
    Electronic Resource
    Determination of kinetic parameters from chemical relaxation data discrimination between coupled two-step binding reactions differing in stoichiometry (1994)
    Springer
    European biophysics journal 23 (1994), S. 217-226 
    Details
    ISSN: 1432-1017
    Keywords: Chemical relaxation ; Relaxation kinetics ; Two-step binding reactions ; Relaxation times ; Kinetic parameters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The chemical relaxation times of two different two-step equilibrium reactions, characterized by a 1:1 binding process followed by a subsequent rearrangement step and a stepwise 1:2 binding reaction, are analyzed for the purpose of qualitative model discrimination and quantitative determination of kinetic parameters. The equations describing the dependences of the two reciprocal relaxation times on suitable concentrations are given for both models in the general case as well as for four different limiting situations which are characterized by well separated relaxation times. The conditions corresponding to the limiting cases are expressed in terms of strong, weak and no coupling between the two partial equilibrium steps involved in both models. The coupling strength depends on the rate constants as well as on the total concentrations of the reactants. Criteria to discriminate between these two reaction models under defined limiting conditions are developed. In the general case, the product of both reciprocal relaxation times can be used to distinguish both models. If only one relaxation time can be resolved experimentally, it is possible under conditions described to determine only a reduced set of individual rate constants for most of the limiting cases considered. If both relaxation times are observed, all rate constants are determinable in the general case as well as in most of the limiting cases discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01007613
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  • 4
    Electronic Resource
    Electronic Resource
    Charge Translocation of H,K-ATPase and Na,K-ATPase (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 671 (1992), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1992.tb43794.x
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  • 5
    Electronic Resource
    Electronic Resource
    A new photometric detector in the visible spectral range based on a silicon photodiode (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 3289-3293 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: From the equivalent circuit of a photodiode it is shown that the light-induced current of the photodiode is expected to be characterized by a linear function of the light intensity in a range of eight decades. The electrical circuit of the detector based on a silicon photodiode (S1722-02; Hamamatsu) in combination with an operation amplifier used as a current-voltage converter and its realization is specified. It exhibits 10%–90% rise times between 200 ns and 5 μs depending on the internal amplification selected out of five stages. The wavelength dependence of the signal-to-noise ratio of this photodiode system is determined and compared with that of a detector based on a photomultiplier (1P28; RCA, Lancaster). At wavelengths above 580 nm the photodiode system exhibits a signal-to-noise ratio up to 20 times better than the photomultiplier system. Employing a HeNe laser as light source, a signal-to-noise ratio as high as 2×104 is found with a time resolution of 1 μs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144292
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  • 6
    Electronic Resource
    Electronic Resource
    lin-Benzo-ATP and-ADP: Versatile fluorescent probes for spectroscopic and biochemical studies (1994)
    Springer
    Journal of fluorescence 4 (1994), S. 247-250 
    Details
    ISSN: 1573-4994
    Keywords: lin-Benzo-ATP ; lin-benzo-ADP ; dissociation constants ; Mg2+ and Ca2+ binding ; fluorescence spectra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract lin-Benzo-adenine nucleotides can act not only as probes for fluorescence studies but also as structural active site probes for enzymes. To understand the basic properties oflin-benzo-ATP and-ADP, protolysis and Mg2+ and Ca2+, binding are investigated between pH 6.2 and pH 8.5 by spectrophotometric and spectrofluorometric titrations. Based on a reaction model, a set of equilibrium constants is determined which is consistent with all available experimental results. The pK values of the Mg2+ and Ca2+ complex oflin-benzo-ATP in the chosen medium are 4.6 and 4.1, respectively, and those for the corresponding diphosphate are 3.1 and 2.8, respectively. Fluorescence and absorption spectra are reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01878458
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  • 7
    Electronic Resource
    Electronic Resource
    Toward an understanding of the fluorescence intensity changes observed on fluorescein 5′-Isothiocyanate-Na+,K+-ATPase (1994)
    Springer
    Journal of fluorescence 4 (1994), S. 251-254 
    Details
    ISSN: 1573-4994
    Keywords: Fluorescence spectra ; fluorescence decay ; dissociation constants ; fluorescein 5′-isothiocyanate ; FITC-fluorescein 5′-isothiocyanate-Na+,K+-ATPase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The fluorescence emission intensity between the Na+, and the K+ complex of Na+,K+-ATPase, labeled with fluorescein 5′-isothiocyanate (FITC), differs by 30 to 40%. Experimental studies are carried out to elucidate the physical reasons which account this intensity difference. The dissociation constant of protolysis of the covalently bound FITC and its fluorescence decay times are determined in media of different ionic compositions and are compared with the corresponding properties of a synthetic model compound. The fluorophore bound to the protein is characterized by two decay times in the nanosecond range; the model compound, by a single one. The static fluorescence intensity changes are discussed on the basis of these results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01878459
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  • 8
    Electronic Resource
    Electronic Resource
    DEDO: A specific, fluorescent inhibitor for spectroscopic investigations of Na,K-ATPase (1994)
    Springer
    Journal of fluorescence 4 (1994), S. 287-290 
    Details
    ISSN: 1573-4994
    Keywords: Na,K-ATPase ; fluorescent inhibitor ; kinetics ; energy transfer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The interaction between the fluorescent ouabain derivative DEDO and purified renal Na,K-ATPase (isolated from different animal species) is investigated. Equilibrium binding studies provide a pK value of about 7.5 and a stoichoimetric coefficient of 1. Nonmodified ouabain exhibits the same affinity to the rabbit enzyme; the enzyme originating from the other sources binds DEDO 10 times less strongly than ouabain. Kinetic studies indicate that this is the consequence of a 10 times higher dissociation rate constant of the complexes formed with DEDO. The fluorescence emission intensity of DEDO is enhanced, being dependent on the enzyme source. The single decay time of DEDO is 3 ns in the absence and 21 ns in the presence of the rabbit enzyme and 14 ns in the presence of the pig renal enzyme. This result suggests that the fluorophore of DEDO is bound to a very hydrophobic environment of the enzyme. Further characterization of the static fluorescence spectra provides evidence for energy transfer between Trp residues of the enzyme and DEDO. Distance estimations suggest that one or two Trp residues are likely to be located in the proximity of the fluorophore.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01881441
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  • 9
    Electronic Resource
    Electronic Resource
    Fluorescence studies and semiempirical calculations on alkali ion indicators (1994)
    Springer
    Journal of fluorescence 4 (1994), S. 243-246 
    Details
    ISSN: 1573-4994
    Keywords: Cryptands ; alkali ion indicators ; pH sensitivity ; semiempirical calculations ; AM1
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Two newly synthesized cryptands act as sensitive Na+- and K+-selective indicators for cation concentrations above 20 μM. The fluorescence properties change markedly upon cation binding. In addition, the free ligands exhibit a pronounced sensitivity to pH, which is considerably lower for the cation complexes. Time resolved fluorescence is characterized by a decay time of about 5 ns that is attributed to the diprotonated protolytic state of the uncomplexed ligands. Semiempirical calculations show the systematic influence of the nitrogen lone pairs or the N−H bond on the stability of the system. The cause of the strong fluorescence intensity increase observed upon protonation of the fluorescent cryptands may be attributed to an increase in the S1−T x energy gap as a consequence of bridgehead nitrogen protonation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01878457
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  • 10
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    Determination of kinetic parameters from chemical relaxation data discrimination between coupled two-step binding reactions differing in stoichiometry (1994)
    Springer
    Details
    Publication Date: 1994-01-01
    Print ISSN: 0175-7571
    Electronic ISSN: 1432-1017
    Topics: Biology , Physics
    Published by Springer
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