MOLECULAR MECHANISM OF THE DIFFERENTIAL PHOTOELECTRIC RESPONSE OF BACTERIORHODOPSIN

In order to determine the molecular origin of the differential photocu rrent from bacteriorhodopsin (bR), the photoelectric response of br fi lm deposited on an indium tin oxide (ITO) conductive glass electrode u nder CW excitation is compared with that under pulsed laser excitation at different pH and with opposite membrane orientation with respect t o the ITO electrode surface, The characteristics (sign and magnitude) of the dominant component of the differential photocurrent (appearing on the millisecond time scale) are found to correlate with the process of proton release into, or uptake from, the aqueous solution during t he photocycle under different experimental conditions. This suggests t hat the differential current results mainly from the change in the Hconcentration at the bR-ITO electrode interface.