Effect of single-site mutation at Asp38 of bacteriorhodopsin on the electric dipole moments of purple membranes

The effect of single amino acid substitution and membrane bound cations on the orientational behavior of purple membrane fragments was studied by elec tric light scattering. A direct experimental evidence for the contribution of the surface-exposed Asp38 amino acid residue of bacteriorhodopsin to the membrane electric dipole moments is presented. The strong drop of the perm anent electric dipole moment upon deionization of wild type bR and D38R mut ant indicates the cation binding sites location on the extracellular membra ne surface. (C) 1999 Elsevier Science B.V. All rights reserved.