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  • 1
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 157 (1997), S. 271 -279 
    ISSN: 1432-1424
    Keywords: Key words: Mitochondria — Outer membrane — Ion flux — VDAC — Channel — Gating
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. The mitochondrial outer membrane channel, VDAC, is thought to serve as the major permeability pathway for metabolite flux between the cytoplasm and mitochondria. The permeability of VDAC to citrate, succinate, and phosphate was studied in channels reconstituted into planar phospholipid membranes. All ions showed large changes in permeability depending on whether the channel was in the open or in the low conductance, ``closed'' state, with the closed state always more cation selective. This was especially true for the divalent and trivalent anions. Additionally, the anion flux when the voltage was zero was shown to decrease to 5–11% of the open state flux depending on the anion studied. These results give the first rigorous examination of the ability of metabolites to permeate through VDAC channels and indicate that these channels can control the flux of these ions through the outer membrane. This lends more evidence to the growing body of experiments that suggest that the outer mitochondrial membrane has a much more important role in controlling mitochondrial activity than has been thought historically.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-1424
    Keywords: Key words: Electrophysiology — Insertion — Gating — NADH — Liposomes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. The channel-forming protein called VDAC forms the major pathway in the mitochondrial outer membrane and controls metabolite flux across that membrane. The different VDAC isoforms of a species may play different roles in the regulation of mitochondrial functions. The mouse has three VDAC isoforms (VDAC1, VDAC2 and VDAC3). These proteins and different versions of VDAC3 were expressed in yeast cells (S. cerevisiae) missing the major yeast VDAC gene and studied using different approaches. When reconstituted into liposomes, each isoform induced a permeability in the liposomes with a similar molecular weight cutoff (between 3,400 and 6,800 daltons based on permeability to polyethylene glycol). In contrast, electrophysiological studies on purified proteins showed very different channel properties. VDAC1 is the prototypic version whose properties are highly conserved among other species. VDAC2 also has normal gating activity but may exist in 2 forms, one with a lower conductance and selectivity. VDAC3 can also form channels in planar phospholipid membranes. It does not insert readily into membranes and generally does not gate well even at high membrane potentials (up to 80 mV). Isolated mitochondria exhibit large differences in their outer membrane permeability to NADH depending on which of the mouse VDAC proteins was expressed. These differences in permeability could not simply be attributed to different amounts of each protein present in the isolated mitochondria. The roles of these different VDAC proteins are discussed.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 99 (1987), S. 187-196 
    ISSN: 1432-1424
    Keywords: membrane ; aluminum ; channel ; mitocondrion ; voltage dependence ; VDAC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The mitochondrial outer membrane contains voltagegated channels called VDAC that are responsible for the flux of metabolic substrates and metal ions across this membrane. The addition of micromolar quantities of aluminum chloride to phospholipid membranes containing VDAC channels greatly inhibits the voltage dependence of the channels' permeability. The channels remain in their high conducting (open) state even at high membrane potentials. An analysis of the change in the voltage-dependence parameters revealed that the steepness of the voltage dependence decreased while the voltage needed to close half the channels increased. The energy difference between the open and closed states in the absence of an applied potential did not change. Therefore, the results are consistent with aluminum neutralizing the voltage sensor of the channel. pH shift experiments showed that positively charged aluminum species in solution were not involved. The active form was identified as being either (or both) the aluminum hydroxide or the tetrahydroxoaluminate form. Both of these could reasonably be expected to neutralize a positively charged voltage sensor. Aluminum had no detectable effect of either single-channel conductance or selectivity, indicating that the sensor is probably not located in the channel proper and is distinct from the selectivity filter.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-1424
    Keywords: VDAC ; Mitochondrion ; Voltage gating ; Outer membrane ; Voltage sensor ; Beta structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Yeast VDAC channels (isolated from the mitochondrial outer membrane) form large aqueous pores whose walls are believed to consist of 1 a helix and 12 β strands. Each channel has two voltage-gating processes: one closes the channels at positive potentials, the other at negative. When VDAC is reconstituted into phospholipid (soybean) membranes, the two gating processes have virtually the same steepness of voltage dependence and the same midpoint voltage. Substituting lysine for glutamate at either end of one putative β strand (E145K or E152K) made the channels behave asymmetrically, increasing the voltage dependence of one gating process but not the other. The asymmetry was the same whether 1 or 100 channels were in the membrane, indicating oriented channel insertion. However, the direction of insertion varied from membrane to membrane, indicating that the insertion of the first channel was random and subsequent insertions were directed by the previously inserted channel (s). This raises the prospect of an auto-directed insertion with possible implications to protein targeting in cells. Each of the mutations affected a different gating process because the double mutant increased voltage dependence of both processes. Thus this strand may slide through the membrane in one direction or the other depending on the gating process. We propose that the model of folding for VDAC be altered to move this strand into the sensor region of the protein where it may act as a tether and guide/restrict the motion of the sensor.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 161 (1998), S. 173-181 
    ISSN: 1432-1424
    Keywords: Key words: VDAC — Mitochondria — Outer membrane — Dehydrogenase — NADH
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. In addition to the POR1 gene, which encodes the well-characterized voltage dependent anion-selective channel (YVDAC1) of the mitochondrial outer membrane, the yeast Saccharomyces cerevisiae contains a second gene (POR2) encoding a protein (YVDAC2) with 50% sequence identity to YVDAC1. Mitochondria isolated from yeast cells deleted for the POR1 gene (Δpor1) had a profoundly reduced outer membrane permeability as measured by the ability of an intermembrane space dehydrogenase to oxidize exogenously added NADH. Mitochondria missing either YVDAC1 or both YVDAC1 and YVDAC2 showed a 2-fold increase in the rate of NADH oxidation when the outer membrane was deliberately damaged. Mitochondria from parental cells showed only a 10% increase indicating that the outer membrane is highly permeable to NADH. In the absence of YVDAC1, we calculate that the outer membrane permeability to NADH is reduced 20-fold. The low NADH permeability in the presence of YVDAC2 was not due to the low levels of YVDAC2 expression as mitochondria from cells expressing levels of YVDAC2 comparable to those of YVDAC1 in parental cells showed no substantial increase in NADH permeability, indicating a minimal role of YVDAC2 in this permeability. The residual permeability may be due to other pathways because cells missing both genes can still grow on nonfermentable carbon sources. However, YVDAC1 is clearly the major pathway for NADH flux through the outer membrane in these mitochondria.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 18 (1974), S. 315-334 
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Plasma membrane vesicles derived from Ehrlich ascites cells can accumulate 2-aminoisobutyric acid (AIB) twofold, in the absence of ion gradients or potential differences. In addition, AIB uptake is stimulated specifically by the presence of a Na+ chemical gradient (high Na+ outside). The nature of the counterion (e.g., K+, Li+, Cs+, or ethanolamine) inside the vesicle does not affect the qualitative response although quantitative differences are observed. The level of AIB present in the vesicle decreases as the Na+-gradient is dissipated. Gramicidin, which increases the rate of ion gradient dissipation, inhibits the gradient-stimulated uptake. Valinomycin stimulates AIB uptake when Na+ is present outside the vesicles and K+ is inside, probably by producing a diffusion potential which increases the electrochemical potential difference for Na+. As the Na+-gradient dissipates, AIB accumulation exceeds that predicted from 100% transfer of the energy from the Na+ chemical gradient if a 1∶1 relationship between amino acid and Na+ coupling exists. It is possible that a diffusion potential adds to the chemical gradient for Na+ making the electrochemical potential difference for Na+ adequate to energize AIB accumulation. Ouabain inhibits gradient-stimulated AIB uptake without measurable effects on the ion distributions, thus showing a direct action of ouabain on amino acid transport.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Biochimica et Biophysica Acta (BBA)/Biomembranes 1025 (1990), S. 127-134 
    ISSN: 0005-2736
    Keywords: Aluminum hydroxide ; Channel ; Metal binding site ; Mitochondrion ; VDAC ; Voltage dependence
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine , Physics
    Type of Medium: Electronic Resource
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