title: Selective reaction of hydroxylamine with chromophore during the photocycle of pharaonis phoborhodopsin.
abstract: Phoborhodopsin (pR; also called sensory rhodopsin II, sRII) is a receptor of negative phototaxis of Halobacterium salinarum, and pharaonis phoborhodopsin (ppR; also pharaonis sensory rhodopsin II, psRII) is a corresponding protein of Natronobacterium pharaonis. These receptors contain retinal as a chromophore which binds to a lysine residue via Schiff base. This Schiff base can be cleaved with hydroxylamine to loose their color (bleaching). In dark, the bleaching rate of ppR was very slow whereas illumination accelerated considerably the bleaching rate. Addition of azide accelerated the decay of the M-intermediate while its formation (decay of the L-intermediate) is not affected. The bleaching rate of ppR under illumination was decreased by addition of azide. Essentially no reactivity with hydroxylamine under illumination was observed in the case of D75N mutant which lacks the M-intermediate in its photocycle. Moreover, we provided illumination by flashes to ppR in the presence of varying concentrations of azide to measure the bleaching rate per one flash. A good correlation was obtained between the rate and the mean residence time, MRT, which was calculated from flash photolysis data of the M-decay. These findings reveal that water-soluble hydroxylamine reacts selectively with the M-intermediate and its implication was discussed.
authors.affiliation: Laboratory of Biophysical Chemistry, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo 060-0812, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Iwamoto
authors.forename: Y
authors.initials: Y
authors.lastname: Sudo
authors.forename: K
authors.initials: K
authors.lastname: Shimono
authors.forename: N
authors.initials: N
authors.lastname: Kamo
mesh_terms: D019843:Archaeal Proteins; D001436:Bacteriorhodopsins / Q000737:chemistry*; D001665:Binding Sites; D002338:Carotenoids; D025602:Halorhodopsins; D019811:Hydroxylamine / Q000737:chemistry*; D008027:Light; D010777:Photochemistry; D025603:Sensory Rhodopsins; D013329:Structure-Activity Relationship
chemical_list: D019843:Archaeal Proteins; D025602:Halorhodopsins; D025603:Sensory Rhodopsins; C061508:sensory rhodopsin II protein, archaeal; D019811:Hydroxylamine; D002338:Carotenoids; D001436:Bacteriorhodopsins