Fast electric response signals in the bacteriorhodopsin photocycle

The time behavior of flash-induced charge movements during the first steps in the bacteriorhodopsin photocycle was measured on a suspension of purple membranes oriented by an electric field. The experiments were done in the temperature range 80–278 K. During the formation of the intermediate K, two negative (with respect to the direction of the proton pump) components of the response signal are well resolved with time constants τ₁ < 3 μs and $\text{τ}{}_2\text{? 150 μ}\text{s}$ at 200 K. The distances of the charge displacements responsible for the electric signals are estimated. On the basis of the results the two components are assigned to two steps in the trans-cis isomerization of the retinal. A third negative component appears at higher temperatures which is related by time constant measurements to the K → L transition.