title: Illumination accelerates the decay of the O-intermediate of pharaonis phoborhodopsin (sensory rhodopsin II).
abstract: pharaonis phoborhodopsin (ppR, also called pharaonis sensory rhodopsin II [psRII]) is a member of the archaeal rhodopsin family and acts as a repellent phototaxis receptor of Natronobacterium pharaonis. Upon illumination, ppR is excited and undergoes a linear cyclic photoreaction, namely, a photocycle that constitutes photointermediates such as M- and O-intermediates (ppRM and ppRO, respectively). Under a constant background illumination (>600 nm) that irradiates ppRO, the decay rate of the flash-induced ppRO increased with an increase in the background light intensity, indicating the photoreactivity of ppRO. Azide did not influence the light-accelerated ppRO decay, but the time required for the cycle to be completed became shortened in an azide concentration-dependent manner because of acceleration of ppRM decay. Hence, the turnover rate of photocycling increased appreciably in the presence of both the background illumination and the azide. The observation reported previously (Schmies, G. et al. 2000, Biophys. J. 78:967-976) is discussed in connection with the present observations.
authors.affiliation: Laboratory of Biophysical Chemistry, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Iwamoto
authors.forename: Yuki
authors.initials: Y
authors.lastname: Sudo
authors.forename: Kazumi
authors.initials: K
authors.lastname: Shimono
authors.forename: Naoki
authors.initials: N
authors.lastname: Kamo
mesh_terms: D019843:Archaeal Proteins / Q000378:metabolism*; D002338:Carotenoids / Q000378:metabolism*; D025602:Halorhodopsins; D006868:Hydrolysis; D007700:Kinetics; D019633:Natronobacterium / Q000378:metabolism / Q000528:radiation effects*; D025603:Sensory Rhodopsins; D013057:Spectrum Analysis
chemical_list: D019843:Archaeal Proteins; D025602:Halorhodopsins; D025603:Sensory Rhodopsins; C061508:sensory rhodopsin II protein, archaeal; D002338:Carotenoids