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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Biochemistry 21 (1982), S. 4139-4143 
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Intracellular reactive iron is a source of free radicals and a possible cause of cell damage. In this study, we analyzed the changes in iron homeostasis generated by iron accumulation in neuroblastoma (N2A) cells and hippocampal neurons. Increasing concentrations of iron in the culture medium elicited increasing amounts of intracellular iron and of the reactive iron pool. The cells had both IRP1 and IRP2 activities, being IRP1 activity quantitatively predominant. When iron in the culture medium increased from 1 to 40 µm, IRP2 activity decreased to nil. In contrast, IRP1 activity decreased when iron increased up to 20 µm, and then, unexpectedly, increased. IRP1 activity at iron concentrations above 20 µm was functional as it correlated with increased 55Fe uptake. The increase in IRP1 activity was mediated by oxidative-stress as it was largely abolished by N-acetyl-l-cysteine. Culturing cells with iron resulted in proteins and DNA modifications. In summary, iron uptake by N2A cells and hippocampus neurons did not shut off at high iron concentrations in the culture media. As a consequence, iron accumulated and generated oxidative damage. This behavior is probably a consequence of the paradoxical activation of IRP1 at high iron concentrations, a condition that may underlie some processes associated with neuronal degeneration and death.
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  • 3
    ISSN: 1432-1424
    Keywords: iron uptake ; transferrin ; endocytosis ; reticulocytes ; iron mobilization ; iron translocation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The kinetics of the separate processes of Fe2(III)-transferrin binding to the transferrin receptor, transferrin-receptor internalization, iron dissociation from transferrin, iron passage through the membrane, and iron mobilization into the cytoplasm were studied by pulse-chase experiments using rabbit reticulocytes and59Fe,125I-labeled rabbit transferrin. The binding of59Fe-transferrin to transferrin receptors was rapid with an apparent rate constant of 2×105 m −1 sec−1. The rate of internalization of59Fe-transferrin was directly measured at 520±100 molecules of Fe2(III)-transferrin internalized/sec/cell with 250±43 sec needed to internalize the entire complement of reticulocyte transferrin receptors. Subsequent to Fe2(III)-transferrin internalization the flux of59Fe was followed through three compartments: internalized transferrin, membrane, and cytosol. A process preceding iron dissociation from transferrin and a reaction involving membrane-associated iron required 17±2 sec and 34±5 sec, respectively. Apparent rate constants of 0.0075±0.002 sec−1 and 0.0343±0.0118 sec−1 were obtained for iron dissociation from transferrin and iron mobilization into the cytosol, respectively. Iron dissociation from transferrin is the rate-limiting step. An apparent rate constant of 0.0112±0.0025 sec−1 was obtained for processes involving iron transport through the membrane although at least two reactions are likely to be involved. Based on mechanistic considerations, iron transport through the membrane may be attributed to an iron reduction step followed by a translocation step. These data indicate that the uptake of iron in reticulocytes is a sequential process, with steps after the internalization of Fe2(III)-transferrin that are distinct from the handling of transferrin.
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  • 4
    ISSN: 1432-1424
    Keywords: endocytic vesicles ; iron
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A59Fe assay was designed to detect an Fe(III) binding capacity in NP-40 solubilized proteins from rabbit reticulocyte endocytic vesicles. The iron binding capacity had an apparent molecular weight as determined by gel exclusion chromatography of 450,000 daltons. The iron binding moiety coincided with the major nontransferrin iron-containing material of endocytic vesicles labeled in vivo by incubation of cells with59Fe,125I-labeled transferrin. The material solubilized from vesicles with NP-40 exhibited two classes of saturable binding sites, one with an association constant for59Fe-citrate of 3.63×109 m −1 and with 6.6×10−12 moles of iron bound per mg protein and the other with a constant of 3.96×108 m −1 and 1.0×10−12 moles of iron bound per mg protein. These affinities are sufficient to satisfy the sobulility characteristics of Fe(III) at pH 5.0. Most of the59Fe bound both in vivo and in vitro to the iron binding moiety could be displaced with56Fe and an equivalent amount of59Fe could subsequently be rebound in vitro. The iron binding assay was adopted to vesicle proteins separated by SDS-polyacrylamide gel electrophoresis with subsequent transfer to nitrocellulose and revealed an iron binding activity of molecular weight approximately 95,000 daltons.
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  • 5
    ISSN: 1573-6881
    Keywords: Acidification ; endocytic vesicle ; Na+ fluxes ; Cl− fluxes ; H+ fluxes ; H+-ATPase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract The ionic fluxes associated with the ATP-dependent acidification of endocytic vesicles were studied in a preparation isolated from rabbit reticulocytes enriched for transferrin-transferrin receptor complexes. No vesicle acidification was observed in the absence of intra- and extravesicular ions (sucrosein/sucroseout), while maximal acidification was observed with NaClin/KClout·K in + was a poor substitute for Na in + , and Cl out − could be replaced by other anions with the following efficacy of acidification: Cl−〉Br−〉I−〉PO 4 3− 〉gluconate〉SO 4 2− . Flux studies using36Cl− and22Na+ showed that the vesicles had a permeability for Cl− and Na+, and that ATP-dependent H+ pumping was accompanied by a net influx of Cl− and a net efflux of Na+ provided that there was a Na+ concentration gradient. After 3 mins, the time necessary to maximal acidification, the electrical charge generated by the entrance of H+ was countered to about 45% by the Cl− influx and to about 42% by the Na+ efflux. These studies demonstrated that both Cl− and Na+ fluxes are necessary for optimal endocytic vesicle acidification.
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  • 6
    ISSN: 1573-6881
    Keywords: Iron ; transferrin ; reduction ; endosome ; ascorbate ; NADH ; transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Externally added ascorbate or NADH effectively reduced ferricyanide and promoted the exit of Fe3+ originated from acid-destabilized transferrin contained inside endocytic vesicles. The effect of ascorbate was mediated by an ascorbate uptake system, and the effect of NADH was mediated by the membrane-associated oxidoreductase. At physiological concentrations of both ascorbate and NADH, the ascorbate transport and the NADH-oxidoreductase system were additive as measured by the rate of reduction of ferricyanide and by the mobilization of transferrin-associated iron. The results indicate that Fe3+ reduction may occur by a nonenzymatic reaction with ascorbate transported into the vesicle lumen. The ascorbate-mediated reduction of iron derived from transferrin occurring in the endosome could play a major role in cellular iron uptake.
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  • 7
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A numerical method is developed to obtain a sequence of functions converging to the eigenfunctions of the Schrödinger operator H = - ½ Δ + V(r) for V(r) = - Z/r + χ(r), where χ(r) is a continuous and bounded-from-below function for (r ∊ 0, ∞). The criterion of convergence in the convergence in the norm of the Hilbert space L2(0, ∞), which assures the accurate computation of the expected values for a symmetric operator, as we show. The method consists of solving the dirichlet problem inside a box of radius n by the Ritz method, whose convergence in the norm is proved using the compactness criterion. Using a physical argument, we show that the bounded states of the Dirichlet problem converge to those the unbounded system in the norm of L2(0, ∞) as n grows. The method is applied to the potentials V(r) = - Z/r + ari (i ≥ 0) and V(r) = - Z/r + a/(1 + rλ); in each case, we show the numerical convergence of eigenfunctions, energies, and density moments. © 1994 John Wiley & Sons, Inc.
    Additional Material: 14 Tab.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method developed previously for computing eigenfunctions of one-dimensional Schrödinger operators is extended to Schrödinger operators in L2(R3N). It is known that in many cases these operators have not a compact resolvent; therefore, the convergence in L2(R3N) of the more used methods for computing the eigenfunctions is not guaranteed. The idea of the present method consists of replacing the eigenvalue problem in L2(R3N) by one corresponding to the system confined into a box Ω with impenetrable walls [Dirichlet problem in L2(Ω)]. It is shown that the eigenfunctions of the unbounded system can be approximated by those of the confined system when the box Ω is expanded. On the other hand, it is proved that the Schrödinger operator associated to the confined system has a compact resolvent and its corresponding sesquilinear form is bounded and elliptic in the Sobolev space W2,10(Ω). These properties guarantee the convergence in L2(Ω) of the standard methods to solve the Dirichlet problem: the Ritz method as well as the finite-element and finite-difference methods. Therefore, the eigenfuncions of the unbounded system can be approximated in L2(R3N) by means of the numerical solutions of the Dirichlet problem in L2(Ω) with sufficiently large Ω. This property guarantees the accurate computation of the true expectation values. © 1994 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 57 (1996), S. 1077-1096 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The role of the asymptotic behavior of approximating sequences of electron densities ρn(r) in the calculation of one-electron properties is studied. Rigorous mathematical results in the frame of Hilbert spaces are used to prove the following facts: (i) Both the L2 convergence of wave functions ψn and the E convergence of the corresponding energies En guarantee the correctness of the limiting procedure limn→x ∫Ω s((overline)x(/overline)|ψn|2 d(overline)x(/overline) = ∫Ω s((overline)x(/overline))|ψ|2 d(overline)x(/overline) for the most frequently used operators s(x), Ω being any bounded region of the n-particle configuration space R3N; and (ii) the uniform boundedness of the sequence {ρn} together with both the L2 and E convergencies is sufficient to guarantee the correctness of the limiting procedure limn→x ∫∞0 s(r)ρnr2dr = ∫x0 s(r)ρr2 dr for most one-electron operators s(r) including the power moment operators rk which, for large k, are representative of the class of operators not relatively form-bounded by the Hamiltonian. The mathematical concept of uniform boundedness is used to give a characterization of the capability of {ρn} to reproduce the asymptotic behavior of the true electron density ρ and it is shown by means of numerical examples how a sequence {ρn} that does not reproduce the correct asymptotic behavior is not uniformly bounded and can give divergent expectation values of one-electron operators s(r) not relatively form-bounded by the Hamiltonian. © 1996 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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