[Electrical fields in membrane proteins]

The electric fields created by dipoles of the peptide bonds of alpha-helices of membrane proteins are considered. It has been shown that the electric field of the alpha-helix compensates for the loss of the Born hydration energy and promotes dissociation of the carboxyl groups located at the depth of up to 5 A from the water surface. The presence of the carboxylate anion facilitates penetration of the hydronium ion into the membrane and lowers the potential barrier by 0.1-0.2 eV (depending on the membrane thickness). A three-layer model of the reaction centre of photosynthetic bacteria is proposed. An estimate of the dielectric constant of different parts of the reaction centre is obtained by means of comparison of photoinduced electrogenetic transmembrane potential displacement with structural data. Estimates of the electric potentials at the electron transfer chain cofactors induced by the alpha-helical segments of the reaction centre protein are given. It is shown that the asymmetry in the location of alpha-helices affects significantly the redox potentials of the electron carriers and lead to a kinetic advantage of the A-chain of electron transfer over the B-chain.