Abstract

Bacteriorhodopsin (BR) is a protein found in the purple membrane of the salt-loving bacterium, Halobacterium Salinarium. One of the unique properties of this material is a light-driven proton pumping process and the associated photocycle that enables the bacterium to convert light energy into chemical energy if the ambient oxygen level becomes too low for respiration [1]. The photocycle involves a number of intermediate states characterised by different lifetimes and different absorption spectra. There is just one deprotonised state in the photocycle; known as the M-state, it is the most stable of the photocycle intermediates and as a result of the deprotonisation its absorption spectrum is significantly blue-shifted from that of the ground (B) state [1]. The lifetime of the M-state is the order of 10 ms for aqueous BR solutions and the absorption peak wavelength is shifted from the original position of 568 nm for the B-state, to 412 nm.

© 1996 Optical Society of America