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Images on a Purple Membrane

by Dr Gerold Baier
Norbert Hampp from the Institute for Physical Chemistry at the University of Munich and Alfred Miller from the Wackcr-Chemic company In Munich are successfully researching chemical Image-processing with the Bactertorhodopsln (BR) molecule, which Is closely related to the rhodopsin tn the retina of the human eye. It Is Integrated In the purple membrane of certain photosynthetically active bacteria which live in extremely saline
Before it can be analysed in the laboratory, the purple membrane needs to be dissolved out of the bacteria and embedded in a plastic foil. The BR-molecule can then exist in two chemical forms, depending on the type of light It is exposed to: if the initial, violet form Is Irradiated with green bgh- It turns yellow. This process can be reversed with blue light
For this reason, the BR Is suitable as a means of storing optical Information, depending on the type of light-used. If this can be utilised successfully aa a basis for technical applications. it will be possible to expand the memories of presentday computers by several orders of magnitude, as the individual molecules are much smaller than conventional Tilts" on magnetic tape. Moreover. whereas the memory units on magnetic tapes must be distributed strictly on one level, rhodopsin molecules can be stacked In several layers so as to save space.
Bacteriorhodopsin consists of two molecular components: light-sensitive retinal and a protein constituent. This protein Is also responsible for the function of the molecule. Alterations in Its chemical structure result in BR variations
with new characteristics — a phenomenon which researchers have been focussing on particularly.
At the Max Planck Institute for Biochemistry in Martln-srled. a team of scientist led by Professor Dieter Oesterhelt is dealing with structural changes in BR resulting from interventions tn the genotype of the bacterium. As these Interventions are not aimed al any specific result, the rhodopsin variations generated must be enriched an ascertained again with new physicochemical methods.
By combining biochemical and genetic techniques, various BR-types are obtained which.for example, react to the light of a wavelength longer than that which triggers the natural molecule's re sponse. The first devices to use a BR-foll, e g. an interferometry camera, are already being tested.
Another Interesting field involving the application of the bacieriorhodopsfn is holography. which is the art of producing three-dimensional Images of any object
For this purpose, the object is Illuminated with a laser beam, and the scattered rays are collected on light-sensitive material. The hologram thus obtained can be used to create a three-dimensional picture of the original. Using BR-foils. Hampp arid Miller have successfully recorded holograms In real time, i.e. instantaneously and without requiring any time-consuming film dc-vclopment.
In contrast to conventional photosensitive material cur rently used in photography, such as sliver halides, the BR foil can always be reused after exposure. For this reason, Il is theoretically possible to take up to 1000 shots per second at extremely high resolution
Thus, changes in the loca tlon or perspective of an object recorded holographically can be registered Immediately on BR-folls.
As all the data concerning the object Is available Instantaneously, holography is basically also suitable for the pattern recognition of complex shapes. However, thts application Is restricted by the fact that a laser must always be used as the light source.
Knowledge on the structure and operation of rhodopsin is continually being gained. As early as 1988, the German re searchers Hartmut Michel, Johann Desicnhofer and Robert Huber received the Noble Prize for Chemistry, for their explanation of the structure of a rhodopsin complex from the purple bacterium. For the last several years, research groups have worked on further potential applications, including light-operated desalination plants and the generation of power from light using the principle of bacterial photosynthesis.
— German Research Service