MPS seminar Joseph Huges

Chasing Tails and the Primary Donor: Linking low temperature optical spectroscopy to physiological phenomena in Photosystem II.

Fri, 2009-05-08, 13.15, Lecture Hall B, KC.

Abstract:
   Results are presented outlining the discovery (1) of a low energy (700-730 nm), weak absorption band in higher plant PSII that was attributed to an optically accessible charge transfer transition of the reaction center.  Such an absorption band was subsequently a critical feature of a model (2) for the electronic structure of the Photosystem II reaction center and the pathway of primary charge separation.
   Unlike plants and algae, cyanobacteria exhibit small genes families (psbA1-5) that code for multiple copies of the D1 protein.  In Thermosynechococcus elongatus, high light conditions induce photoprotective acclimation by the preferential expression of psbA3 over psbA1, resulting in the replacement of the ‘normal growth’ D1:1 variant with D1:3.  A recent investigation of the optically accessible charge transfer transition and yield of the photoprotective side-pathway in T. elongatus D1: and D1:3 variants is presented.  The results indicate a correlation of the D1 variant with the energy of the charge transfer transition, and can be associated with amino acid changes between the D1:1 and D1:3 variants.  The quantum efficiency of the side-pathway is reduced in the low light variant, and could be explained by a variation in the location and/or redox potential of the long-lived P+ cation.

 (1) Hughes, J. L., Smith, P., Pace, R., and Krausz, E. (2006) Charge Separation in Photosystem II Core Complexes Induced by 690-730 nm Excitation at 1.7 K. Biochimica et Biophysica Acta 1757, 841-851.

 (2) Novoderezhkin, V. I., Dekker, J. P., and van Grondelle, R. (2007) Mixing of exciton and charge-transfer states in Photosystem II reaction centers: Modeling of stark spectra with modified redfield theory. Biophysical Journal 93, 1293-1311.

 

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