Threshold effects observed in conformation changes induced by electric fields.
01 Oct 1976-Biopolymers (Wiley Subscription Services, Inc., A Wiley Company)-Vol. 15, Iss: 10, pp 1917-1928
TL;DR: In this paper, it was demonstrated that the single-strand helix-coil transition in poly(A, poly(dA), and poly(C) can be induced by application of high electric fields.
Abstract: Single-stranded polynucleotides are used as model systems for the investigation of conformational changes induced by electric fields. It is demonstrated that the single-strand helix–coil transition in poly(A), poly(dA), and poly(C) can be induced by application of high electric fields. The transition is measured by UV absorbance using polarized light at an angle of 54.8° with respect to the vector of the electric field and by electrodichroism. A linear increase of the absorbance, reflecting the helix-to-coil transition, is observed at increasing field strength. When ions are added to the polymer, electric fields do not induce conformation changes, unless a threshold value of the electric field strength E0 is exceeded. At field strengths above this threshold, the degree of transition is a linear function of the increase in field strength. The threshold values E0 show a linear increase with the logarithm of the ion concentration. Bivalent ions cause thresholds at much lower ion concentrations than mo-novalent ions. The shielding efficiency of ions is correlated to the binding affinity of these ions to the polymer.
The conformation changes induced by the field and the existence of thresholds can be explained on the basis of dissociation field effects. Similar threshold effects may be expected for other macromolecules as well as for membrane structures and may be important in the regulation of bioelectricity.
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TL;DR: An analogous situation existed in the field of protein chemistry during the period after the formulation and confirmation of the Debye—Huckel theory of ionic solutions but before Scatchard's incorporation of the theory into his analysis of the binding properties of proteins.
Abstract: Although the importance of the polyelectrolyte character of DNA has been recognized for some time (Felsenfeld & Miles 1967), few of the implications have been explored, primarily because of a lag in translating the breakthroughs in polyelectrolyte theory of the last decade into a form that is well adapted to the analysis of the specialized problems of biophysical chemistry. Perhaps an analogous situation existed in the field of protein chemistry during the period after the formulation and confirmation of the Debye—Huckel theory of ionic solutions but before Scatchard's incorporation of the theory into his analysis of the binding properties of proteins. An achievement for polynucleotide solutions parallel to Scatchard's was recently presented by Record, Lohman, & de Haseth (1976) and further developed and reviewed by Record, Anderson & Lohman (1978).
2,686 citations
TL;DR: Reactions in Polar Media and Polyionic Macromolecules: Permanent and Induced Dipole Moments in Polyionics.
Abstract: VI. REACTION MoMErcr AND ELECTRIc-CI~-.MICAL MECHANISM 1. Reaction Moments from Dielectric Data 2. Permanent and Induced Dipole Moments (a) Individual dipole moments (b) Total polarization (i) Induced moment (ii) Permanent moment (c) Form factors and g-factors 3. Reaction Moment and Equilibrium Constant (a) Non-polar polarizable spheres (b) Polar non-polarizable spheres (c) Polar polarizable spheres (Onsaqer) 4. Reactions in Polar Media (a) Kirkwood-FrShlich equation (b) Ion-pair equilibria in aqueous solution 5. Induced Dipole Moments in Polyionic Macromolecules
68 citations
TL;DR: It is demonstrated that the isotropic absorption and linear dichroism in an unknown flow field can be used to determine base tilt in polynucleotides if three transitions are measured and the directions of the corresponding dipoles are known.
Abstract: We demonstrate that the isotropic absorption and linear dichroism in an unknown flow field can be used to determine base tilt in polynucleotides if three transitions are measured and the directions of the corresponding dipoles are known. The method is applied here to reach conclusions about the base tilt in poly(rA), poly(rA)+·poly(rA), and poly(rC). The respective values are: 28° tilt about the axis + 50° toward C8 from the C1′ N9, and 25° tilt about the axis + 118° toward C5 from C1′ N1. The results for poly(rA)+·poly(rA) are consistent with the accepted model. Spectra were measured for poly(rC)+·poly(rC), but definite conclusions must await reliable directions for transition dipoles. The dipole direction for the 218-nm transition in rC is found to be +13° or +43° toward C5 from C1′ N1. The CD spectra to about 168 nm are presented and discussed.
32 citations
TL;DR: The threshold effect found experimentally by Pörschke, and particularly the observed linear dependence of the threshold field on the logarithm of the ionic strength, appears here as a simple consequence of the linear increase of the stabilization free energy with the logarym of Ionic strength.
26 citations
TL;DR: It is shown that increasing the applied field causes denaturation-like transition of the enzyme at a current power which does not induce excessive Joule heating in the capillary.
23 citations
References
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TL;DR: In this article, the effect of an external electric field on the electrolytic dissociation is computed kinetically from the equations for Brownian motion in the combined Coulomb and external fields, and the result is an increase of the dissociation constant, by the factor K(X)/K(0) = F(b) = 1+b+(1/3)b2.
Abstract: The effect of an external electric field on the electrolytic dissociation is computed kinetically from the equations for Brownian motion in the combined Coulomb and external fields. The result is an increase of the dissociation constant, by the factor K(X)/K(0) = F(b) = 1+b+(1/3)b2..., where the parameter b is proportional to the absolute value of the field intensity, and inversely proportional to the dielectric constant. In water at 25°, F(b) = F(1) = 2.395 for a field of 723 kilovolt/cm, while in benzene, the same increase of the dissociation constant is obtained for a field of only 21 kilovolt/cm. The theory is quantitatively confirmed by the deviations from Ohm's law which have been observed for solutions of weak electrolytics in water and in benzene. For solutions of salts in acetone, and for solid electrolytes such as glass, mica, celluloid, etc., the observed increments of conductance are smaller than those expected from the theory, but still of the predicted type and order of magnitude. The kineti...
1,067 citations
381 citations
TL;DR: The results give first experimental evidence for three effects of major significance: the system exhibits dielectric relaxation due to a chemical rate process, there is a considerable electric field effect of the helix–coil transition and conformation changes in biological systems could be potentially caused by direct action of an electric field.
Abstract: Dielectric relaxation of poly(γ-benzyl L-glutamate) in solution has been studied in the 5 kcps-10 Mcps range for various values of the helix content. The results give first experimental evidence for three effects of major significance. (1) The system exhibits dielectric relaxation due to a chemical rate process (namely helix formation). This confirms recent theoretical predictions. (2) The mean relaxation time τ* of the helix–coil transition could be evaluated as a function of the degree of transition. The results are in excellent agreement with a previously developed theory. At the midpoint of transition it is found τ*max = 5 × 10−7 sec. The elementary process of helical growth turns out to be practically diffusion-controlled (with a rate constant of hydrogen bond formation of 1.3 × 1010 sec−1). (3) There is a considerable electric field effect of the helix–coil transition. This indicates that conformation changes in biological systems could be potentially caused by direct action of an electric field.
133 citations
TL;DR: A polarization mechanism is proposed to explain the structural transitions observed in the biopolymers exposed to the impulses, and the significance of the impulse experiments with regard to the question of biological memory recording is briefly discussed.
Abstract: Electric impulses are capable of inducing long-lived conformational changes in (metastable) biopolymers. Results of experiments with poly(A)·2 poly(U) and ribosomal RNA, which are known to develop metastabilities, are reported. A polarization mechanism is proposed to explain the structural transitions observed in the biopolymers exposed to the impulses. In accordance with this idea, the applied electric field (of about 20 kV/cm and decaying exponentially, with a decay time of about 10 μsec) induces large dipole moments by shifting the ionic atmosphere of multistranded polynucleotide helices. This shift, in turn, causes strand repulsion and partial unwinding. The fields used in our experiments are of the same order of magnitude as those in nerve impulses. The significance of the impulse experiments with regard to the question of biological memory recording is briefly discussed.
108 citations