Exciton interaction in allophycocyanin

Csatorday, K.; MacColl, Robert; Csizmadia, Vilmos; Grabowski, J.; Bagyinka, Csaba

doi:10.1021/bi00321a029

Cited by 58 publications

(61 citation statements)

References 16 publications

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“…According to the first one (excitonic model), two excitonic states arise as a result of the splitting of the doubly degenerate S 1 electronic state of spectrally very similar a-80 and /3-81 chromophores. This idea was first proposed by MacColl and coworkers [17] and later further elaborated in fluorescence [18] and absorption [16] ultrafast measurements. In this model the trimer absorption spectrum as a whole belongs to both (a-80 and /3-81) spectrally nearly identical chromophores or, more correctly, to the excitonically coupled dimer formed upon aggregation.…”

Section: Discussionmentioning

confidence: 96%

Femtosecond spectral and anisotropy study of excitation energy transfer between neighbouring α-80 and β-81 chromophores of allophycocyanin trimers

Sharkov

Kryukov

Khoroshilov

et al. 1994

Biochimica et Biophysica Acta (BBA) - Bioenergetics

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Polarization pump-probe femtosecond spectroscopy was used to investigate photoinduced optical density changes in allophycocyanin (APC) trimers at 635-690 nm after excitation with 230-fs pulses at 618 nm. The initial bleaching observed at h < 645 nm is followed by subpicosecond absorption recovery corresponding to 430 + 40 fs recovery kinetics measured at 615 nm with 70-fs pulses. Only the red part of the APC absorption band remains strongly bleached at 3 ps after excitation. The spectral and kinetic results can be described in terms of two different models of interaction between neighbouring a-80 and /3-81 chromophores of APC trimers. According to the first one, the observed subpicosecond kinetics corresponds to relaxation between the levels of excitonically coupled, spectrally identical a-80 and/3-81 chromophores. Excited state absorption to doubly excited excitonic state should in this case contribute to the measured difference spectra. According to the second one, the femtosecond excitation energy transfer in APC trimers takes place between a donor chromophore absorbing predominantly at 620 nm and an acceptor chromophore absorbing at 650 nm. The high anisotropy value observed at 615 nm during the first 1.2 ps is in good agreement with the donor-acceptor model. Anisotropy values calculated in the 635-675 nm spectral region at 3 ps after excitation are in the 0.1-0.25 range corresponding to an angle of 30°-45 ° between donor and acceptor transition dipole orientations. The high anisotropy obtained at 658 nm during the excitation is probably due to stimulated emission of the donor chromophore.

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Section: Discussionmentioning

confidence: 96%

Femtosecond spectral and anisotropy study of excitation energy transfer between neighbouring α-80 and β-81 chromophores of allophycocyanin trimers

Sharkov

Kryukov

Khoroshilov

et al. 1994

Biochimica et Biophysica Acta (BBA) - Bioenergetics

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“…The 620 nm absorption band of the intact protein ( Fig. 1) has been assigned to the chromophores present in the ␣␤ dimers, whereas the 653 nm peak that appears when hexamer is formed has been attributed to exciton coupling between chromophores in adjacent ␣␤ dimers within the hexamer (MacColl et al, 1981;Csatorday et al 1984;Beck and Sauer, 1992). From the absorption at wavelengths longer than 620 nm, it follows that the integrated dimer absorbance is expected to be 0.27 of that of the hexamer while dissociation into denatured monomers would lower it further to less than 0.06 of the intact aggregate.…”

Section: Spectralmentioning

confidence: 99%

Pressure-induced Dissociation and Denaturation of Allophycocyanin at Subzero Temperatures

Foguel¹,

Weber²

1995

Journal of Biological Chemistry

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The thermodynamics of assembly of the allophycocyanin hexamer was examined employing hydrostatic pressures in the range of 1 bar to 2.4 kbar and temperatures of 20 to ؊12°C, the latter made possible by the decrease of the freezing point of water under pressure. The existence of two processes, dissociation of the hexamer into dimers, (␣␤) 3 3 3 (␣␤), and dissociation of the ␣␤ dimers into monomers, (␣␤) 3 ␣ ؉ ␤ have been recognized previously by changes in the absorbance and fluorescence of the tetrapyrrolic chromophores owing to added ligands. The same changes are observed in the absence of ligands at pressures of under 2.4 kbar and temperatures down to ؊12°C. On decompression from 2.4 kbar at 0°C, appreciable hysteresis and a persistent loss of 50% in the absorbance at 653 nm is observed. It results from the conformational drift of the isolated subunits and is reduced to 10% when the highest pressure is limited to 1.6 kbar. The thermodynamic parameters of the reaction ␣ ؉ ␤ 3 ␣␤ can be determined from pressure effects on perchlorate solutions of allophycocyanin, which consist of dimers alone. Their previous knowledge permits estimation, under suitable hypotheses, of the thermodynamic parameters of the reaction 3(␣␤) 3 (␣␤) 3 from the overall pressure effects on the hexamers. Both association reactions have positive enthalpy changes, and the whole hexamer assembly is made possible by the excess entropy.Allophycocyanin is one of the phycobiliproteins of phycobilisomes, the accessory light-harvesting complexes in cyanobacteria and red algae. Allophycocyanin has been isolated as a trimeric species (␣␤) 3 (Zilinskas et al., 1978;MacColl et al., 1981) of 110 kDa to which we shall refer here as a hexamer. Conversion of (␣␤) 3 into ␣␤ dimers is obtained by the addition of 1 M perchlorate (MacColl et al., 1971;MacColl et al., 1981;Huang et al., 1987) or by lowering the pH (MacColl et al., 1980). Dissociation of ␣␤ dimers into ␣ ϩ ␤ monomers has been achieved only in the presence of urea at 8 M concentration (Erokhima and Krasnoviskii, 1974).Hydrostatic pressure has been used successfully to explore the thermodynamics and mechanism of assembly of oligomeric proteins. (Silva and Weber, 1993). In this report, we describe how the dissociation of (␣␤) 3 into ␣␤ dimers and then into ␣ ϩ ␤ monomers occurs when the solutions of the protein are subjected to hydrostatic pressures in the range of atmospheric to 3 kbar and temperatures in the range of 10 to Ϫ11°C. The decrease in the freezing point of water under pressure makes it possible to reach a temperature of Ϫ20°C at 2.4 kbar while maintaining the liquid state. In the absence of perchlorate or urea, complete dissociation of allophycocyanin takes place only at these low temperatures, and this has enabled us to show that the process of dimer dissociation by the cold results in a state very similar to that obtained by addition of a classical chemical denaturant, urea, but as a freely displaceable equilibrium. Separation of the two sequential processes of hexamer and dimer disso...

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“…In APC trimers an excitonic coupling between the a-and fl-chromophores has been suggested as an explanation for the shape of the CD-spectrum around 650 nm [26][27][28][29]. An alternative explanation would be that the circular dichroism is due to a specific conformation of one of the chromophores [27].…”

Section: Eiaai (T)mentioning

confidence: 99%

Förster energy transfer between neighbouring chromophores in C-phycocyanin trimers

Gillbro

Sharkov

Kryukov

et al. 1993

Biochimica et Biophysica Acta (BBA) - Bioenergetics

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The excitation-energy transfer in C-phycocyanin (C-PC) trimers and monomers isolated from phycobilisomes of Mastigocladus laminosus has been studied by polarization femtosecond laser spectroscopy. Excitation with 70-fs pulses at 615 nm gave rise to a 500-fs energy-transfer process that was observed only in trimeric preparations. The rate of the process is in agreement with earlier calculated F6rster energy transfer rates between neighbouring a-84 and /3-84 chromophores of different monomeric subunits. This process is most clearly seen in the anisotropy decay kinetics. As a result of femtosecond excitation-energy transfer, the anisotropy relaxes from 0.4 to 0.23. The final anisotropy value is in fair agreement with the results of calculations based on the crystal structure and spectroscopic data of C-PC trimers. Our results support the conclusion that F6rster energy transfer can occur between excitonically coupled chromophores.

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Exciton interaction in allophycocyanin

Cited by 58 publications

References 16 publications

Femtosecond spectral and anisotropy study of excitation energy transfer between neighbouring α-80 and β-81 chromophores of allophycocyanin trimers

Femtosecond spectral and anisotropy study of excitation energy transfer between neighbouring α-80 and β-81 chromophores of allophycocyanin trimers

Pressure-induced Dissociation and Denaturation of Allophycocyanin at Subzero Temperatures

Förster energy transfer between neighbouring chromophores in C-phycocyanin trimers

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