Abstract: The invention relates to proton-translocating retinal proteins which exhibit a photocycle which is retarded as compared with the wild type and whose all-trans retinal contents in the light-adapted and dark-adapted states do not differ from each other by more than 10%. The invention furthermore relates to a photochromic composition and to the use of the proton-translocating retinal proteins and the photochromic composition.

Abstract: Compositions of bacteriorhodopsin variants with increased memory time and their use for reversible optical information recording are disclosed. The compositions are characterized in that the configuration of the retinal of the photoproduct is different from the configuration of the retinal of the initial state and other than 13-cis; the pH value of the composition lies between 3 and 11; the water content of the composition lies between 1 and 30% by weight with respect to the total weight of the composition; and additives for modulating the proton mobility are present in a concentration between 1 and 80% by weight of the mass of purple membrane composition used, and if required matrix materials in a concentration of up to 10% by weight with respect to the total weight of the composition are present. These compositions may be used in reversible information recording systems.