Long-Lived Conformation Changes Induced by Electric Impulses in Biopolymers

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 $sec) 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.The initial step in the recording of biological memory is probably a physical, and not a biochemical, process (1, 2). A plausible mechanism for physical memory imprinting in living organisms is based on conformational transitions of metastable macromolecules or of macromolecular organizations, such as membranes (2, 3). Since metastabilities can lead to hysteresis, and because hysteresis loops were observed in several biopolymers (2, 4-6), these polymers could be possible matrices for a memory imprint. Such matrices should be able to record the electric impulses that are the information signals of the nervous system. Thus, we determined whether electric impulses can cause long-lived conformational changes in biopolymers. On physicochemical grounds, such long-lived changes are expected in domain structures capable of developing metastable states. Here, we report that electric impulses of about 20 kV/cm, and of a duration of a few Asec, do indeed induce long-lived conformational transitions in macromolecular complexes of polynucleotides (7), analyze this impulse effect, and suggest an explanation in terms of the physical chemistry of polyelectrolytes.The polynucleotides investigated consist of polyriboadenylate, poly(A), and polyribouridylate, poly(U), mixed in the molar ratio 1: 2 in aqueous NaCl solution. At sufficiently high salt concentration and neutral pH, these polymers form a three-stranded helical complex, poly(A) -2 poly(U). The basepairing scheme of this complex (8, 9) is depicted in Fig. 1. The complex polyA-2 poly(U) can develop metastability, which underlies the time-independent hysteresis loops observed in potentiometric and spectrophotometric acid-base titrations (10). Such a hysteresis cycle is shown in Fig. 2 . This barrier, which is mainly electrostatic, is strengthened by the mutual repulsion of the poly(A) -2 poly(U) triple helixes arising from the high density of negatively charged phosphates along these multistranded molecules (10). When the pH is lowered, the extent of protonation is increased. This further loosens the triple helix, lowering the nucleation barrier. Therefore, around pH'm (see Fig. 2) the "transc...

Chemical electric field effects in biological macromolecules

“…Dielectric measurements have shown that polypeptides in viscous organic solvents may undergo intramolecular helix-coil transitions in the presence of electric fields (Schwarz and Seelig, 1968). In the meantime there are many reports on fieldinduced conformational chanoes in multi-stranded as well as in single-stranded polyelectrolytes (Neumann and Katchalsky, 1972;Neumann, 1973;Kikuchi andYoshioka, 1973, 1976;Yasunaga et al, 1973;Revzin and Neumann, 1974;Prrschke, 1974Prrschke, , 1976Prrschke, , 1985.…”

Permeability changes induced by electric impulses in vesicular membranes

“…In such systems the electric impulse is capable of shifting the ionic atmosphere relative to the associated polyanions. The displacement of the screening counterions causes increased electrostatic repulsion between the polyanions and leads to partial complex dissociation (Neumann & Katchalsky, 1972).…”

A Molecular Model of Action Potentials

“…1 The amount of AcCh in the storage form is then given by the following expression: d(AcChs)/dt = Tm-'(AcChp) -rl-'(AcChs) [10] while that bound to the receptor is: d(AcChf)/dt = -r2-'(AcChf) + rl-'(AcChl) [11] Moreover, the rate of liberation of (AcChs) and (Caf) from their bound form are field-dependent because of the existence of the nonvanishing dipole moment, characteristic of the conformation of the storage proteins. In other words, the time constants 7, 7r, and 72 are written: [12] 7 = T' exp(-AKE/RT) for calcium ions, sT = rl' exp(-,usE/RT) for acetylcholine, and 72 = 72' exp(-MRE/RT) [13] for the dissociation of AcCh from its receptor, where lK is the Evolution of V, gNa, and gx.…”