CHARGE MOTIONS STUDIED IN THE BACTERIORHODOPSIN MUTANTS D85N AND D212N

The photoelectric response signals of the D85N and D212N bacteriorhodopsin mutants expressed in a Halobacterium halobium strain were measured. The purple membranes containing only the mutant protein were oriented and immobilized in polyacrylamide gel. The absorption changes and electric response signals were measured after laser excitation, enabling the related charge motions in the protein to be followed during the photocycle. The signals were analysed on the basis of the sequential model with reversible reactions for the photocycle of the mutants. The transition lifetimes and electrogenicity of the intermediates were determined. From this analysis the relative electrogenicity of the L intermediate was established. The results corroborate the existence of a conformational change during the photocycle in these bacteriorhodopsin mutants.