PHOTOCHEMICAL CONVERSION OF THE O-INTERMEDIATE TO 9-CIS-RETINAL-CONTAINING PRODUCTS IN BACTERIORHODOPSIN FILMS

The photochemical activity of the O-state was investigated in bacterio rhodopsin (BR) films containing wildtype BR at pH 6.5 in the presence of glycerol. The formation of a photoproduct of O with an absorption m aximum at 490 nm and 9-cis-retinal configuration was found. This 490-n m product was named P and shows a slow thermal reaction into a compoun d with a maximal absorption at 380 nm which was named Q and contains f ree 9-cis-retinal in the proteins binding site. The photoproducts of O , i.e., P and Q, are very similar, or even identical, to those previou sly observed in blue membranes. Common to the O-state and blue membran e forms of bacteriorhodopsin is a protonated aspartic acid 85, and we suggest that it is the reduced negative charge around the Schiff base which is responsible for the 9-cis photoisomerization. The release of a proton from aspartic acid 85 is linked to the conversion of the O-st ate back to the initial state of BR. Therefore the conditions of low p roton mobility in BR films containing glycerol favor the accumulation of the O-state. For optical and holographic applications such BR films are very attractive. It is possible to create photoproducts with red light which are thermally stable at room temperature and that can be p hotochemically erased. Dependent on the light composition both propert ies can be realized in the same sample material. This feature may brid ge the gap between information processing and short-term and long-term storage of information with BR.