Nonlinear Effects of Periodic Electric Fields on Membrane Proteins

Abstract

The nonlinear response of a two-state chemical reaction to an oscillating electric field is described. An interesting example is a conformational transition of a membrane protein in an applied ac electric field. Even a modest external field leads to a very large local field within the membrane and hence gives rise to nonlinear behavior. The applied ac field causes harmonics in the polarization and can cause a dc shift in the state occupancy, both of which can be observed and used to determine kinetic parameters. Fourier coefficients are given for the enzyme state probability in the ac field, exactly for infinite frequency, and in a series of powers of the field for finite frequency. The results are extended to the spherical symmetry relevant to suspensions of spherical cells or vesicles.