An anomalous distance dependence of intraprotein chlorophyll-carotenoid triplet energy transfer |
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| Authors: | Kim Hanyoup Dashdorj Naranbaatar Zhang Huamin Yan Jiusheng Cramer William A Savikhin Sergei |
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| Affiliation: | * Department of Physics, Purdue University, West Lafayette, IN 47907
† Department of Biological Sciences, Purdue University, West Lafayette, IN 47907 |
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| Abstract: | In the light-harvesting chlorophyll pigment-proteins of photosynthesis, a carotenoid is typically positioned within a distance of ~4 Å of individual chlorophylls or antenna arrays, allowing rapid triplet energy transfer from chlorophyll to the carotenoid. This triplet energy transfer prevents the formation of toxic singlet oxygen. In the cytochrome b6f complex of oxygenic photosynthesis that contains a single chlorophyll a molecule, this chlorophyll is distant (14 Å) from the single β-carotene, as defined by x-ray structures from both a cyanobacterium and a green alga. Despite this separation, rapid (<8 ns) long-range triplet energy transfer from the chlorophyll a to β-carotene is documented in this study, in seeming violation of the existing theory for the distance dependence of such transfer. We infer that a third molecule, possibly oxygen trapped in an intraprotein channel connecting the chlorophyll a and β-carotene, can serve as a mediator in chlorophyll-carotenoid triplet energy transfer in the b6f complex. |
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