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Issue 25, 2009
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Electron transfer from A 0 to A1 in Photosystem I from Chlamydomonas reinhardtii occurs in both the A and B branch with 25–30-ps lifetime

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Abstract

We have recorded transient absorption kinetics at 390 nm with picosecond resolution in order to observe electron transfer from the reduced primary acceptor, A0, to the secondary acceptor, A1, in wild type and mutated Photosystem I from Chlamydomonas reinhardtii. In the mutants, the methionine axial ligand to the primary electron acceptor in either the A- or B-branch of electron transfer cofactors, was replaced with histidine. Both of the mutations reduced the formation of a positive signal at 390 nm, characteristic of A1 to a level approximately half of that observed in wild type Photosystem I. It is concluded that in the mutated branch of Photosystem I, electron transfer from A0 to A1 does not occur. The absorption kinetics resulting from subtraction of either of the mutants’ traces from that of wild type is interpreted to reflect the kinetics of A- or B-side electron transfer from A0 to A1 in the the wild type Photosystem I. Each of these traces could be fitted with a monoexpoenential decay characterized by the same amplitude and 25–30-ps lifetime. The almost identical effect of both mutations on A1 formation confirm a similar engagement of both the A- ad B-branches in electron transfer to A1 in Photosystem I from C. reinhardtii. This observation is in contrast to the unidirectional electron transfer concluded from the studies on similar mutants of cyanobacterial Photosystem I.1 Thus, this contribution provides further evidence for functional differences between these two model Photosystems.

Graphical abstract: Electron transfer from A−0 to A1 in Photosystem I from Chlamydomonas reinhardtii occurs in both the A and B branch with 25–30-ps lifetime

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Article information


Submitted
19 Dec 2008
Accepted
16 Mar 2009
First published
09 Apr 2009

Phys. Chem. Chem. Phys., 2009,11, 5186-5191
Article type
Paper

Electron transfer from A0 to A1 in Photosystem I from Chlamydomonas reinhardtii occurs in both the A and B branch with 25–30-ps lifetime

W. Giera, K. Gibasiewicz, V. M. Ramesh, S. Lin and A. Webber, Phys. Chem. Chem. Phys., 2009, 11, 5186
DOI: 10.1039/B822938D

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