Orientation of membrane fragments by electric field.

Purple membrane framents from Halobacterium halobium were oriented by a static electric field in a water suspension. It was found that an electric field of approx. 20 V/cm is sufficient to achieve practically complete orientation; the purple membranes have a permanent electric dipole moment of (6 +/- 1) . 10(-23) C . m, the orientation of the retinal transition moment relative to the direction of the electric dipole moment, theta, is (59 +/- 1)0, and the purple membrane rotational diffusion constant Drot = 0.65 s-1. It was found that because of the electrophoretic movement of the particles a hydrodynamic velocity gradient builds up which also orients the purple membranes.