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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1573-6881
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1573-6881
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract The pH-dependent changes in structure of submitochondrial vesicles prepared from rat liver have been investigated by a variety of structural “probes”. The main changes are: (a) the volume of the vesicles as assessed by electron microscopy and packed volume is dependent upon pH, being a minimum at pH 5. Between pH 5 and pH 9 the changes are reversible; (b) the accompanying light-scattering changes are also sensitive to divalent cations; (c) the binding characteristics of 8-anilinonaphthalene-1-sulfonic acid indicate pH-dependent changes in the amount of net charge on the membrane; (d) above pH 4, circular dichroism spectra show alterations characteristic of changes in quaternary protein structure; (e) below pH 4, infrared studies indicate changes in protein secondary conformation are also taking place. From these results, the nature and limits of conformational (molecular) and configurational (morphological) changes in mitochondrial membranes following changes in H+ activity are better defined. In the physiological range, pH-dependent conformational changes are confined to reversible changes in quaternary structure resulting from alterations in membrane charge.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1573-6881
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Bovine adrenal cortex mitochondria examined by electron microscopyin situ orin vitro in 0·25 M sucrose have an unusual cristal membrane structure. The cristae usually appear as unconnected vesicles within a double membrane system. A few of the vesicles appear to be attached to the inner boundary membrane or to one or more other vesicles. The configuration of such mitochondria will be defined as the orthodox configuration. In this communication we will provide evidence that the inner membrane is not composed of multiple vesicles, but is one continuous membrane with tubular invaginations, and that these invaginations alternately are ballooned out and squeezed down. A mechanism has been proposed to account for the differentiated structure of the cristae of adrenal cortex mitochondria.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1573-6881
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    Location Call Number Limitation Availability
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1573-6881
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Bovine adrenal cortex mitochondria when isolated in a medium 0·25 M in sucrose contaminated (with calcium) have tubular cristae which are periodically expanded to spherical vesicles and contracted to flattened connecting sections. This scalloped tubular form of the cristae corresponds to the nonenergized orthodox configuration—a configuration in which the matrix space is maximally expanded. When adrenal cortex mitochondria are isolated in media in which the free calcium content is relatively low, e.g., a medium 0·25 M in sucrose and 0·1 mM in EDTA, the cristae assume the aggregated configuration—a nonenergized configuration in which the matrix space is maximally contracted. The composition of the isolation medium determined the configuration. Procedures have been described for isolating bovine adrenal cortex mitochondria (a) predominantly in the orthodox configuration, (b) predominantly in the aggregated configuration, or (c) in a mixed (1∶1) population of configurations. The concentration of Ca2+ bound to the mitochondrion was found to be a determinant of the nonenergized configuration. When the level of bound Ca++ was 20–25 μmoles/mg protein, the cristae of the mitochondria were entirely in the orthodox configuration. Addition of Ca2+ could induce the transition of cristae from the aggregated to the orthodox configuration whereas addition of Mg2+ could induce the transition of cristae from the orthodox to the aggregated configuration. The configurational transition could be followed by any of several methods—a change in 90° light scattering, a change in O.D.520 mμ, a change in pH, or examination by electron microscopy. The orthodox to aggregated transition is energy-independent since it proceeds even in presence of inhibitors both of electron transfer and of ATP hydrolysis. The binding of Ca2+ is independent of the binding of Mg2+; this independent binding is consistent with the opposite effects induced by Ca2+ and Mg2+, respectively. Whereas Ca2+ induces a proton release, a decrease in 90° light scattering and a decrease in O.D.520 mμ (when the cristae are initially in the aggregated configuration), Mg2+ induces equal and opposite changes (when the cristae are initially in the orthodox configuration).
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1573-6881
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Analysis of lumiflavin triplet-state decay kinetics in aqueous solution has given the following results:k 1 (first-order decay)=670 sec−1,k 2 (triplet-triplet quenching)=8·9×108 M−1 sec−1,k 3 (triplet-ground-state quenching)=3·7×108 M−1 sec−1. The FMN triplet decays mainly via intramolecular quenching by the ribityl side chain and triplet-groundstate quenching. Ferricyanide and phenols are shown to be excellent quenchers of the flavin triplet (comparable to KI and O2). In the case of phenols, quenching occurs via hydroxyl hydrogen abstraction to generate flavin radical and phenoxy radical. Recombination of these radicals (by reverse hydrogen transfer) competes effectively with flavin radical disproportionation. The lumiflavin triplet is also able to abstract hydrogen from a ground state lumiflavin molecule (probably from the 10-methyl group). The radicals so generated can either recombine or undergo a buffer-catalyzed reaction leading to permanent bleaching. Evidence is presented for rapid oxidation of lumiflavin radical by both oxygen and ferricyanide. In dry non-polar solvents, lumiflavin triplet formation is prevented; addition of small amounts of water restores the ability to produce triplet state molecules. This is probably due to an effect of water on intersystem crossing.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1573-6881
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Further evidence is presented as to the distribution of the four major cations in biological systems: sodium, potassium, calcium, and magnesium. A relationship between ATPase activity and the cation balances is examined, but as the ATPase activity is itself dependent upon ion gradients the steady state of a cell must be dependent upon the ATPase enzyme concentration, the ion concentrations which it helps to maintain, and the availability of ATP. The effect of the product of these three terms upon the stability of fibosomes and other structures is pursued and its ramifications in cell growth (protein synthesis) and electrical activity discussed. Consequential effects, which could be linked with differentiation and retention of information in such structures as the brain, are also considered.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1573-6881
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1573-6881
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Mitochondria from rat heart, liver, and skeletal muscle, when isolated in a medium containing 10 mM EDTA, showed poor respiratory control and large volume changes in the presence of ATP or oxidizable substrates. Swelling required the presence of alkali metal cations and permeant anions and probably reflects ion transport. As shown previously for skeletal muscle mitochondria, addition of Mg2+ prevents major volume changes and also imposes control of respiration by phosphorylation. Addition of Mg2+ after ATP-energized swelling caused shrinkage of the mitochondria back to the original state. This reversal of swelling is energized by ATP, but not by substrate (when ATP synthesis is inhibited by oligomycin). Electron micrographs showed that the matrix space of mitochondria from all three sources expands during the swelling process. In addition, cristal membranes showed several three-dimensional arrangements. In the contracted state which existed in presence of ATP+Mg2+, cristae of muscle mitochondria appeared “sheetlike”, whereas in presence of substrates many of these cristae assumed a “tubular” appearance. The structural changes in liver mitochondria under these conditions appeared similar to those of muscle mitochondria, but because of the greater proportion of matrix in liver mitochondria, the terms “sheetlike” and “tubular” are less descriptive of the situation. A transition from tubular to sheetlike appearance occurred upon addition of either ATP or ADP to respiring mitochondria in presence of added substrates and phosphate. This transition required Mg2+ and may involve the same mechanism that brings about reversal ofswelling. The implications of these studies are discussed in relation to proposed mechanisms of odixative phosphorylation.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1573-6881
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract The electron affinity and ionization potential of various biological substances were measured by polarography and compared with their effect on growth ofE. coli.
    Type of Medium: Electronic Resource
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