Conformation and Mobility of Membrane Proteins in Electric Fields

Abstract

Electric fields affect the movement and the conformation of membrane proteins and channel forming polypeptides in the membrane. Diffu sion potentials, created by a potassium concentration gradient across the membrane in the presence of valinomycin, affect the circular dichroism (CD) of bacteriorhodopsin reconstituted in lipid vesicles. The changes in CD indicate that the applied electric field, irrespective of its direction, decreases the helical fraction and increases the frac tions of the random and β structures. Donnan potentials, created across the vesicular bilayer membrane by polyelectrolytes, are used to induce the conformational changes in alamethicin. The induced change of CD by the electric field across the membrane was not symmetrical with respect to the field direction. Tangential electric fields induce lateral movements of membrane components. The eletrophoretic move ment of photosystem I (PSI) along the membrane of hypotonically swollen thylakoid vesicles induced by low electric fields (40-80 V/cm) is studied by analyzing its electrophotoluminescence (EPL) from the different poles of the vesicle. The average apparent electric mobility, determined from the time course of the increase of EPL on the enriched hemisphere and of the decrease of EPL on the depleted hemisphere, was of the order of 3.10-5 cm 2 /(V s). The distribution of PSI reaches a steady state when the diffusional, electrostatic, and other counteracting forces balance the electrophoretic driving force. The electrophoretic mobility obtained from the steady state conditions 0065-2393/94/0235-0107$08.54/0

Electroendocytosis: Exposure of Cells to Pulsed Low Electric Fields Enhances Adsorption and Uptake of Macromolecules

“…where E u will induce electrophoretic mobility toward the anodic or cathodic sides of the cell, either by direct electrophoretic mobility of the negatively charged components or by electroosmosis, respectively (McLaughlin and Poo, 1981). Though most studies of lateral electrophoretic segregation of charged membrane components have been carried out on adherent cells employing low DC electric fields (e.g., Poo, 1981;Wang et al, 2003), it was shown that a similar segregation phenomenon could be induced in photosynthetic membrane vesicles of a size comparable to that of cells (Brumfeld et al, 1989;Miller et al, 1994), when exposed in suspension to a train of unipolar pulsed electric fields of duration much shorter than the rotational time of the vesicles. Under these conditions the membrane vesicle can be considered to be in a rotational stationary state, at which time the lateral electrophoretic displacement takes place.…”