TY - JOUR
T1 - Observation of the Reduction and Reoxidation of the Primary Electron Acceptor in Photosystem I
AU - Hastings, Gary
AU - Kleinherenbrink, Frank A M
AU - Lin, Su
AU - McHugh, Thomas J.
AU - Blankenship, Robert E.
PY - 1994/3/1
Y1 - 1994/3/1
N2 - Femtosecond transient absorption spectroscopy has been used to investigate the primary charge separation in a photosystem II deletion mutant from the cyanobacterium Synechocystis sp. PCC 6803. These cells contain only the photosystem I reaction center and have a pigment content of ∼ 100 chlorophylls per P700. Utilizing relatively high excitation intensities, the difference spectrum for the reduction of primary electron acceptor [(A0− – A0) difference spectrum] was obtained from experiments performed under both reducing and oxidizing conditions. Both approaches yield very similar results with the (A0− – A0) difference spectrum displaying a maximum bleaching at 687 nm. The shape of the difference spectrum suggests that the primary electron acceptor in photosystem I may be a chlorophyll a molecule. The observed rate of primary radical pair formation depends on the overall rate of decay of excitations in the antenna; the radical pair state forms as the antenna decays. The decay of the primary radical pair state is characterized by a 21 -ps time constant. Under conditions that avoid annihilation effects, the mean lifetime for excitations in the antenna is 28 ps [Hastings, G., Kleinherenbrink, F. A. M., Lin, S., & Blankenship, R. E. (1994) Biochemistry (preceding paper in this issue)]. This indicates that the reduced acceptor decays faster than it forms. Therefore, only a low concentration of the reduced acceptor will accumulate under most conditions.
AB - Femtosecond transient absorption spectroscopy has been used to investigate the primary charge separation in a photosystem II deletion mutant from the cyanobacterium Synechocystis sp. PCC 6803. These cells contain only the photosystem I reaction center and have a pigment content of ∼ 100 chlorophylls per P700. Utilizing relatively high excitation intensities, the difference spectrum for the reduction of primary electron acceptor [(A0− – A0) difference spectrum] was obtained from experiments performed under both reducing and oxidizing conditions. Both approaches yield very similar results with the (A0− – A0) difference spectrum displaying a maximum bleaching at 687 nm. The shape of the difference spectrum suggests that the primary electron acceptor in photosystem I may be a chlorophyll a molecule. The observed rate of primary radical pair formation depends on the overall rate of decay of excitations in the antenna; the radical pair state forms as the antenna decays. The decay of the primary radical pair state is characterized by a 21 -ps time constant. Under conditions that avoid annihilation effects, the mean lifetime for excitations in the antenna is 28 ps [Hastings, G., Kleinherenbrink, F. A. M., Lin, S., & Blankenship, R. E. (1994) Biochemistry (preceding paper in this issue)]. This indicates that the reduced acceptor decays faster than it forms. Therefore, only a low concentration of the reduced acceptor will accumulate under most conditions.
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U2 - 10.1021/bi00177a008
DO - 10.1021/bi00177a008
M3 - Article
C2 - 8136354
AN - SCOPUS:0028273452
SN - 0006-2960
VL - 33
SP - 3193
EP - 3200
JO - Biochemistry
JF - Biochemistry
IS - 11
ER -