Electrostriction of purple membranes and the model of active proton transfer in bacteriorhodopsin

To examine the role of the protein for the proton transfer the comparative analysis of electro-acoustic effect and the photoelectric response of dried films of purple membranes (PM) of Halobacterium salinarum is carried out. The films of different degrees of orientation of the PM's as well as oriented films after the acid treatment for different periods of time are analyzed. It is shown that characteristic values of the electric signals in both experiments, namely the critical value of the bias voltage in electro-acoustic measurements and the maximum value of the photoelectric response, are sensitive to the orientation degree of the PM's in the film under consideration. The mean value of the internal electric field of the purple membrane is determined to be 2.4 107 V/m and directed from the cytoplasmic side towards the endoplasmic side of the membrane. The changes in the photoelectric response signal at the presence of the external electric field are used to determine the photoconductivity of the stand-alone photoactive bacteriorhodopsin molecule. The model explaining the proton transfer mechanism in bacteriorhodopsin based on the experimental observations is postulated and developed.

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