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Bacteriorhodopsin O-state Photocycle Kinetics: A Surfactant Study


*Corresponding author email: (Mostafa A. El-Sayed)


The spectroscopy and dynamics of interaction between the O intermediate of bacteriorhodopsin (bR) and several surfactants (cetrimonium bromide [CTAB], sodium dodecyl sulfate [SDS] and diethylene glycol mono-n-hexyl ether [C6E2]) were investigated using steady-state UV–VIS spectrometry, circular dichroism spectroscopy and time-resolved absorption techniques. The steady-state spectral results show that bR can retain its trimeric state without severe damage in the molar concentration ratio of C6E2/bR ranging up to 4000. Time-resolved observations indicate that the rise and decay rates and transient populations of the O state can be increased in the presence of nonionic surfactant C6E2; however, these studies indicate the opposite phenomenon in the presence of the ionic surfactants CTAB and SDS. The observed 40% enhancement in the transient population of the O intermediate state that results from treatment of C6E2 is proposed to result from an expanding bR structure, which leads to more effective proton pumping efficiency in the photosynthetic system of bR.