Time-resolved visible and infrared difference spectroscopy for the study of photosystem I with different quinones incorporated into the A1 binding site

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-1,4-benzoquinone), incorporated into the A(1) binding site. Concentrated samples in short path-length (similar to 5 mu m) sample cells are typically used in FITR experiments. Measurements were undertaken using standard "dilute" samples at 298 K, and concentrated (similar to 5x) 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(+)F(A/B)(-) radical pair recombination is characterized by a time constant of 3/14/80 ms, and forward electron transfer from A(1A)(-) to F-x by a time constant of 211/3.1/0.309 mu s, respectively. At 77 K, for concentrated photosystem I with menadione/phylloquinone incorporated, P700(+)A(1)(-) radical pair recombination is characterized by a time constant of 240/340 mu s, 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 A(1) binding site. (C) 2014 Elsevier B.V. All rights reserved.