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The photochemistry in photosystem II at 5 K is different in visible and far-red light
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
2014 (English)In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 53, no 26, 4228-4238 p.Article in journal (Refereed) Published
Abstract [en]

We have earlier shown that all electron transfer reactions in Photosystem II are operational up to 800 nm at room temperature [Thapper, A., et al. (2009) Plant Cell 21, 2391-2401]. This led us to suggest an alternative charge separation pathway for far-red excitation. Here we extend these studies to a very low temperature (5 K). Illumination of Photosystem II(PS II) with visible light at 5 K is known to result in oxidation of almost similar amounts of YZ and the Cyt b559/ChlZ/CarD2pathway. This is reproduced here using laser flashes at 532 nm, and we find the partition ratio between the two pathways to be 1:0.8 at 5 K [the partition ratio is here defined as (yield of YZ/CaMn4 oxidation):(yield of Cyt b559/ChlZ/CarD2 oxidation)]. The result using far-red laser flashes is very different. We find partition ratios of 1.8 at 730 nm, 2.7 at 740 nm, and >2.7 at 750 nm. No photochemistry involving these pathways is observed above 750 nm at this temperature. Thus, far-redillumination preferentially oxidizes YZ, while the Cyt b559/ChlZ/CarD2 pathway is hardly touched. We propose that the difference in the partition ratio between visible and far-red light at 5 K reflects the formation of a different first stable charge pair. In visible light, the first stable charge pair is considered to be PD1+QA-. In contrast, we propose that the electron hole is residing on the ChlD1 molecule after illumination by far-red light at 5 K, resulting in the first stable charge pair being ChlD1+QA-. ChlD1 is much closer to YZ (11.3 Å) than to any component in the Cyt b559/ChlZ/CarD2 pathway (shortest ChlD1-CarD2 distance of 28.8 Å). This would then explain that far-red illumination preferentially drives efficient electron transfer from YZ. We also discuss mechanisms for accounting for the absorption of the far-red light and the existence of hitherto unobserved charge transfer states. The involvement of two or more of the porphyrin molecules in the core of thePhotosystem II reaction center is proposed.

Place, publisher, year, edition, pages
2014. Vol. 53, no 26, 4228-4238 p.
National Category
Other Chemistry Topics
Research subject
Chemistry with specialization in Molecular Biomimetics
Identifiers
URN: urn:nbn:se:uu:diva-212116DOI: 10.1021/bi5006392ISI: 000338806100002PubMedID: 24918985OAI: oai:DiVA.org:uu-212116DiVA: diva2:676345
Available from: 2013-12-05 Created: 2013-12-05 Last updated: 2017-12-06Bibliographically approved
In thesis
1. The Far-Red Limit of Photosynthesis
Open this publication in new window or tab >>The Far-Red Limit of Photosynthesis
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The photosynthetic process has the unique ability to capture energy from sunlight and accumulate that energy in sugars and starch. This thesis deals with the light driven part of photosynthesis. The aim has been to investigate how the light-absorbing protein complexes Photosystem I (PS I) and Photosystem II (PS II), react upon illumination of light with lower energy (far-red light; 700-850 nm) than the absorption peak at respective primary donor, P700 and P680.  The results were unexpected. At 295 K, we showed that both PS I and PS II were able to perform photochemistry with light up to 130 nm above its respective primary donor absorption maxima. As such, it was found that the primary donors’ action spectra extended approximately 80 nm further out into the red-region of the spectrum than previously reported.  The ability to perform photochemistry with far-red light was conserved at cryogenic temperatures (< 77 K) in both photosystems. By performing EPR measurements on various photosystem preparations, under different illumination conditions the origin of the effect was localized to their respective reaction center. It is also likely that underlying mechanism is analogous for PS I and PS II, given the similarities in spatial coordination of the reaction center pigments. For PS II, the results obtained allowed us to suggest a model involving a previously unknown electron transfer pathway. This model is based upon the conclusion that the primary cation from primary charge separation induced by far-red light resides primarily on ChlD1 in P680. This is in contrast to the cation being located on PD1, as has been suggested as for visible light illumination.

The property to drive photochemistry with far-red wavelengths implies a hither to unknown absorption band, probably originating from the pigments that compose P700 and P680. The results presented here might clarify how the pigments inside P680 are coupled and also how the complex charge separation processes within the first picoseconds that initiate photosynthetic reactions occur.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 77 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1108
Keyword
Far-red light, Photosystem I, Photosystem II, P700, P680, EPR, Charge Separation
National Category
Natural Sciences Other Chemistry Topics
Research subject
Chemistry with specialization in Molecular Biomimetics
Identifiers
urn:nbn:se:uu:diva-213659 (URN)978-91-554-8835-2 (ISBN)
Public defence
2014-02-07, Siegbahnsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2014-01-16 Created: 2014-01-02 Last updated: 2014-01-24

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Mokvist, FredrikSjöholm, JohannesMamedov, FikretStyring, Stenbjörn

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