INTRAMEMBRANE ELECTRIC-FIELDS - A SINGLE CHARGE, PROTEIN ALPHA-HELIX, PHOTOSYNTHETIC REACTION CENTER

The electrode fields created by dipoles of the peptide bonds of α-helices of membrane proteins are the subject of this paper. A solution for the electrostatic potential of a point charge in a three-layer membrane model has been obtained and the values of the surface charges at the membrane/solution interface induced by this point charge have been found. The electric fields of a single α-helix have been calculated in a one-layer membrane model. It is shown that the electric field of the α-helix compensates for the loss of the Born hydration energy and promotes dissociation of the carboxyl groups located at a depth of up to 0.5 nm from the surface of water. The presence of carboxylate anions 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 considered and estimates of the electric potentials at the electron transfer chain cofactors induced by the α-helical segments of the reaction centre protein are given. It is shown that the asymmetry in the location of α-helices affects significantly the redox potentials of the electron carriers and may lead to a kinetic advantage of the A-chain of electron transfer over the B-chain. © 1990.