Dimerization constant and single-channel conductance of Gramicidin in thylakoid membranes

Schönknecht, Gerald; Althoff, Gerd; Junge, Wolfgang

doi:10.1007/bf00232323

Cited by 15 publications

(8 citation statements)

References 22 publications

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“…The use of the ruby laser avoided double hitting in the presence of the oxidized nonheme iron at the PSII acceptor side. Transients that where solely due to transmembrane electrochromism were obtained by subtracting the small background transients measured in the presence of the potent ionophore gramicidin A (Sigma, 0.5 µM; Scho ¨nknecht et al, 1992) from the transients measured in the absence of gramicidin under otherwise unchanged conditions. The activity of PSI [monitored at 700 nm (Schaffernicht & Junge, 1982;not shown)] was less than 5% on the first flash and negligible from then on due to the presence of 200 µM DCBQ plus 2 mM hexacyanoferrate-(III) as electron acceptors.…”

Section: Methodsmentioning

confidence: 99%

Electrogenicity of Electron and Proton Transfer at the Oxidizing Side of Photosystem II

Haumann

Junge

1997

Biochemistry

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The electrogenicity of electron and proton transfer at the oxidizing side of PSII was monitored by transmembrane electrochromism of carotenoids in thylakoids and, independently, by electrometry in oxygen-evolving photosystem II core particles. It yielded dielectrically weighted distances between cofactors. They were related to the one between YZox and QA- (=100%). The electron transfer from YZ to P680+ ranged over a relative distance of 15%, while the one from Mn4 to YZox ranged over less than 3.5%. The latter result placed Mn4 and YZ at about the same weighted depth in the membrane. The oxidation of cofactor X by YZox during S2 --> S3 ranged over 10%. We tentatively attributed 7% to proton transfer into the lumen and 3% to electron transfer, in line with our notion that one proton is liberated from Xox itself. This placed X at the same depth in the membrane as Mn. Proton release upon the final oxidation of water during the oxygen-evolving step S4 --> S0 revealed relative electrogenic components of 5.5% in core particles and between 10.5% (pH 7.4) and 2% (pH 6.2) in thylakoids. The former likely reflected proton transfer from bound water into the lumen and the latter to intraprotein bases that were created in the foregoing transitions. A tentative scheme for the arrangement of cofactors at the oxidizing side of photosystem II is presented.

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Section: Methodsmentioning

confidence: 99%

Electrogenicity of Electron and Proton Transfer at the Oxidizing Side of Photosystem II

Haumann

Junge

1997

Biochemistry

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“…Which of these dominates depends on the properties of the submembrane and the defect itself. The conductance of water-filled ion channels covers a wide range from several − to several hundreds of thousands of picosiemens (pS). , The conductance of the submembrane layer can be calculated from eqs and , taking into account eq and the definition of the parameter L as L = δ/ r 0 .…”

Section: Membrane Spanning Poresmentioning

confidence: 99%

Electrochemical Impedance Spectroscopy of Tethered Bilayer Membranes

2011

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The electrochemical impedance spectra (EIS) of tethered bilayer membranes (tBLMs) were analyzed, and the analytical solution for the spectral response of membranes containing natural or artificially introduced defects was derived. The analysis carried out in this work shows that the EIS features of an individual membrane defect cannot be modeled by conventional electrical elements. The primary reason for this is the complex nature of impedance of the submembrane ionic reservoir separating the phospholipid layer and the solid support. We demonstrate that its EIS response, in the case of radially symmetric defects, is described by the Hankel functions of a complex variable. Therefore, neither the impedance of the submembrane reservoir nor the total impedance of tBLMs can be modeled using the conventional elements of the equivalent electrical circuits of interfaces. There are, however, some limiting cases in which the complexity of the EIS response of the submembrane space reduces. In the high frequency limit, the EIS response of a submembrane space that surrounds the defect transforms into a response of a constant phase element (CPE) with the exponent (α) value of 0.5. The onset of this transformation is, beside other parameters, dependent on the defect size. Large-sized defects push the frequency limit lower, therefore, the EIS spectra exhibiting CPE behavior with α ≈ 0.5, can serve as a diagnostic criterion for the presence of such defects. In the low frequency limit, the response is dependent on the density of the defects, and it transforms into the capacitive impedance if the area occupied by a defect is finite. The higher the defect density, the higher the frequency edge at which the onset of the capacitive behavior is observed. Consequently, the presented analysis provides practical tools to evaluate the defect density in tBLMs, which could be utilized in tBLM-based biosensor applications. Alternatively, if the parameters of the defects, e.g., ion channels, such as the diameter and the conductance are known, the EIS data analysis provides a possibility to estimate other physical parameters of the system, such as thickness of the submembrane reservoir and its conductance. Finally, current analysis demonstrates a possibility to discriminate between the situations, in which the membrane defects are evenly distributed or clustered on the surface of tBLMs. Such sensitivity of EIS could be used for elucidation of the mechanisms of interaction between the proteins and the membranes.

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“…Although there is strong evidence of double-helical dimers in membranes in the literature, we should also consider the possibility of a free monomer state existing in the gel phase of DPPC membrane (see Appendix). In consideration of this latter possibility we note that dimerization constants for GA were measured in DOPC (Bamberg and Läuger, 1973) and glyceroester membranes (Veatch et al, 1975), thylakoid membranes (Schönknecht et al, 1992), and 1,2-diphytanoylsn-glycero-3-phosphocholine (DPhPC) (Rokitskaya et al, 1996). The dimerization constant for DOPC in the L a phase at 25°C was reported in the range 2 3 10 13 to 10 14 mol ÿ1 cm 2 (Bamberg and Läuger, 1973;Veatch et al, 1975), depending on the method used.…”

Section: Direct Observation Of Dimer Formation By Dqcmentioning

confidence: 99%

“…On the other hand, much lower GA concentrations are needed to observe non-interacting single channels and to relate the results to energetic measurements or molecular dynamics simulations. The measurements of transmembrane electrical potential, for example, are done at nanomolar concentrations of GA (Schönknecht et al, 1992) to ensure that each channel becomes an isolated entity. A theoretical analysis shows (Nielsen et al, 1998) that in addition to 20 molecules of the boundary, the channel-induced bilayer perturbation involves 50-100 molecules.…”

Section: Introductionmentioning

confidence: 99%

Spin-Labeled Gramicidin A: Channel Formation and Dissociation

Dzikovski

Borbat

Freed

2004

Biophysical Journal

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Gramicidin A was studied by continuous wave electron spin resonance (CW-ESR) and by double-quantum coherence electron spin resonance (DQC-ESR) in several lipid membranes (using samples that were macroscopically aligned by isopotential spin-dry ultracentrifugation) and vesicles. As a reporter group, the nitroxide spin-label was attached at the C-terminus yielding the spin-labeled product (GAsl). ESR spectra of aligned membranes containing GAsl show strong orientation dependence. In DPPC and DSPC membranes at room temperature the spectral shape is consistent with high ordering, which, in conjunction with the observed high polarity of the environment of the nitroxide, is interpreted in terms of the nitroxide moiety being close to the membrane surface. In contrast, spectra of GAsl in DMPC membranes indicate deeper embedding and tilt of the NO group. The GAsl spectrum in the DPPC membrane at 35 degrees C (the gel to Pbeta phase transition) exhibits sharp changes, and above this temperature becomes similar to that of DMPC. The dipolar spectrum from DQC-ESR clearly indicates the presence of pairs in DMPC membranes. This is not the case for DPPC, rapidly frozen from the gel phase; however, there are hints of aggregation. The interspin distance in the pairs is 30.9 A, in good agreement with estimates for the head-to-head GAsl dimer (the channel-forming conformation), which matches the hydrophobic thickness of the DMPC bilayer. Both DPPC and DSPC, apparently as a result of hydrophobic mismatch between the dimer length and bilayer thickness, do not favor the channel formation in the gel phase. In the Pbeta and Lalpha phases of DPPC (above 35 degrees C) the channel dimer forms, as evidenced by the DQC-ESR dipolar spectrum after rapid freezing. It is associated with a lateral expansion of lipid molecules and a concomitant decrease in bilayer thickness, which reduces the hydrophobic mismatch. A comparison with studies of dimer formation by other physical techniques indicates the desirability of using low concentrations of GA (approximately 0.4-1 mol %) accessible to the ESR methods employed in the study, since this yields non-interacting dimer channels.

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Dimerization constant and single-channel conductance of Gramicidin in thylakoid membranes

Cited by 15 publications

References 22 publications

Electrogenicity of Electron and Proton Transfer at the Oxidizing Side of Photosystem II

Electrogenicity of Electron and Proton Transfer at the Oxidizing Side of Photosystem II

Electrochemical Impedance Spectroscopy of Tethered Bilayer Membranes

Spin-Labeled Gramicidin A: Channel Formation and Dissociation

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