Model for fluorescence quenching in light harvesting complex II in different aggregation states |
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Authors: | Atanaska Andreeva Silvia Abarova Katerina Stoitchkova Mira Busheva |
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Institution: | (1) Department of Condensed Matter Physics, Faculty of Physics, Sofia University, 5, J. Bourchier blvd., 1164 Sofia, Bulgaria;(2) Institute of Biophysics, Bulgarian Academy of Sciences, Acad. G. Bonchev str. bl.21, 1113 Sofia, Bulgaria |
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Abstract: | Low-temperature (77 K) steady-state fluorescence emission spectroscopy and dynamic light scattering were applied to the main
chlorophyll a/b protein light harvesting complex of photosystem II (LHC II) in different aggregation states to elucidate the mechanism of
fluorescence quenching within LHC II oligomers. Evidences presented that LHC II oligomers are heterogeneous and consist of
large and small particles with different fluorescence yield. At intermediate detergent concentrations the mean size of the
small particles is similar to that of trimers, while the size of large particles is comparable to that of aggregated trimers
without added detergent. It is suggested that in small particles and trimers the emitter is monomeric chlorophyll, whereas
in large aggregates there is also another emitter, which is a poorly fluorescing chlorophyll associate. A model, describing
populations of antenna chlorophyll molecules in small and large aggregates in their ground and first singlet excited states,
is considered. The model enables us to obtain the ratio of the singlet excited-state lifetimes in small and large particles,
the relative amount of chlorophyll molecules in large particles, and the amount of quenchers as a function of the degree of
aggregation. These dependencies reveal that the quenching of the chl a fluorescence upon aggregation is due to the formation of large aggregates and the increasing of the amount of chlorophyll
molecules forming these aggregates. As a consequence, the amount of quenchers, located in large aggregates, is increased,
and their singlet excited-state lifetimes steeply decrease. |
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Keywords: | Light harvesting complex II 77 K chlorophyll fluorescence Aggregation Fluorescence quenching |
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