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  • 1
    Electronic Resource
    Electronic Resource
    Role of Sterols in the Functional Reconstitution of Water-Soluble Mitochondrial Porins from Different Organisms (1995)
    s.l. : American Chemical Society
    Biochemistry 34 (1995), S. 3352-3361 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00010a026
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  • 2
    Electronic Resource
    Electronic Resource
    Single-channel analysis of the conductance fluctuations induced in lipid bilayer membranes by complement proteins C5b-9 (1986)
    Springer
    The journal of membrane biology 94 (1986), S. 37-45 
    Details
    ISSN: 1432-1424
    Keywords: complement ; lipid bilayer ; membrane ; membrane pore ; membrane conductance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Single-channel analysis of electrical fluctuations induced in planar bilayer membranes by the purified human complement proteins C5b6, C7, C8, and C9 have been analyzed. Reconstitution experiments with lipid bilayer membranes showed that the C5b-9 proteins formed pores only if all proteins were present at one side of the membrane. The complement pores had an average single-channel conductance of 3.1 nS at 0.15m KCl. The histogram of the complement pores suggested a substantial variation of the size of the single channel. The linear relationship between single-channel conductance at fixed ionic strength and the aqueous mobility of the ions in the bulk aqueous phase indicated that the ions move inside the complement pore in a manner similar to the way they move in the aqueous phase. The minimum diameter of the pores as judged from the conductance data is approximately 3 nm. The complement channels showed no apparent voltage control or regulation up to transmembrane potentials of 100 mV. At neutral pH the pore is three to four times more permeable for alkali ions than for chloride, which may be explained by the existence of fixed negatively charged groups in or near the pore. The significance of these observations to current molecular models of the membrane lesion formed by these cytolytic serum proteins is considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01901011
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  • 3
    Electronic Resource
    Electronic Resource
    Mechanism of sugar transport through the sugar-specific LamB channel ofEscherichia coli outer membrane (1987)
    Springer
    The journal of membrane biology 100 (1987), S. 21-29 
    Details
    ISSN: 1432-1424
    Keywords: LamB ; maltoporin ; lipid bilayer ; sugar transport ; transport mechanism ; membrane channel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Lipid bilayer experiments were performed with the sugar-specific LamB (maltoporin) channel ofEscherichia coli outer membrane. Single-channel analysis of the conductance steps caused by LamB showed that there was a linear relationship between the salt concentration in the aqueous phase and the channel conductance, indicating only small or no binding between the ions and the channel interior. The total or the partial blockage of the ion movement through the LamB channel was not dependent on the ion concentration in the aqueous phase. Both results allowed the investigation of the sugar binding in more detail, and the stability constants of the binding of a large variety of sugars to the binding site inside the channel were calculated from titration experiments of the membrane conductance with the sugars. The channel was highly cation selective, both in the presence and absence of sugars, which may be explained by the existence of carbonyl groups inside the channel. These carbonyl groups may also be involved in the sugar binding via hydrogen bonds. The kinetics of the sugar transport through the LamB channel were estimated relative to maltose by assuming a simple one-site, two-barrier model from the relative rates of permeation taken from M. Luckey and H. Nikaido (Proc. Natl. Acad. Sci. USA 77:165–171 (1980a)) and the stability constants for the sugar binding given in this study.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02209137
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  • 4
    Electronic Resource
    Electronic Resource
    Isolation and characterisation of porin from the outer membrane of Synechococcus PCC 6301 (1994)
    Springer
    Archives of microbiology 161 (1994), S. 163-167 
    Details
    ISSN: 1432-072X
    Keywords: Cyanobacteria ; Outer membrane ; Peptidoglycan ; associated protein ; Pore-forming protein ; Porin ; Synechococcus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Pore-forming protein (porin) was isolated from N,N-dimethyl-dodecylaminoxid (LDAO)-extracted outer membranes of Synechococcus PCC 6301 and purified by ion exchange chromatography on DEAE-Sephacel column. The apparent molecular mass on SDS-PAGE was determined to be about 52000. The native porin was reconstituted into black lipid bilayer membranes and showed a single-channel conductance of 5.5 nS in 1 M KCl. The porin was found to be N-terminally blocked. The C-terminal amino acid sequence was identified as Phe-Thr-Phe. Amino acid analysis suggested that the porin protein consists of about 420 amino acid residues, yielding a polarity of 43.6% and a molecular mass of 45000 in contrast to the mobility on SDS-PAGE.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00276478
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  • 5
    Electronic Resource
    Electronic Resource
    Isolation and characterisation of porin from the outer membrane of Synechococcus PCC 6301 (1994)
    Springer
    Archives of microbiology 161 (1994), S. 163-167 
    Details
    ISSN: 1432-072X
    Keywords: Key words: Cyanobacteria – Outer membrane – Peptidoglycan-associated protein – Pore-forming protein – Porin –Synechococcus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Pore-forming protein (porin) was isolated from N,N-dimethyl-dodecylaminoxid (LDAO)-extracted outer membranes of Synechococcus PCC 6301 and purified by ion exchange chromatography on DEAE-Sephacel column. The apparent molecular mass on SDS-PAGE was determined to be about 52 000. The native porin was reconstituted into black lipid bilayer membranes and showed a single-channel conductance of 5.5 nS in 1 M KCl. The porin was found to be N-terminally blocked. The C-terminal amino acid sequence was identified as Phe-Thr-Phe. Amino acid analysis suggested that the porin protein consists of about 420 amino acid residues, yielding a polarity of 43.6% and a molecular mass of 45 000 in contrast to the mobility on SDS-PAGE.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00276478
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  • 6
    Electronic Resource
    Electronic Resource
    Pores from mitochondrial outer membranes of yeast and a porin-deficient yeast mutant: A comparison (1989)
    Springer
    Journal of bioenergetics and biomembranes 21 (1989), S. 439-450 
    Details
    ISSN: 1573-6881
    Keywords: Yeast ; yeast mutant ; mitochondrial porin ; mitochondrial outer membrane ; lipid bilayer ; ion-channel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Reconstitution experiments were performed on lipid bilayer membranes in the presence of purified mitochondrial porin from yeast and of detergent-solubilized mitochondrial outer membranes of a porin-free yeast mutant. The addition of the porin resulted in a strong increase of the membrane conductance, which was caused by the formation of ion-permeable channels in the membranes. Yeast porin has a single-channel conductance of 4.2 nS in 1 M KCl. In the open state it behaves as a general diffusion pore with an effective diameter of 1.7 nm and possesses properties similar to other mitochondrial porins. Surprisingly, the membrane conductance also increased in the presence of detergent extracts of the mitochondrial outer membrane of the mutant. Single-channel recordings of lipid bilayer membranes in the presence of small concentration of the mutant membranes suggested that this membrane also contained a pore. The reconstituted pores had a single-channel conductance of 2.0 nS in 1 M KCl and the characteristics of general diffusion pores with an estimated effective diameter of 1.2 nm. This means that the pores present in the mitochondrial outer membranes of the yeast mutant have a much smaller effective diameter than “normal” mitochondrial porins. Zero-current membrane potential measurements suggested that the second mitochondrial porin is slightly cation-selective, while yeast porin is slightly anion-selective in the open state but highly cation-selective in the closed state. The possible role of these pores in the metabolism of mitochondria is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00762516
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  • 7
    Electronic Resource
    Electronic Resource
    Characterization of Channel-Forming Activity in Muscle Biopsy from a Porin-Deficient Human Patient (2000)
    Springer
    Journal of bioenergetics and biomembranes 32 (2000), S. 585-593 
    Details
    ISSN: 1573-6881
    Keywords: Porin deficiency ; muscle biopsy ; porin isoforms ; VDAC ; lipid-bilayer membrane ; volt age dependence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract A bioptic specimen from the muscles of a patient suffering from severe myopathy was inspected for the presence of human porin 31HL. Western blotting suggested that the specimen was free of the most abundant eukaryotic porin 31HL (HVDAC1). The specimen was treated with detergent and the soluble protein fraction was passed through a dry hydroxyapatite column. The passthrough of this column was inspected for channel formation in artificial lipid-bilayer membranes. The channel observed under these conditions had a single-channel conductance of about 2.5 nS in 1 M KCl, was cation selective, and was found to be virtually voltage independent. Experiments with a control specimen from a healthy human being, without any indication for muscle myopathy, revealed the presence of the voltage-dependent porin 31HL in the sample. It is discussed whether the patient's bioptic specimen contained another human porin, which has not been studied to date in its natural environment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005622611410
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  • 8
    Electronic Resource
    Electronic Resource
    The role of sterols in the functional reconstitution of water-soluble mitochondrial porins from plants (1996)
    Springer
    Journal of bioenergetics and biomembranes 28 (1996), S. 181-189 
    Details
    ISSN: 1573-6881
    Keywords: Mitochondrial porin ; VDAC ; Zea mays, Pisum sativum ; sterol ; reconstitution ; voltage dependence ; lipid bilayer membrane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Water-soluble porins were prepared from native mitochondrial porins isolated from different plants (pea and corn). In the water-soluble form the porins have lost their channel-forming properties. The water-soluble porins were investigated for the influence of different sterols on their membrane activity and their channel-forming properties in lipid bilayer membranes. Our experiments demonstrated that the water-soluble porins regained channel forming activity when the protein was preincubated with different sterols in the presence of a detergent. The channels formed in lipid bilayer membranes after this procedure regain in many but not all cases the original properties of the native mitochondrial porins. Preincubation with other sterols led to a change in the single-channel conductance or to a complete loss of the voltage dependence. The sterols had also a strong influence on the channel-forming activity of the porins. Preincubation of water-soluble pea porin with the plant sterol β-sitosterol resulted in a considerable higher channel-forming activity than with all the other sterols used for preincubation. The role of the sterols in the channel-forming complex is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02110649
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  • 9
    Electronic Resource
    Electronic Resource
    Mutations affecting pore formation by haemolysin from Escherichia coli (1991)
    Springer
    Molecular genetics and genomics 226 (1991), S. 198-208 
    Details
    ISSN: 1617-4623
    Keywords: Haemolysin ; Escherichia coli ; Pore formation ; Site-specific mutation ; Lipid bilayer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary By introduction of site-specific deletions, three regions in HlyA were identified, which appear to be involved in pore formation by Escherichia coli haemolysin. Deletion of amino acids 9–37 at the N-terminus led to a haemolysin which had an almost threefold higher specific activity than wild-type and formed pores in an artificial asolectin lipid bilayer with a much longer lifetime than those produced by wild-type haemolysin. The three hydrophobic regions (DI–DIII) located between amino acids 238–410 contributed to pore formation to different extents. Deletion of DI led to a mutant haemolysin which was only slightly active on erythrocyte membranes and increased conductivity of asolectin bilayers without forming defined pores. Deletions in the two other hydrophobic regions (DII and DIII) completely abolished the pore-forming activity of the mutant haemolysin. The only polar amino acid in DI, Asp, was shown to be essential for pore formation. Removal of this residue led to a haemolysin with a considerably reduced capacity to form pores, while replacement of Asp by Glu or Asn had little effect on pore formation. A deletion mutant which retained all three hydrophobic domains but had lost amino acids 498–830 was entirely inactive in pore formation, whereas a shorter deletion from amino acids 670–830 led to a mutant haemolysin which formed abnormal minipores. The conductivity of these pores was drastically reduced compared to pores introduced into an asolectin bilayer by wild-type haemolysin. Based on these data and structural predictions, a model for the pore-forming structure of E. coli haemolysin is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00273604
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  • 10
    Electronic Resource
    Electronic Resource
    Critical parameters and optimization of a magnesium-selective liquid membrane electrode for application to human blood serum (1991)
    Springer
    Fresenius' Zeitschrift für analytische Chemie 341 (1991), S. 727-731 
    Details
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The selectivity of a new magnesium ionophore (ETH 7025) induced in membranes of different compositions is experimentally studied in view of the ion activities in human serum. The required selectivity coefficient against calcium for the application of an ion-selective magnesium electrode to human serum is calculated for the worst case. Other critical parameters for the application of a liquid PVC-based ion-selective membrane to undiluted human serum discussed are: the sensor lifetime which is related to the lipophilicity of the carrier as well as the ruggedness of the membrane against interactions with components of the relatively lipophilic sample.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00321576
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