Photoinduced anisotropy in chemically-modified films of bacteriorhodopsin and its genetic mutants

Abstract Photoinduced anisotropic properties of bacteriorhodopsin (BR) have attracted a lot of attention in the area of optical image processing. Here we report that chemical enhancement of wild-type BR, site-specific mutants D96E and D96N BR results in significant increase of the photoanisotropic response. The use of Asp-96 genetic mutants brings about just a slight increase in anisotropy and photosensitivity as compared to the effect of chemical modification of BR. To study the enhancement mechanism, the contributions of photoinduced birefringence and dichroism are estimated in the total photoanisotropic response. It is the increase of a total number of bleached BR molecules that are converted into a shortwavelength-absorbing intermediate M upon chemical modification of BR in films that results in the photoanisotropy increase. It is shown that photoinduced birefringence has positive extremum at around 635 nm and negative extremum – at around 460 nm. Maximum photoanisotropic response is detected with orthogonal polarization of the exciting beams of He–Ne and He–Cd lasers (B-M-type of photoinduced anisotropy).