TY - JOUR
T1 - Redox study of electron donation to P-680 in Photosystem II
AU - Golbeck, John H.
AU - Warden, Joseph T.
N1 - Funding Information:
The experimental work was supported, in part, by a grant (to J.T.W.) from the National Institute of Health (2R01 GM26133-04). Funding for the interpretation of the data and writing of the manuscript was provided (to J.H.G.) from the National Science Foundation (PCM-8304610). The technical assistance of Mrs. Sundararaman is gratefully appreciated. Acknowledgment is also made to Dr. Paul Mathis for helpful discussions.
PY - 1985/1/23
Y1 - 1985/1/23
N2 - Flash-induced absorption changes at 820 nm were studied as a function of redox potential in Tris-extracted Photosystem II oxygen-evolving particles and Triton subchloroplast fraction II particles. The rereduction kinetics of P-680+ in both preparations showed biphasic recovery phases with half-times of 42 and 625 μs at pH 4.5. The magnitude of the 42 μs phase of P-680+ rereduction was strongly dependent on the redox potential of the medium. This absorption transient, attributed to electron donation from D1 (the secondary electron donor in oxygen-inhibited chloroplasts), titrated as a single redox component with a midpoint potential of +240 ± 35 mV. The experimentally determined midpoint potential was found to be independent of pH over the tested range 4.5-6.0. In contrast, the magnitude of the 625 μs phase of P-680+ rereduction was independent of redox potential between +350 and +100 mV. These results are interpreted in terms of a model in which an alternate electron donor with Em ≈ 240 mV, termed D0, serves as a rapid donor (t 1 2 ≤ 2 μs) to P-680+ in Tris-extracted and Triton-treated Photosystem-II preparations. According to this model, the slower electron donor, D1, is functional only when D0 becomes oxidized.
AB - Flash-induced absorption changes at 820 nm were studied as a function of redox potential in Tris-extracted Photosystem II oxygen-evolving particles and Triton subchloroplast fraction II particles. The rereduction kinetics of P-680+ in both preparations showed biphasic recovery phases with half-times of 42 and 625 μs at pH 4.5. The magnitude of the 42 μs phase of P-680+ rereduction was strongly dependent on the redox potential of the medium. This absorption transient, attributed to electron donation from D1 (the secondary electron donor in oxygen-inhibited chloroplasts), titrated as a single redox component with a midpoint potential of +240 ± 35 mV. The experimentally determined midpoint potential was found to be independent of pH over the tested range 4.5-6.0. In contrast, the magnitude of the 625 μs phase of P-680+ rereduction was independent of redox potential between +350 and +100 mV. These results are interpreted in terms of a model in which an alternate electron donor with Em ≈ 240 mV, termed D0, serves as a rapid donor (t 1 2 ≤ 2 μs) to P-680+ in Tris-extracted and Triton-treated Photosystem-II preparations. According to this model, the slower electron donor, D1, is functional only when D0 becomes oxidized.
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U2 - 10.1016/0005-2728(85)90087-8
DO - 10.1016/0005-2728(85)90087-8
M3 - Article
C2 - 3967006
AN - SCOPUS:0022430816
VL - 806
SP - 116
EP - 123
JO - Biochimica et Biophysica Acta - Bioenergetics
JF - Biochimica et Biophysica Acta - Bioenergetics
SN - 0005-2728
IS - 1
ER -