Visual purple, rhodopsin, is composed of retinal and a protein called opsin. When rhodopsin absorbs light energy, its retinal component undergoes photoisomerization accompanied by a change in conformation of opsin. This light-induced conformational change is a trigger which excites the nerve cells of the retinal rods. Recent progress in polypeptide chemistry has prompted the authors to construct a system analogous to that in the visual excitation which permits light-induced conformational changes of polypeptides. Among many polypeptides, poly- beta -alkylaspartates seem to be especially delicate in their conformations. In the reported experiments, the authors prepared some copolymer series of polypeptides containing para- or meta-phenylazo-benzyl-L-aspartate units and carried out trans-cis photoisomerization of the side-chain azobenzene groups. They report the results of a copolymer of beta -benzyl-L-aspartate and beta -p-phenylazobenzyl-L-aspartate (41:59) which has been proved to undergo both light-induced conformational change and subsequent relatxation back to the original conformation.
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