ELECTRIC-FIELD AND PHOTOCHEMICAL EFFECTS IN D85N MUTANT BACTERIORHODOPSIN SUBSTITUTED WITH 4-KETO-RETINAL

All-trans 4-keto-retinal has been incorporated into bleached apomembra nes of D85N mutant bacteriorhodopsin. The resulting pigment exhibits a pH-dependent equilibrium between forms with a protonated (pink) and a n unprotonated (yellow) Schiff base, with pK = 6.15. Optical absorptio n changes produced by flash illumination of suspensions of the protona ted and unprotonated forms have been recorded. Applying an electric fi eld across a thin, dry film of the pink form of the pigment produces s pectral changes characteristic of Schiff-base deprotonation. These exp eriments demonstrate that electric-field-induced Schiff-base deprotona tion, first discovered in blue D85N bacteriorhodopsin, can be the basi s of electrochromic materials of different colors made using retinal-a nalog substitution as well as genetic mutation. (C) 1997 Elsevier Scie nce S.A.