pH-dependence of electric light scattering by water suspension of purple membranes

The electro-optical behaviour of purple membranes (PM) water suspension in pH range 3.3–6.2 was studied by electric light scattering method. At low degree of orientation the steady-state electro-optical effect (EOE) increases in pH range 3.8–5.6, but an abnormal behaviour of the pH-dependence is observed outside this range. At full orientation EOE has two peaks at pH 3.6 and 5.8, related to changes in membrane geometry. Relaxation time increases in pH range 3.9–5.5, which corresponds to membrane area increase with ≈20%. The resonance character of pH-dependence around the peaks was explained by reversible alterations in PM curvature, related to asymmetrical increase of the area of both membrane surfaces.