These authors contributed equally to this work.
Additive Effect of Mutations Affecting the Rate of Phylloquinone Reoxidation and Directionality of Electron Transfer within Photosystem I†
Article first published online: 3 NOV 2008
© 2008 The Authors. Journal Compilation. The American Society of Photobiology
Photochemistry and Photobiology
Volume 84, Issue 6, pages 1381–1387, November/December 2008
How to Cite
Santabarbara, S., Jasaitis, A., Byrdin, M., Gu, F., Rappaport, F. and Redding, K. (2008), Additive Effect of Mutations Affecting the Rate of Phylloquinone Reoxidation and Directionality of Electron Transfer within Photosystem I. Photochemistry and Photobiology, 84: 1381–1387. doi: 10.1111/j.1751-1097.2008.00458.x
This invited paper is part of the Symposium-in-Print: Photosynthesis.
- Issue published online: 3 NOV 2008
- Article first published online: 3 NOV 2008
- Received 9 May 2008, accepted 25 August 2008
Optical pump-probe spectroscopy in the nanosecond–microsecond timescale has been used to study the electron transfer reactions taking place within the Photosystem I reaction center of intact Chlamydomonas reinhardtii cells. The biphasic kinetics of phylloquinone (PhQ) reoxidation were investigated in double mutants that combine a mutation (PsaA-Y696F) near the primary acceptor chlorophyll, ec3A, with those near PhQA (PsaA-S692A, PsaA-W697F). The PsaA-S692A and PsaA-W697F mutations selectively lengthened the 200 ns lifetime component observed in the wild-type (WT). The ?20 ns component was unaltered in the single mutant, both in terms of lifetime and relative amplitude. However, both double mutants possessed a ?20 ns component (PhQB− reoxidation) with increased amplitude compared with the WT and the individual PhQA mutants. The component assigned to PhQA− reoxidation was slowed, like the individual PhQA mutants, and of lower amplitude, as observed in the single ec3A mutant. Hence, the effects of these mutations are almost entirely additive, providing strong support for the previously proposed bidirectional electron transfer model, which attributes the ?20 and ?200 ns phases to reoxidation of PhQB or PhQA, respectively. Moreover, in all the mutants investigated, it was also possible to observe an intermediate (∼180 ns) component, as previously reported for mutants of the PhQA binding pocket (Biochim. Biophys. Acta  1757, 1529–1538), which we have tentatively attributed to forward electron transfer between the iron–sulfur clusters FX and FA/B.