Showing papers by "Roland Benz published in 1982"

Outer membrane protein P of Pseudomonas aeruginosa: regulation by phosphate deficiency and formation of small anion-specific channels in lipid bilayer membranes.

Abstract: A new major outer membrane protein, P, was induced in Pseudomonas aeruginosa PAO1 upon growth in medium containing 0.2 mM or less inorganic phosphate. Studies with media containing different levels of phosphate and with mutants of PAO1 suggested that protein P was coregulated with alkaline phosphatase and phospholipase C. Protein P was substantially purified and shown to form sodium dodecyl sulfate-resistant oligomers on polyacrylamide gels. The incorporation of purified protein P into artificial lipid bilayers resulted in an increase of the membrane conductance by many orders of magnitude. Single-channel experiments demonstrated that protein P channels were substantially smaller than all previously studied porins from P. aeruginosa and enteric bacteria, with an average single-channel conductance in 1 M NaCl of 0.25 nS. The protein P channel was apparently not voltage induced or regulated. The results of single-channel conductance experiments, using a variety of different salts, allowed a minimum channel diameter estimate of 0.7 nm. Furthermore, from these results it was concluded that the protein P channel was highly specific for anions. Zero-current potential measurements confirmed that protein P was at least 30-fold more permeable for Cl- than for K+ ions. The possible biological role of the small, anion-specific protein P channels in phosphate uptake from the medium is discussed.

Black Lipid Membranes from Polymerizable Lipids

Abstract: The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 869. DOI:10.1002/anie.198208690

Transport Properties of Mobile Charges in Algal Membranes: Influence of pH and Turgor Pressure

Abstract: Charge-pulse experiments were performed on giant algal cells ofValonia utricularis. If the tonoplast and plasmalemma in series are charged to voltages of the order of 10mV, the decay of the initial voltage with time can be described by the sum of two or three exponential relaxations. It is not possible to explain the exponential decay of the voltage by twoRC-circuits in series (e.g. tonoplast and plasmalemma), because this would lead to unreasonable values for the specific capacities of the two membranes. The exponential relaxations might be attributable to the transport of mobile negative charges present in both membranes, possibly as a part of a transport system. From an analysis of the experimental results in terms of the proposed model, the translocation rate constantk and the total surface densityN t of the mobile charges in one membrane could be evaluated. On averagek is of the order of 600 sec−1 andNt is about 5×10−12 mol cm−2 (average turgor pressure 1.6 bar). The transport properties of the mobile charges within the tonoplast and plasmalemma were studied as a function of different parameters such as external pH, glutardialdehyde, electrical breakdown and turgor pressure. When the pH is lowered from 8.2 to 4 or 5 the mobile charges disappear completely, presumably as the result of protonation of the anionic groups. This pH effect was found to be completely reversible. Electrical breakdown causes a reversible disappearance of the relaxation with the longer half-time due to the decrease in membrane resistance. The value of the electrical breakdown voltage determined by injection of charge pulses of 300-μsec duration into the cell is pH-independent and therefore is consistent with the mobile charge model and with results previously reported (U. Zimmermann & R. Benz.J. Membrane Biol 53:33–43, 1980). Addition of glutardialdehyde leads also to a disappearance of the mobile charges probably due to cross-linkage. Increase of the turgor pressure from 0.05 bar to 2 bar results in an increase ink by a factor of 2 and inNt by about 30%. The increase ink is in reasonable agreement with that expected on the basis of the assumed compressibility of the membranes. The elastic compressive modulus perpendicular to the membrane plane calculated from the pressure dependence of the translocation rate constantk is in very good agreement with that derived from electrical breakdown experiments (14 and 13 bar, respectively). The presence of charges within the membranes as well as the compressibility of the membranes are discussed in terms of a possible turgor-pressure-sensing mechanism.

OuterMembraneProtein PofPseudomonas aeruginosa: Regulation byPhosphate Deficiency andFormation ofSmall Anion-Specific Channels inLipid Bilayer Membranes

Abstract: oligomers on polyacrylamide gels. Theincorporation ofpurified protein Pintoartificial lipid bilayers resulted inan increase of themembraneconductance bymany orders ofmagnitude. Single-channel experimentsdemonstrated thatprotein P channels were substantially smaller thanall previously studied porins fromP.aeruginosa andenteric bacteria, withan average single-channel conductance in1M NaClof0.25nS.Theprotein P channel was apparently notvoltage induced orregulated. Theresults ofsinglechannel conductance experiments, using a variety ofdifferent salts, allowed a minimumchannel diameter estimate of0.7nm. Furthermore, fromthese results it was concluded thattheprotein Pchannel was highly specific foranions. Zerocurrent potential measurements confirmed that protein Pwas atleast 30-fold more permeable forCl-thanforK+ ions. Thepossible biological roleofthesmall, anion-specific protein P channels inphosphate uptakefromthemediumis discussed.