Site-selective spectroscopy and level ordering in C-phycocyanine

Friedrich, J.; Fischer, Richard W.; Scheer, Hugo

doi:10.1016/0009-2614(88)87032-5

Cited by 18 publications

(4 citation statements)

References 19 publications

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“…This seems particularly important for EET involving C-706 and P700 since their SDF are close in energy (Table ). Our NPHB results (see also paper I) indicate that the Q y states of PSI, like those of other photosystems (see, for example, refs , , , −36) exhibit little, if any, such correlation. They show that burning a relatively sharp ZPH (selecting a narrow isochromat) into a higher energy absorption band results in broad low-energy satellite holes in the absorption bands of lower energy states.…”

Section: Resultsmentioning

confidence: 49%

Red Chlorophyll a Antenna States of Photosystem I of the Cyanobacterium Synechocystis sp. PCC 6803

et al. 2000

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The antenna chlorophyll a (Chl a) molecules of photosystem I of green plants and cyanobacteria that absorb further to the red than P700, the special pair of the reaction center, have long been of considerable interest. Recently, the results of nonphotochemical hole burning experiments at liquid helium temperatures, which included use of high pressure and external electric (Stark) fields, led to the conclusion that the cyanobacterium Synechocystis sp. PCC 6803 possesses two "red" antenna states whose S 0 (ground state) f Q y (S 1 ) origin absorption bands are at 714 and ≈708 nm (Ra ¨tsep et al. J. Phys. Chem B 2000, 104, 836). The results indicated that the 714 nm state is due to strongly coupled Chl a molecules (C-714), a dimer or, possibly, a trimer. It was concluded that the 714 nm state is responsible for the fluorescence origin band at 720 nm. Presented here are the results of theoretical simulations of the dependence of the hole spectra on burn wavelength and burn fluence that are consistent with the conclusions of Ra ¨tsep et al. They lead to a more detailed characterization of the two states, including determination of their site distribution functions (SDF) and the electron-phonon coupling parameters of the S 0 f Q y transitions. The higher energy state is found to lie closer to 706 nm than 708 nm. The electron-phonon coupling of the 714 nm transition is strong with a total Huang-Rhys factor (S t ) of 2.0 due to low-frequency modes at 18 and ≈70 cm -1 . The coupling of the 706 nm transition is weaker by a factor of 1.5. It is concluded that both C-714 and C-706 are, at a minimum, dimers that are not in close proximity to each other. The large widths, ≈300 cm -1 , of the SDF suggest that the structures of C-706 and C-714 are fragile. The spectroscopic properties of P700, C-706, and C-714 are compared and discussed in terms of excitation energy transfer at low temperatures. A new model that explains why only about half of the PS I complexes undergo irreversible charge separation in the low-temperature limit following excitation of the higher energy bulk antenna states is presented.

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Section: Resultsmentioning

confidence: 49%

Red Chlorophyll a Antenna States of Photosystem I of the Cyanobacterium Synechocystis sp. PCC 6803

et al. 2000

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“…In fact, in contrast to phytochromes, most phycobiliproteins [52], and all in this study, are not photoactive. The pigment binding sites in PBs are tightly packed, leaving no space for large configurational changes of pigments such as light-induced torsions of pyrrole rings involved in the photoconversion of phytochromes [53]. Thirdly, a reversible change in the protonation state of the PB pigments also fails to explain the far-red states in PBs.…”

Section: Discussionmentioning

confidence: 99%

Charge transfer states in phycobilisomes

Wahadoszamen¹,

Krüger²,

Ara³

et al. 2020

Biochimica et Biophysica Acta (BBA) - Bioenergetics

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“…The remaining fraction of ß' ** a sites have to relax from the |-> state to the ground state by emission or internal conversion. The results of several low-temperature hole-burning studies provide evidence for inhomogeneous broadening in phycobiliproteins;43"47 in Cphycocyanin hexamers, Kohler et al 46 observed sharp zero-phonon holes and interpreted them in terms of an inhomogeneous broadening mechanism due to microscopic disorder. One possible source for microscopic disorder in allophycocyanin ( ß)3 trimers would arise in the protein-protein packing between adjacent ß monomers.…”

Section: Discussionmentioning

confidence: 99%

Energy-transfer and exciton-state relaxation processes in allophycocyanin

Beck¹,

Sauer²

1992

J. Phys. Chem.

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4658region of the phase diagram, implying also an invariant total surfactant headgroup area in this region. These results were supported by QELS and SAXS measurements, which demonstrated that the micellar radius changes linearly with watersurfactant ratio, w,,. The measured total surfactant headgroup area agreed well with values estimated from phase boundary titration results. Conductivity measurements indicated no onset of percolation over the composition range studied. Above wo values J. Phys. Chem. 1992, 96, 4658-4666 of 5-7, the water in the reversed micellar cores had the properties of bulk water.Acknowledgment. This work was supported by the National Science ~oundation through a Presidential Young Investigator's Award to T.A.H., with matching funds from Dow Chemical Co.We have employed picosecond spectroscopic techniques to characterize the photophysics of the phycocyanobilin chromophores in linker-free allophycocyanin isolated from the cyanobacterium Synechococcus PCC 6301 (AN1 12 mutant). In analogy with the known structure of the related phycobiliprotein C-phycocyanin, allophycocyanin is probably organized as a ringlike homotrimer; the monomeric units are composed of an a and a ,9 subunit, each of which binds a phycocyanobilin chromophore via a thioether linkage to a cysteine residue at amino acid position 84. We observe bidirectional excitation transfer in the a,9 monomer between the a84 and ,984 chromophores with a 140-ps time constant. Absorption anisotropy measurements show that the transition dipole moments of the a84 and ,984 chromophores are tilted 13 * 9' apart in a@ monomers. In trimers, however, the a84 and 884 chromophores in adjacent a@ monomers are brought close together, forming strong chromophore-chromophore interactions across the intermonomer interface. We interpret the observed photophysics using a model consisting of exciton levels formed by mixing of the monomeric singlet-state levels of the a84 and ,984 chromophores in the trimers; a system of three symmetry-equivalent but well separated chromophore dimers is formed, which produces a pair of triply degenerate singlet exciton states. We assign an ultrafast ( q 2 -p~ time constant) anisotropy and photobleaching transient observed only in trimers to an interexciton level transition; the transient occurs with a polarization change that is consistent with a transition between the orthogonal upper and lower exciton states. The upper exciton state also relaxes directly to the ground state through a decay process with a 45-ps time constant. We attribute the heterogeneous relaxation of the upper exciton state through these two paths to an inhomogeneous broadening due to site heterogeneity, which was previously observed in C-phycocyanin in hole-burning experiments at low temperature (Kohler et al. Chem. Phys. Lett. 1988, 143, 169). Excited-state absorption, originating from the lower exciton state, is assigned to a transition yielding a doubly-excited exciton state (van Amerongen; Struve, J . Phys. Chem. 1991, 95, 9020). Excitation transfer a...

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Site-selective spectroscopy and level ordering in C-phycocyanine

Cited by 18 publications

References 19 publications

Red Chlorophyll a Antenna States of Photosystem I of the Cyanobacterium Synechocystis sp. PCC 6803

Red Chlorophyll a Antenna States of Photosystem I of the Cyanobacterium Synechocystis sp. PCC 6803

Charge transfer states in phycobilisomes

Energy-transfer and exciton-state relaxation processes in allophycocyanin

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