Picosecond Time-Resolved Resonance Raman Spectroscopy of Bacteriorhodopsin Intermediates

Abstract

The value of bacteriorhodopsin (BR) as a model for the molecular dynamics associated with the retinal chromophore in visual pigments and for the associated proton and ion pumping mechanisms across membranes has been described extensively [1–3]. Although many aspects of both the BR dynamics and the structures of BR intermediates have been reported [2–3], significant parts of the molecular mechanism underlying its biochemical function remain either unknown or only partially characterized. One such area encompasses the initial molecular changes that occur upon radiative excitation of BR. This initial phase of the “BR photocycle” is followed by a complex series of interdependent changes in molecular bonding, conformation, and environment of both the retinal chromophore and the opsin. These changes drive proton pumping across the bacterial membrane, the function which underlies the biochemical activity of BR [1–3]. Since the chemical energy for this series of processes is thought to derive from these initial steps, an understanding of the specific molecular changes is of considerable importance.