Patent ID: 7939220

Claim:
A photochromic composition comprising: (i) a proton-translocating retinal protein that is a mutein of a Halobacterium salinarium bacteriorhodopsin, which exhibits a retarded photocycle (type 1 mutation) and whose all-trans retinal contents in the light-adapted and dark-adapted states do not differ from each other by more than 10% (type 2 mutation), wherein said muteins comprises SEQ ID NO:1 except for one or more amino acid substitutions at a position selected from the group consisting of D38, D102, and D104 (type 1 mutation) and one or more amino acid substitutions at a position selected from the group consisting of V49, A53, L93, M118, G122, S141, and M145 (type 2 mutation); (ii) at least one additive selected from a stabilizer, a foam formation-diminishing additive, a UV light-absorbing additive and a buffering substance; and (iii) at least one additional component selected from glycerol, an organic polymer and an organic solvent.