Singlet and Triplet State Transitions of Carotenoids in the Antenna Complexes of Higher-Plant Photosystem I
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- 作者：Roberta Croce ; Milena Mozzo ; Tomas Morosinotto ; Alessandro Romeo ; Rainer Hienerwadel ; Roberto Bassi
- 刊名：Biochemistry
- 出版年：2007
- 出版时间：March 27, 2007
- 年：2007
- 卷：46
- 期：12
- 页码：3846 - 3855
- 全文大小：160K
- 年卷期：v.46,no.12(March 27, 2007)
- ISSN：1520-4995
文摘
In this work, the spectroscopic characteristics of carotenoids associated with the antennacomplexes of Photosystem I have been studied. Pigment composition, absorption spectra, and laser-inducedtriplet-minus-singlet (T-S) spectra were determined for native LHCI from the wild type (WT) and lut2mutant from Arabidopsis thaliana as well as for reconstituted individual Lhca WT and mutated complexes.All WT complexes bind lutein and violaxanthin, while 
-carotene was found to be associated only withthe native LHCI preparation and recombinant Lhca3. In the native complexes, the main lutein absorptionbands are located at 492 and 510 nm. It is shown that violaxanthin is able to occupy all lutein bindingsites, but its absorption is blue-shifted to 487 and 501 nm. The "red" lutein absorbing at 510 nm wasfound to be associated with Lhca3 and Lhca4 which also show a second carotenoid, peaking around 490nm. Both these xanthophylls are involved in triplet quenching and show two T-S maxima: one at 507nm (corresponding to the 490 nm singlet absorption) and the second at 525 nm (with absorption at 510nm). The "blue"-absorbing xanthophyll is located in site L1 and can receive triplets from chlorophylls(Chl) 1012, 1011, and possibly 1013. The red-shifted spectral component is assigned to a lutein moleculelocated in the L2 site. A 510 nm lutein was also observed in the trimers of LHCII but was absent in themonomers. In the case of Lhca, the 510 nm band is present in both the monomeric and dimeric complexes.We suggest that the large red shift observed for this xanthophyll is due to interaction with the neighborChl 1015. In the native T-S spectrum, the contribution of carotenoids associated with Lhca2 is visiblewhile the one of Lhca1 is not. This suggests that in the Lhca2-Lhca3 heterodimeric complex energyequilibration is not complete at least on a fast time scale.
-carotene was found to be associated only withthe native LHCI preparation and recombinant Lhca3. In the native complexes, the main lutein absorptionbands are located at 492 and 510 nm. It is shown that violaxanthin is able to occupy all lutein bindingsites, but its absorption is blue-shifted to 487 and 501 nm. The "red" lutein absorbing at 510 nm wasfound to be associated with Lhca3 and Lhca4 which also show a second carotenoid, peaking around 490nm. Both these xanthophylls are involved in triplet quenching and show two T-S maxima: one at 507nm (corresponding to the 490 nm singlet absorption) and the second at 525 nm (with absorption at 510nm). The "blue"-absorbing xanthophyll is located in site L1 and can receive triplets from chlorophylls(Chl) 1012, 1011, and possibly 1013. The red-shifted spectral component is assigned to a lutein moleculelocated in the L2 site. A 510 nm lutein was also observed in the trimers of LHCII but was absent in themonomers. In the case of Lhca, the 510 nm band is present in both the monomeric and dimeric complexes.We suggest that the large red shift observed for this xanthophyll is due to interaction with the neighborChl 1015. In the native T-S spectrum, the contribution of carotenoids associated with Lhca2 is visiblewhile the one of Lhca1 is not. This suggests that in the Lhca2-Lhca3 heterodimeric complex energyequilibration is not complete at least on a fast time scale.