Excited State Mixing Effects in Transient Absorption Spectra of the Photosynthetic Light-Harvesting Complex II

Valkūnas, Leonas; Cervinskas, V.; Trinkunas, Gediminas; Maller, M. G.; Holzwarth, Alfred R.

doi:10.1007/978-94-011-3953-3_65

Cited by 3 publications

(3 citation statements)

References 5 publications

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“…In view of our observation that the 683-nm band disappears in the HL(A730)/HL(B714) connecting Chls mutant, this interpretation seems to be not correct. Later, Melkozernov et al (2001) proposed that the 678-( 675) and 683-nm bands originate from borrowing of the oscillator strength from the excited state absorption of a Chl dimer to a nearby Chl monomer (Valkunas et al, 1999;van Amerongen et al, 2000). Our studies on the WT and the HL(A730)/HL(B714) mutant do not exclude this interpretation.…”

Section: Chlorophyll Dimers Neighboring the Etc Chlorophyllscontrasting

confidence: 65%

“…These two bands were originally assigned to the upper excitonic states of two Chl dimers located in the vicinity of the RC (Melkozernov et al, 2000b). Later, it was suggested that the two resonant bands originate from a borrowing of the oscillator strength from the excited-state absorption of Chl dimers to the ground-state absorption of nearby Chl monomers (Melkozernov et al, 2001; see also Valkunas et al (1999)). Similar transient DA bands were reported for PSI from C. reinhardtii strain CC2696 after excitation at 700 nm and 10 K. However, these two bands were accompanied by two other negative bands at 667 nm and 695 nm and four positive bands between 635 and 661 nm (Gibasiewicz et al, 2002).…”

Section: Introductionmentioning

confidence: 95%

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Excitonic Interactions in Wild-Type and Mutant PSI Reaction Centers

Gibasiewicz

Ramesh

Lin

et al. 2003

Biophysical Journal

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Femtosecond excitation of the red edge of the chlorophyll a Q(Y) transition band in photosystem I (PSI), with light of wavelength > or = 700 nm, leads to wide transient (subpicosecond) absorbance changes: positive DeltaA between 635 and 665 nm, and four negative DeltaA bands at 667, 675, 683, and 695 nm. Here we compare the transient absorbance changes after excitation at 700, 705, and 710 nm at 20 K in several PSI preparations of Chlamydomonas reinhardtii where amino acid ligands of the primary donor, primary acceptor, or connecting chlorophylls have been mutated. Most of these mutations influence the spectrum of the absorbance changes. This supports the view that the chlorophylls of the electron transfer chain as well as the connecting chlorophylls are engaged in the observed absorbance changes. The wide absorption spectrum of the electron transfer chain revealed by the transient measurements may contribute to the high efficiency of energy trapping in photosystem 1. Exciton calculations, based on the recent PSI structure, allow an assignment of the DeltaA bands to particular chlorophylls: the bands at 675 and 695 nm to the dimers of primary acceptor and accessory chlorophyll and the band at 683 nm to the connecting chlorophylls. The subpicosecond transient absorption bands decay may reflect rapid charge separation in the PSI reaction center.

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Section: Chlorophyll Dimers Neighboring the Etc Chlorophyllscontrasting

confidence: 65%

Section: Introductionmentioning

confidence: 95%

Excitonic Interactions in Wild-Type and Mutant PSI Reaction Centers

Gibasiewicz

Ramesh

Lin

et al. 2003

Biophysical Journal

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“…Also, a great deal of steady-state and triplet spectroscopy has been performed (Barzda et al, 1998;Gülen et al, 1997;Peterman et al, 1995Peterman et al, , 1996Peterman et al, , 1997aNussberger et al, 1994). Several papers have been devoted primarily to elaborate modeling of the spectroscopic kinetic data on the basis of the known structure details (Gradinaru et al, 1998;Gülen et al, 1997;Visser et al, 1996;Trinkunas et al, 1997Trinkunas et al, -1999Valkunas et al, 1998Valkunas et al, , 1999. However, despite that substantial amount of work, no complete picture about the Chl organization, the pigment-pigment coupling, and the functional role of the carotenoids has been obtained.…”

Section: Introductionmentioning

confidence: 99%

Carotenoid-to-Chlorophyll Energy Transfer in Recombinant Major Light-Harvesting Complex (LHCII) of Higher Plants. I. Femtosecond Transient Absorption Measurements

Croce

Müller

Bassi

et al. 2001

Biophysical Journal

210

215

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The energy transfer kinetics from carotenoids to chlorophylls and among chlorophylls has been measured by femtosecond transient absorption kinetics in a monomeric unit of the major light-harvesting complex (LHCII) from higher plants. The samples were reconstituted complexes with different carotenoid contents. The kinetics was measured both in the carotenoid absorption region and in the chlorophyll Q(y) region using two different excitation wavelengths suitable for selective excitation of the carotenoids. Analysis of the data shows that the overwhelming part of the energy transfer from the carotenoids occurs directly from the initially excited S(2) state of the carotenoids. Only a small part (<20%) may possibly take an S(1) pathway. All the S(2) energy transfer from carotenoids to chlorophylls occurs with time constants <100 fs. We have been able to differentiate among the three carotenoids, two luteins and neoxanthin, which have transfer times of approximately 50 and 75 fs for the two luteins, and approximately 90 fs for neoxanthin. About 50% of the energy absorbed by carotenoids is initially transferred directly to chlorophyll b (Chl b), while the rest is transferred to Chl a. Neoxanthin almost exclusively transfers to Chl b. Due to various complex effects discussed in the paper, such as a specific coupling of Chl b and Chl a excited states, the percentage of direct Chl b transfer thus is somewhat lower than estimated by us previously for LHCII from Arabidopsis thaliana. (Connelly, J. P., M. G. Müller, R. Bassi, R. Croce, and A. R. Holzwarth. 1997. Biochemistry. 36:281). We can distinguish three different Chls b receiving energy directly from carotenoids. We propose as a new mechanism that the carotenoid-to-Chl b transfer occurs to a large part via the B(x) state of Chl b and to the Q(x) state, while the transfer to Chl a occurs only via the Q(x) state. We find no compelling evidence in favor of a substantial S(1) transfer path of the carotenoids, although some transfer via the S(1) state of neoxanthin can not be entirely excluded. The S(1) lifetimes of the two luteins were determined to be 15 ps and 3.9 ps. A detailed quantitative analysis and kinetic model of the processes described here will be presented in a separate paper.

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