Orientation of membrane fragments by electric field.

Purple membrane fragments (PM) from Halobacterium halobium were oriented by a static electric field in water suspension. It was found that an electric field of approximately 20 V/cm is sufficient to achieve practically complete orientation; the PM-s have permanent electric dipole moment of (6 +/- 1) x 10(-23) Cm, the orientation of the retinal transition moment relative to the normal of the PM plane theta is (59 +/- 1) degrees, and the PM 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 orients the PM-s, too.