Electrical demonstration of rapid light-induced conformational changes in bacteriorhodopsin

Abstract

BACTERIORHODOPSIN (a purple pigment) is a light-driven proton pump1,2, found in patches of the cell membrane of Halo-bacterium halobium3,4, and is chemically similar to the visual pigment rhodopsin of animal eyes4. In both molecules the chromophore retinal is linked as a protonated Schiff base to a lysine residue of the apoprotein opsin1,5,6. Light induces bacteriorhodopsin to move protons from the inside to the outside of the cell. The resulting electrochemical proton gradient across the membrane is finally used to synthesise ATP. We report here the application of a new technique for the direct measurement of small capacitative charge displacements in oriented molecules. Our photoelectric measurements using asymmetrically aligned bacteriorhodopsin demonstrate that this protein undergoes reversible conformational changes after absorption of light.