Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
1942129 | Biochimica et Biophysica Acta (BBA) - Bioenergetics | 2015 | 12 Pages |
Abstract
Room (298 K) and low (77 K) 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 (~ 5Ã) samples at both 298 and 77 K. No concentration induced alterations in the flash-induced absorption changes were observed. Concentrated samples in short path-length cells form a transparent film at 77 K, and could therefore be studied spectroscopically at 77 K without addition of a cryoprotectant. At 298 K, for photosystem I with plastoquinone 9/menadione/phylloquinone incorporated, P700+FA/Bâ radical pair recombination is characterized by a time constant of 3/14/80 ms, and forward electron transfer from A1Aâ to Fx by a time constant of 211/3.1/0.309 μs, respectively. At 77 K, for concentrated photosystem I with menadione/phylloquinone incorporated, P700+A1â 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.
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Authors
Hiroki Makita, Nan Zhao, Gary Hastings,