The equivalence of fluctuation analysis and chemical relaxation measurements: a kinetic study of ion pore formation in thin lipid membranes

Zingsheim, H. P.; Neher, Erwin

doi:10.1016/0301-4622(74)80045-1

Cited by 108 publications

(53 citation statements)

References 22 publications

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“…The order of the channel-forming reaction has been further studied by a voltage-jump approach (9), which is based on the finding that the number of channels increases as the membrane is thinned by an applied voltage (6). The results of these voltage-jump experiments are consistent with the hypothesis of an equilibrium in the membrane between a nonconducting monomer and a conducting dimer of gramicidin A (9), but these data do not strongly exclude the possibility that channel formation is a trimerization (10). Similar results have also been obtained from an autocorrelation analysis of the conductance fluctuations (1 0-1 1).…”

Section: Introductionsupporting

confidence: 53%

The structure of the gramicidin A transmembrane channel

Veatch

1976

J Supramol Struct

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Gramicidin A is a linear polypeptide antibiotic that facilitates the diffusion of monovalent cations across lipid bilayer membranes by forming channels. It has been proposed that the conducting channel is a dimer which is in equilibrium with nonconducting monomers in the membrane. To directly test this model in several independent ways, we have prepared and purified a series of gramicidin C derivatives. All of these derivatives are fully active analogs of gramicidin A, and each derivative has a useful chromophore esterified to the phenolic hydroxyl of tyrosine #11.Simultaneous conductance and fluorescence measurements on planar lipid bilayer membranes containing dansyl gramicidin C yielded four conclusions: 1) A plot of the logarithm of the membrane conductance versus the logarithm of the membrane fluorescence had a slope of 2.0 * 0.3, over a concentration range for which nearly all the gramicidin was monomeric. Hence, the active channel is a dimer of the nonconducting species. 2) In a membrane in which nearly all of the gramicidin was dimeric, the number of channels was approximately equal to the number of dimers. Thus, most dimers are active channels and so it should be feasible to carry out spectroscopic studies of the conformation of the transmembrane channel.3) The association constant for dimerization is more than 1,000-fold larger in a glycerolester membrane with 26 &hydrocarbon thickness than in a 47 &glycerolester membrane. The dimerization constant in a 48 a-phosphatidyl choline membrane was 200 times larger than in a 47 &glycerolester membrane, showing that it depends on the type of lipid as well as on the thickness of the hydrocarbon core. 4) We were readily able to detect 1 O-I4 mole cmP2 of dansyl gramicidin C in a bilayer membrane, which corresponds to 60 fluorescent molecules per square pm. The fluorescent techniques described here should be sufficiently sensitive for fluorescence studies of reconstituted gates and receptors in planar bilayer membranes.An alternative method of determining the number of molecules of gramicidin in the channel is to measure the fraction of hybrid channels present in a mixture of 2 chemically different gramicidins. The single-channel conductance of p-phenylazobenzene-sulfonyl ester gramicidin C (PABS gramicidin C) was found to be 0.68 that of gramicidin A. In membranes containing a mixture of these 2 gramicidins, a hybrid channel was evident in addition to 2 pure channels. The hybrid channel conductance was 0.82 that of gramicidin A. Fluorescence energy transfer from dansyl gramicidin C to diethylamino-phenylazobenzene-sulfonyl ester gramicidin C (DPBS gramicidin C), provided an independent way to measure the fraction of hybrid channels on liposomes. For both techniques the fraction of hybrid channels was found to be 2ad where a2 and d2 were the fractions of the 2 kinds of pure channels. This result strongly supports a dimer channel and the hybrid data excludes the possibility of a William Veatch is now at the Department of Pharmacology, Harvard Medical School, Boston...

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Section: Introductionsupporting

confidence: 53%

The structure of the gramicidin A transmembrane channel

Veatch

1976

J Supramol Struct

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“…Hydrated Protein Powders Some interesting events have been detected by NMR and dielectric measurements in protein powders during the hydration process. The NMR results have been recently and extensively reviewed, 3 1 therefore only a brief summary will be reported here. The dielectric data have not yet been critically analyzed and will therefore be considered in some detail.…”

Section: S Helix-coil Transition Rates In Polypeptidesmentioning

confidence: 99%

Statistical Time Events in Enzymes: A Physical Assessmen

Careri

Fasella

Gratton

et al. 1975

CRC Critical Reviews in Biochemistry

200

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“…These results led the authors to conclude that the chemically linked gramicidin forms channels per se without further association. One may then wonder what a noise analysis would, in this particular case, lead to since previous works have shown that the power spectrum of the current fluctuations for membranes containing gramicidin A is mainly determined by the formation and disappearance of the channels, i.e., by the fluctuation in the number of dimers (Zingsheim & Neher, 1974;Kolb, L~iuger & Bamberg 1975;. Shall we expect with the chemically dimerized form of gramicidin A a Lorentzian type power spectrum (constant value at low frequencies, 1/f 2 behavior for f > fc, fc being the corner frequency) as in the case of normal gramicidin A, but with a lower corner frequency, or do we have to look for a totally different noise behavior?…”

mentioning

confidence: 98%

“…In order to determine the kinetics of the dimerization process by which gramicidin A channels are formed, previous studies have used voltage jump and noise analysis techniques (Bamberg & Liiuger, 1973Zingsheim & Neher, 1974;Kolb, L~iuger & Bamberg, 1975;Bamberg & Benz, 1976;. By applying a voltage jump across a membrane doped with gramicidin A, it is indeed possible to shift the equilibrium between nonconducting monomers and conducting dimers toward the dimers side, and thus to produce a time-dependent increase of conductance from which the kinetic parameters can be obtained.…”

mentioning

confidence: 99%

1/f noise in black lipid membranes induced by ionic channels formed by chemically dimerized gramicidin A

Sauvé

Bamberg

1978

J. Membrain Biol.

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Summary. The noise behavior of lipid bilayer membranes, doped with a chemically dimerized gramicidin A, was investigated. In contrast to normal gramicidin A, which generates a Lorentzian type power spectrum due to the formation and disappearance of conducting dimers, the current power spectrum density S m (f) obtained with this gramicidin A derivative showed over several orders of magnitude a clear 1If behavior. The intensity of this 1If component was analyzed as a function of the membrane-applied voltage, membrane resistance, electrolyte concentration, and composition. The relationship between the meansquare fluctuation in current and the membrane current mean value was found to follow Hooge's equation, i.e., 612 = ~I2/Nf where N is the number of channels and ~ is a constant equal to 1.0 x 10 -2. It is suggested that a 1If type noise was observed because the chemically dimerized form of gramicidin A produces long lasting cation selective channels.

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The equivalence of fluctuation analysis and chemical relaxation measurements: a kinetic study of ion pore formation in thin lipid membranes

Cited by 108 publications

References 22 publications

The structure of the gramicidin A transmembrane channel

The structure of the gramicidin A transmembrane channel

Statistical Time Events in Enzymes: A Physical Assessmen

1/f noise in black lipid membranes induced by ionic channels formed by chemically dimerized gramicidin A

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