Molecular Mechanism of tR - New Photosensory Receptor in Halobacterium Halobium

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In addition to bacteriorhodopsin and halorhodopsin, third-rhodopsin like pigment (tR) was found in Halobacterium halobium. Recent Studies show sensory rhodopsin (sR; renamed from tR) is responsible for positive phototaxis by red light and for negative phototaxis by blue light. In this project characterization of sensory rhodopsin (SR590) has a long live intermediate absorbing 370 nm (SR370). Isomeric composition of retinal in sensory rhodopsin was determined by HPLC after chemical extraction.The isomeric form of retinal in SR590 and SR370 was found to be all-trans retinal and 13-cis retinal, respectively.Photocycle of sensory rhodopsin was studied using laser flash photolysis. Primary photoproduct of SR570 is SR680, absorbing 680 nm. Bogomolni et al show SR680 converts to SR370. However, we found new intermediate SRL between SR680 and SR370. As we already showed, quantum yield of SR370 decreased in decreasing temperature. In order to explain this phenomena, we studied temperature effec … More t on quantum yield of SR680. In contrast with SR370, quantum yield of SR680 is independent of temperature. These results suggest there is bypass from SR680 to SR590. SR370 is photoreceptor for negative phototaxis and is expected to have its own photocycle. After accumulate of SR370 with continuous illumination of red light, photocycle of SR370 was studied with blue pulse light. The maximum in the difference spectrum measured 1 ms after the flash is - 520 nm.Interaction between ions and sensory rhodopsin was studied by flash photolysis under high pressures. This method enable us to obtain activated molar volume changed <DELTA> <V^(++)> . Though halorhodopsin gave different volume changes with different sodium halide, volume changes of sensory rhodopsin were independent of sort of monovalent ion. However, Divalent cation ( <Mg^(++)> , <Ca^(++)> ) affect the molar volume changes.In order to characterize sensory rhodopsin, this pigment have to be isolated after solublized. This project is under investigation. Less