title: Time-resolved visible and infrared difference spectroscopy for the study of photosystem I with different quinones incorporated into the A1 binding site.
abstract: Room (298 K) and low (77K) temperature time-resolved visible and infrared difference spectroscopy has been used to study photosystem I particles with phylloquinone (2-methyl-3-phytyl-1,4-naphthoquinone), menadione (2-methyl-1,4-naphthoquinone) and plastoquinone 9 (2,3-dimethyl-5-prenyl-l,4-benzoquinone), incorporated into the A1 binding site. Concentrated samples in short path-length (~5 μm) sample cells are typically used in FTIR experiments. Measurements were undertaken using standard "dilute" samples at 298 K, and concentrated (~5×) samples at both 298 and 77K. No concentration induced alterations in the flash-induced absorption changes were observed. Concentrated samples in short path-length cells form a transparent film at 77K, and could therefore be studied spectroscopically at 77K without addition of a cryoprotectant. At 298 K, for photosystem I with plastoquinone 9/menadione/phylloquinone incorporated, P700+FA/B- radical pair recombination is characterized by a time constant of 3/14/80 ms, and forward electron transfer from A1A- to Fx by a time constant of 211/3.1/0.309 μs, respectively. At 77K, for concentrated photosystem I with menadione/phylloquinone incorporated, P700+A1- radical pair recombination is characterized by a time constant of 240/340 μs, with this process occurring in 58/39% of the PSI particles, respectively. The origin of these differences is discussed. Marcus electron transfer theory in combination with kinetic modeling is used to simulate the observed electron transfer time constants at 298 K. This simulation allows an estimate of the redox potential for the different quinones in the A1 binding site.
authors.affiliation: Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303, USA.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Makita
authors.affiliation: Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303, USA.
authors.forename: Nan
authors.initials: N
authors.lastname: Zhao
authors.affiliation: Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303, USA. Electronic address: ghastings@gsu.edu.
authors.forename: Gary
authors.initials: G
authors.lastname: Hastings
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D003198:Computer Simulation; D004579:Electron Transport; D007700:Kinetics; D008954:Models, Biological; D015394:Molecular Structure; D010084:Oxidation-Reduction; D045331:Photosystem I Protein Complex / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D011809:Quinones / Q000737:chemistry / Q000378:metabolism*; D013055:Spectrophotometry, Infrared; D046939:Synechocystis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D045331:Photosystem I Protein Complex; D011809:Quinones
keywords: A1; Electron transfer; FTIR; Photosystem I; Phylloquinone; Time resolved