Abstract
Two isomers isolated from irradiated all- trans-3-dehydroretinal were coupled with opsin to form visual pigment analogues. These pigments showed λ max at 517 nm (3-dehydrorhodopsin) and 500 nm (3-dehydroisorhodopsin), respectively. In the case of 5,6-epoxy-3-dehydroretinal also, two isomers were isolated and coupled with opsin to form 5,6-epoxy-3-dehydrorhodopsin and 5,6-epoxy-3-dehydroisorhodopsin. These pigments showed λ max at almost the same wavelength of 465 nm. These synthetic pigments exhibited induced circular dichroism (CD) at the range 300–600 nm like rhodopsin and isorhodopsin. The magnitude of CD or the rotational strength on the α band of 5,6-epoxy-3-dehydrorhodopsin is about equal to that of rhodopsin, but that of 3-dehydrorhodopsin is larger. From the above results and those reported elsewhere, it is proposed that the optical activity of the chromophore in the visual pigment or its analogue is not induced by the preferential selection of an inherently twisted form of retinal.
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