title: Photochemistry of Acetabularia rhodopsin II from a marine plant, Acetabularia acetabulum.
abstract: Acetabularia rhodopsins are the first microbial rhodopsins discovered in a marine plant organism, Acetabularia acetabulum. Previously, we expressed Acetabularia rhodopsin II (ARII) by a cell-free system from one of two opsin genes in A. acetabulum cDNA and showed that ARII is a light-driven proton pump [Wada, T., et al. (2011) J. Mol. Biol. 411, 986-998]. In this study, the photochemistry of ARII was examined using the flash-photolysis technique, and data were analyzed using a sequential irreversible model. Five photochemically defined intermediates (P(i)) were sufficient to simulate the data. Noticeably, both P(3) and P(4) contain an equilibrium mixture of M, N, and O. Using a transparent indium tin oxide electrode, the photoinduced proton transfer was measured over a wide pH range. Analysis of the pH-dependent proton transfer allowed estimation of the pK(a) values of some amino acid residues. The estimated values were 2.6, 5.9 (or 6.3), 8.4, 9.3, 10.5, and 11.3. These values were assigned as the pK(a) of Asp81 (Asp85(BR)) in the dark, Asp92 (Asp96(BR)) at N, Glu199 (Glu204(BR)) at M, Glu199 in the dark, an undetermined proton-releasing residue at the release, and the pH to start denaturation, respectively. Following this analysis, the proton transfer of ARII is discussed.
authors: Faculty of Life Science, Hokkaido University, Sapporo 060-0810, Japan.
authors: Takashi
authors: T
authors: Kikukawa
authors: Kazumi
authors: K
authors: Shimono
authors: Jun
authors: J
authors: Tamogami
authors: Seiji
authors: S
authors: Miyauchi
authors: So Young
authors: SY
authors: Kim
authors: Tomomi
authors: T
authors: Kimura-Someya
authors: Mikako
authors: M
authors: Shirouzu
authors: Kwang-Hwan
authors: KH
authors: Jung
authors: Shigeyuki
authors: S
authors: Yokoyama
authors: Naoki
authors: N
authors: Kamo
mesh_terms: D000076:Acetabularia / Q000378:metabolism*; D000595:Amino Acid Sequence; D001190:Arylsulfonates / Q000737:chemistry; D002474:Cell-Free System; D018076:DNA, Complementary / Q000378:metabolism; D004566:Electrodes; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008027:Light; D008956:Models, Chemical; D008969:Molecular Sequence Data; D010777:Photochemistry / Q000379:methods*; D011522:Protons; D012243:Rhodopsin / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid; D017971:Tin Compounds / Q000737:chemistry
chemical_list: D001190:Arylsulfonates; D018076:DNA, Complementary; D011522:Protons; D017971:Tin Compounds; D012243:Rhodopsin; C005047:pyranine; C045358:stannic oxide