Piezoelectric model for active proton transport in bacteriorhodopsin

Abstract

Bacteriorhodopsin is a photoactive protein performing the transmembrane proton pumping through the purple membrane of Halobacterium salinarum. Experimental results of the electrical studies of the dried purple membrane films excited by short light pulses are presented. The time constant of the photoelectric response of the purple membrane film corresponds to the optically detectable L intermediate lifetime that is tens of micro seconds. Absence of the positive part of the photoelectric response signal in the time range of tens of microseconds under acidic conditions supports the assumption about the possibility of blockage of the proton transfer. The polarization field is a stimulating factor of the active proton transfer according to the assumption of the suggested two-state model. The mechanical-electrical properties of the dipole materials and the piezoelectric effect of the hydrogen bonds are discussed in the context of the zwitterionic state of the Schiff base and its counter ion Asp85. On the basis of the recent crystallographic data and molecular dynamics simulations it is concluded that the polarization of the Schiff base is a consequence of the mechanically strained hydrogen bonds caused by the retinal photoisomerization. The reorganized H-bond network impedes the proton way back, and the proton accomplishes work while moving in the external circuit.

Relaxation Pathways of Excited N-(Triphenylmethyl)salicylidenimine in Solutions

“…Bacteriorhodopsin is a good example demonstrating such proton transfer initiated by electronic excitation of the retinal chromophore linked to the protein via protonated Schiff base. The origin of the active proton driving force in bacteriorhodopsin remains still to be disclosed. − For this purpose the proton transfer reaction is widely considered in various model systems constituting intramolecular hydrogen bonds. Imine is a typical moiety present in molecular compounds containing the Schiff base as a functional group.…”

“…The origin of the active proton driving force in bacteriorhodopsin remains still to be disclosed. [1][2][3][4] For this purpose the proton transfer reaction is widely considered in various model systems constituting intramolecular hydrogen bonds. Imine is a typical moiety present in molecular compounds containing the Schiff base as a functional group.…”