(5‐demethyl)‐Bacteriorhodopsin analogue: its formation and light‐driven proton pump action

The binding of the isomers (all‐trans, 13‐cis, 11‐cis and 9‐cis) of 5‐demethylretinal to bacterioopsin and the light—dark adaptation as well as the light‐driven proton pump action of the resulting bacteriorhodopsin analogue were studied. The (5‐demethyl)‐bacteriorhodopsinis formed ≈ 3‐times faster than unmodified bacteriorhodopsin and shows an efficient light‐driven proton pump action. These findings show that upon binding of retinal to bacterioopsin the protein forces the chromophore to adopt a more planar ring‐chain conformation than in free retinal.