Electric field promotion of the bacteriorhodopsin BR570 to BR412 photoconversion in films of Halobacterium halobium purple membranes

The combined action of electric field (10⁵–10⁷ V · m^?1) and light (380–580 nm, 80 W · m^?2) activating the photoenergetic reaction of bacteriorhodopsin (BR) in dry films of purple membranes from Halobacterium halobium was studied. A new stimulating effect of the field on the BR₄₁₂ intermediate accumulation in the normal photochromic cycle of BR₅₇₀ has been observed. The formation of the product BR₄₁₂ is supposed to be accompanied by specific rearrangements of certain charged, polar and polarizable groups in the BR pigment-protein matrix. Such an intrinsic polarization could be promoted by an external electric field, the displacement vector of those groups being oriented in the direction of the field. The dielectric polarization properties of the purple membranes have been demonstrated by electret-thermal analysis.