Internal Electric Fields Generated by Surface Charges and Induced by Visible Light in Bacteriorhodopsin Membranes. (Reannouncement with New Availability Information).

摘要

Bacteriorhodopsin functions as a light driven proton pump, and is the major protein component in the purple membrane of Halobacterium halobium. An externally applied electric field has a prominent effect on its photocycle kinetics. While the purple membrane has highly asymmetrical negative surface charges, the effect of varying ionic strengths on the photocycle kinetics is rather modest. The present paper deals with this paradox by invoking a simple mechanistic model of two coupled interfacial photoreactions along with two additional refined models. The internal electric fields arising from fixed surface charges and from surface charges induced by visible light (400-700 nm) are analyzed with regard to their interaction as well as the interaction between the endogenous (surface potentials generated by fixed and light-induced surface charges) and the exogenous (externally applied potential and/or diffusion potential electric field). It is possible that bacteriorhodopsin as an electro-sensitive element responds to the local voltage gradient (internal electric field) rather than to the voltage level.