Kinetics of the fast electric signal from oriented purple membrane.

The photoinduced electric response of oriented purple membranes associated with processes before the K-intermediate decay of bacteriorhodopsin was measured in the 180-300 K temperature range. These response signals consist of two kinetically distinct components (both temperature dependent). The experimental data show a correlation between the time constants of the rise of the signal and solution resistance. A model is proposed to assign these components to two diffusion-limited processes of charge displacement in the solution. The displacement is caused by the electric field of the photoinduced transient dipole which is formed in the primary act of the bacteriorhodopsin photocycle. The two processes are assigned as: (a) the conduction of electrical current through H-bonds (time resolved only in the temperature range 180-200 K) and (b) the diffusion of charges through the interfacial layer.