Light-inducedtrans-cis isomerization of retinal by a protein from honeybee retina

Summary Two retinal-binding proteins (RBP-A and RBP-B) isolated from the honeybee retina were further purified by ion-exchange chromatography. Whereas RBP-A seems to be denatured by this procedure, RBP-B remains intact with respect to its photochemical characteristics (Fig. 3a). Analysis of the geometric isomers of retinal bound to RBP-B by high performance liquid chromatography demonstrated that all-trans retinal was the chromophore of the non-irradiated RBP-B. Irradiation converted RBP-B (_max 440 nm) into a photoproduct (_max 370 nm) the chromophore of which was 11-cis retinal, i.e., light isomerized all-trans retinal almost exclusively to the 11-cis form (Fig. 3b). Irradiation of a solution of RBP-B in the presence of excess all-trans retinal also led to the formation of 11-cis retinal indicating that RBP catalyzes the photoisomerization of all-trans retinal. The physiological significance of RBP-B is discussed with respect to the renewal of rhodopsin.Abbreviations RBP retinal-binding protein - HPLC high performance liquid chromatography