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  • 1
    Electronic Resource
    Electronic Resource
    Patch clamping the outer mitochondrial membrane (1987)
    Springer
    The journal of membrane biology 97 (1987), S. 21-29 
    Details
    ISSN: 1432-1424
    Keywords: mitochondrial outer membrane ; channels ; VDAC ; porin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Intact giant mitochondria isolated from the liver of mice fed a diet containing cuprizone were studied using patch microelectrodes. The current-voltage curves were nonlinear, suggesting the presence of voltage-sensitive channels. In the negative range of voltage, the channels appear to close with increasing magnitude of the voltage. The dependence of the conductance on voltage is similar to that of the outer membrane channels (VDAC) studied in planar bilayers. Occasionally, over a narrow range of positive potentials, the conductance also decreases as in the bilayer studies. However, more frequently the conductance increases sharply in a completely reversible manner at potentials greater than 10 to 20 mV. The increase in conductance with voltage may be interpreted as a major rearrangement of membrane components. Qualitatively comparable results were obtained using fused outer membranes isolated fromNeurospora mitochondria. The behavior of VDAC is affected by treatment with succinic anhydride or the polyanion, polymethacrylate, maleate, styrene (1∶2∶3). We have found similar effects in the negative range of potentials in patches from giant mitochondria treated in the same fashion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869611
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  • 2
    Electronic Resource
    Electronic Resource
    Interrelatedness of 5S RNA sequences investigated by correspondence analysis (1987)
    Springer
    Journal of molecular evolution 24 (1987), S. 228-235 
    Details
    ISSN: 1432-1432
    Keywords: 5S RNA ; Correspondence analysis ; Multivariate statistics ; Evolution ; Phylogeny
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Correspondence analysis (a form of multivariate statistics) applied to 74 5S ribosomal RNA sequences indicates that the sequences are interrelated in a systematic, nonrandom fashion. Aligned sequences are represented as vectors in a 5N-dimensional space, where N is the number of base positions in the 5S RNA molecule. Mutually orthogonal directions (called factor axes) along which intersequence variance is greatest are defined in this hyperspace. Projection of the sequences onto planes defined by these factorial directions reveals clustering of species that is suggestive of phylogenetic relationships. For each factorial direction, correspondence analysis points to regions of “importance”, i.e., those base positions at which the systematic changes occur that define that particular direction. In effect, the technique provides a rapid determination of group-specific signatures. In several instances, similarities between sequences are indicated that have only recently been inferred from visual base-to-base comparisons. These results suggest that correspondence analysis may provide a valuable starting point from which to uncover the patterns of change underlying the evolution of a macromolecule, such as 5S RNA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02111236
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  • 3
    Electronic Resource
    Electronic Resource
    Electron Tomographic and Ultrastructural Analysis of the Cryptosporidium parvum Relict Mitochondrion, its Associated Membranes, and Organelles (2005)
    Oxford, UK : Blackwell Science Inc
    The @journal of eukaryotic microbiology 52 (2005), S. 0 
    Details
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Sporozoites of the apicomplexan Cryptosporidium parvum possess a small, membranous organelle sandwiched between the nucleus and crystalloid body. Based upon immunolabelling data, this organelle was identified as a relict mitochondrion. Transmission electron microscopy and tomographic reconstruction reveal the complex arrangement of membranes in the vicinity of this organelle, as well as its internal organization. The mitochondrion is enveloped by multiple segments of rough endoplasmic reticulum that extend from the outer nuclear envelope. In tomographic reconstructions of the mitochondrion, there is either a single, highly-folded inner membrane or multiple internal subcompartments (which might merge outside the reconstructed volume). The infoldings of the inner membrane lack the tubular “crista junctions” found in typical metazoan, fungal, and protist mitochondria. The absence of this highly conserved structural feature is congruent with the loss, through reductive evolution, of the normal oxidative phosphorylation machinery in C. parvum. It is proposed that the retention of a relict mitochondrion in C. parvum is a strategy for compartmentalizing away from the cytosol toxic ferrous iron and sulfide, which are needed for iron sulfur cluster biosynthesis, an essential function of mitochondria in all eukaryotes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1550-7408.2005.04-3317.x
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  • 4
    Electronic Resource
    Electronic Resource
    Electron microscopy and image analysis of the mitochondrial outer membrane channel, VDAC (1987)
    Springer
    Journal of bioenergetics and biomembranes 19 (1987), S. 329-340 
    Details
    ISSN: 1573-6881
    Keywords: Mitochondrial outer membrane ; channel ; electron microscopy ; image processing ; negative stain ; frozen-hydrated ; succinic anhydride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract The channel protein in the outer membrane ofNeurospora crassa mitochondria, VDAC, forms extended planar crystals on the membrane. The arrays, which are induced by phospholipase A2, are polymorphic, varying from parallelogram (P) to near-rectangular (R) geometry with increased phospholipase treatment. Computer-based analysis of projection images of negatively stained VDAC arrays indicates that the protein forms a transmembrane channel in the P array. Comparison of average images of arrays embedded in different negative stains suggests that the bore of the channel is 2–2.5 nm. The locations of functionally important lysine clusters on VDAC are inferred from the effects of succinylation on projection images of arrays negatively stained with phosphotungstate. Projection images of unstained frozen-hydrated arrays indicate the general shape of the channel and suggest each channel is formed by one 31-kDa VDAC polypeptide.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00768536
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  • 5
    Electronic Resource
    Electronic Resource
    Structure of the mitochondrial outer membrane channel derived from electron microscopy of 2D crystals (1989)
    Springer
    Journal of bioenergetics and biomembranes 21 (1989), S. 427-437 
    Details
    ISSN: 1573-6881
    Keywords: Mitochondrial outer membrane ; channel ; electron microscopy ; image processing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract A structural model for the channel in the mitochondrial outer membrane is presented, derived from electron microscopic studies of two-dimensional crystals and inferences from the primary structure of the 30-kDa polypeptide which forms the channel. The channel is represented as a cylindrical beta-barrel, with a carbon backbone diameter of 3.8 nm. The axial projection of the cylinder is divided radially into four sectors by four interchannel contact points. These sectors are characterized in terms of their interactions with lipid and macromolecular ligands, and in terms of the presence or absence of exposed basic amino acids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00762515
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  • 6
    Electronic Resource
    Electronic Resource
    Properties of channels in the mitochondrial outer membrane (1989)
    Springer
    Journal of bioenergetics and biomembranes 21 (1989), S. 451-459 
    Details
    ISSN: 1573-6881
    Keywords: Mitochondrial outer membrane ; mitochondrial channels ; patch clamping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Patch-clamping studies with native outer mitochondrial membranes show a complex behavior. In the range of potentials in which the polarity of the pipette is positive, the behavior resembles that of VDAC incorporated into bilayers. Accordingly, there is a decrease in conductance with voltage. An involvement of VDAC is also supported by responses of the patches to the presence of polyanion or treatment with succinic anhydride, both of which affect VDAC. In contrast, in the negative range of potential, the conductance of the patches generally increases with the magnitude of the voltage. The increase in conductance shows a biphasic time course which is consistent with a model in which channels are first activated (first phase) and then assembled into larger high-conductance channels (second phase). A variety of experiments support the notion that an assembly takes place. The time course of the conductance increase is consistent with formation of the second-phase channels from 6±1 subunits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00762517
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  • 7
    Electronic Resource
    Electronic Resource
    Binding of a synthetic targeting peptide to a mitochondrial channel protein (1992)
    Springer
    Journal of bioenergetics and biomembranes 24 (1992), S. 55-61 
    Details
    ISSN: 1573-6881
    Keywords: Mitochondrial channels ; mitochondrial targeting sequences ; electron microscopy ; computer image processing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Membrane crystals of the mitochondrial outer membrane channel VDAC (porin) fromNeurospora crassa were incubated with a 20-amino-acid synthetic peptide corresponding to the N-terminal targeting region of subunit IV of cytochrome oxidase. The peptide caused disordering and contraction of the crystal lattice of the membrane arrays. Also, new stain-excluding features were observed on the peptide-treated arrays which most likely correspond to sites at which the peptide accumulates. The stain exclusion zones associated with binding of the targeting peptide (and with binding of apocytochromec in an earlier study) have been localized on a two-dimensional density map of frozen-hydrated, crystalline VDAC previously obtained by cryo-electron microscopy. The results indicate that both the peptide and cytochromec bind to protein “arms” which extend laterally between the channel lumens. The finding that imported polypeptides bind to a specific region of the VDAC protein implicates this channel in the process by which precursor proteins are recognized at and translocated across the mitochondrial outer membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00769531
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  • 8
    Electronic Resource
    Electronic Resource
    Importance of the mitochondrial outer membrane channel as a model biological channel (1987)
    Springer
    Journal of bioenergetics and biomembranes 19 (1987), S. 305-308 
    Details
    ISSN: 1573-6881
    Keywords: Mitochondrial outer membrane channels ; permeability ; voltage gating ; ion selectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract The channels of the mitochondrial outer membrane represent a useful model for studies into the mechanisms underlying phenomena of voltage-dependent gating and ion selectivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00768533
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  • 9
    Electronic Resource
    Electronic Resource
    Molecular genetics of the VDAC ion channel: Structural model and sequence analysis (1987)
    Springer
    Journal of bioenergetics and biomembranes 19 (1987), S. 341-350 
    Details
    ISSN: 1573-6881
    Keywords: Yeast VDAC ; gene cloning ; secondary structure ; bacterial porins ; sequence homology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract The voltage-dependent anion-selective channel of the outer mitochondrial membrane provides a unique system in which to study the molecular basis of voltage gating of ion flow. We have cloned and sequenced acDNA coding for this protein in yeast. From the derived amino acid sequence, we have generated a preliminary model for the secondary structure of the protein which suggests that the protein forms a “β-barrel” type structure. Comparison of the VDAC amino acid sequence with that of the bacterial porins has indicated that the two classes of molecules appear to be unrelated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00768537
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  • 10
    Electronic Resource
    Electronic Resource
    Toward the molecular structure of the mitochondrial channel, VDAC (1992)
    Springer
    Journal of bioenergetics and biomembranes 24 (1992), S. 7-19 
    Details
    ISSN: 1573-6881
    Keywords: Mitochondrial outer membrane ; VDAC ; membrane channel ; voltage gating ; electron microscopy ; membrane crystals ; site-directed mutagenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract A summary is presented of the most recent information about the structure and mechanism of closure of the mitochondrial channel, VDAC. Considerable information has come from studies involving electron microscopy of two-dimensional crystals and from electrophysiological studies of wild-type channels and site-directed mutants. Available evidence points to a β-barrel as the basic structural model for VDAC. Two models for voltage- or effector- induced closure have been proposed, the first involving removal of strands from the wall of the pore, the second invoking movement of protein domains into the lumen. Experimental strategies to resolve the actual mechanism are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00769525
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