title: Photoreaction cycle of phoborhodopsin studied by low-temperature spectrophotometry.
abstract: The photochemical and subsequent thermal reactions of phoborhodopsin (pR490), which mediates the negative phototaxis (phobic reaction) of Halobacterium halobium, were investigated by low-temperature spectrophotometry. At room temperature, the absorption spectrum of pR490 displayed vibrational structure with a maximum at 490 nm and a shoulder at 460 nm, which were remarkably sharpened by cooling, resulting in the appearance of two well-separated peaks. On irradiation of pR490 at -170 degrees C, a photo-steady-state mixture composed of pR490 and two photoproducts, P520 and P480, was formed. P480 had an absorption maximum at 480 nm and thermally converted to pR490 above -160 degrees C, while P520 had an absorption maximum at 515 nm and thermally converted to P350, the next intermediate, above -60 degrees C. Above -30 degrees C, P350 was converted to P530, and then reverted to pR490. P520, P350, and P530 may correspond to K, M, and O intermediates of bacteriorhodopsin, respectively, on the basis of their absorption spectra, but the intermediates corresponding to L and N intermediates were not observed. On the basis of these results, a new scheme of the photoreaction cycle of pR490 was presented.
authors.affiliation: Department of Biophysics, Faculty of Science, Kyoto University, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Imamoto
authors.forename: Y
authors.initials: Y
authors.lastname: Shichida
authors.forename: T
authors.initials: T
authors.lastname: Yoshizawa
authors.forename: H
authors.initials: H
authors.lastname: Tomioka
authors.forename: T
authors.initials: T
authors.lastname: Takahashi
authors.forename: K
authors.initials: K
authors.lastname: Fujikawa
authors.forename: N
authors.initials: N
authors.lastname: Kamo
authors.forename: Y
authors.initials: Y
authors.lastname: Kobatake
mesh_terms: D019843:Archaeal Proteins; D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000378:metabolism; D002338:Carotenoids; D005136:Eye Proteins; D005990:Glycerol; D006217:Halobacterium / Q000502:physiology*; D025602:Halorhodopsins; D008566:Membranes / Q000378:metabolism; D009154:Mutation; D010777:Photochemistry; D017299:Rod Opsins; D025603:Sensory Rhodopsins; D013053:Spectrophotometry; D013696:Temperature
chemical_list: D019843:Archaeal Proteins; D005136:Eye Proteins; D025602:Halorhodopsins; D017299:Rod Opsins; D025603:Sensory Rhodopsins; C061508:sensory rhodopsin II protein, archaeal; D002338:Carotenoids; D001436:Bacteriorhodopsins; D005990:Glycerol