Chromophore Assignment in C-Phycocyanin from Mastigocladus laminosus

Siebzehnrübl, S.; Fischer, Richard W.; Scheer, Hugo

doi:10.1515/znc-1987-0315

Cited by 42 publications

(19 citation statements)

References 13 publications

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“…For the interpretation of our results, the information about the distance and mutual orientation between the chromophores can be taken into account [5], as well as the individual spectra of the a-84, /3-84 and /3-155 chromophores [20]. The spectrum of the a-84 chromophore has been determined by Siebzehnrfibl et al [21] on the isolated a-subunit and the spectra of the /3-chromophores were derived from a curve resolution of the absorption spectrum of the isolated /3-subunit [22]. From these data, F6rster energy-transfer rates for different pairs of chromophores in C-PC trimers including the nearest pairs of a-84 and /3-84 chromophores have been calculated [20,23].…”

Section: Discussionmentioning

confidence: 99%

“…where o.~, o-2 and o-3 are related to /3-155, a-84 and /3-84, respectively. Using y = 0.43 and the relative absorption cross-sections at 615 nm, as derived from the published absorption spectra of the individual chromophores [21,22], we obtain a value of 0.214 for r(~). This is in fair agreement with our experimental value of 0.23 + 0.02, although a 60 ° angle between dipoles is in better agreement with this value.…”

Section: Eiaai (T)mentioning

confidence: 99%

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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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Section: Discussionmentioning

confidence: 99%

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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“…Assuming that the three bilins of PC have the same absorbance, s at 295 ± 10 nm is 7450 M-1 cm-1 for the a subunit, 14,900 M-1 cm-1 for the 13 subunit, and 22,350 M-1lcm-1 for PC, as calculated from known £614 mm= 279,000 M-l cm-' for PC ac3 (8). The following 6295 (M-1lcm-1)values were used for other proteins: AP,19,500; PEC, 41,900; apomyoglobin,8,100; ribulosebisphosphate carboxylase,11,000; lysozyme,16,500. For tryptophan, 6295 .…”

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confidence: 99%

Ultraviolet-B photodestruction of a light-harvesting complex.

Lao

Glazer²

1996

Proc. Natl. Acad. Sci. U.S.A.

120

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Cyanobacteria are important contributors to global photosynthesis in both marine and terrestrial environments. Quantitative data are presented on UV-B-induced damage to the major cyanobacterial photosynthetic light harvesting complex, the phycobilisome, and to each of its constituent phycobiliproteins. The photodestruction quantum yield, 4¢295 nm. for the phycobiliproteins is high (_10-3, as compared with _10-7 for visible light). Energy transfer on a picosecond time scale does not compete with photodestruction. Photodamage to phycobilisomes in vitro and in living cells is amplified by causing dissociation and loss of function of the complex. In photosynthetic organisms, UV-B damage to lightharvesting complexes may significantly exceed that to DNA.In cells of nonphotosynthetic organisms, DNA absorbs '50% of the incident UV-B radiation and is the primary target of photodamage. However, in plants and photosynthetic organisms, chlorophyll and other pigments may contribute significantly to shielding of the DNA from ultraviolet radiation. For example, comparison of absolute action spectra for pyrimidine dimer formation in alfalfa seedlings versus T7 bacteriophage DNA show over a 100-fold decrease in the rate of UV-Binduced DNA damage (1). In cyanobacteria, the most widespread and abundant photosynthetic prokaryotes, we calculate that the light-harvesting proteins (phycobiliproteins and chlorophyll proteins) account for >99% of the UV-B absorption. There are voluminous data on the photochemistry of DNA and on quantum yields of its various photoreactions (e.g., ref. 2). Comparable data on the photodestruction quantum yields of proteins in general and light-harvesting proteins in particular are totally lacking.To address this deficiency, we present a quantitative study of the photodestruction of the cyanobacterial light-harvesting complex, the phycobilisome (3), by ultraviolet light of 285-305 nm at a photon flux for this 20-nm wavelength band about 50 times that reaching the Earth's surface at the normal stratospheric ozone level of about 300 Dobson units [matm-cm (1 atm = 101.33 kPa)] (4). Cyanobacteria make a dominant contribution to phytoplankton primary productivity. In the range from 285 to 700 nm, phycobilisomes account for over half of the absorption cross-section of cyanobacterial cells.Chlorophyll-protein complexes account for most of the remaining absorbance.As a test organism, we chose the extensively studied filamentous heterocystous cyanobacterium Anabaena strain PCC 7120. A schematic representation of the Anabaena phycobilisome is shown in Fig. 1. Allophycocyanin (AP) is the major component of the phycobilisome core (proximal to the reaction centers within the thylakoid membrane), and C-phycocyanin (PC), and phycoerythrocyanin (PEC) are the major and minor components of the rod substructures, respectively. We have studied the photochemistry of the individual phycobiliproteins, of the purified intact as well as dissociated phycobilisomes, and of phycobilisomes in living Anabaena cells. Spectroscop...

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“…Reaction with PCMS was performed by titration of heterohexameric PC (c& in a l.l-l.%-fold excess [26].…”

Section: Indirect Chromophore Modification With P-chloromerculy-bennementioning

confidence: 99%

“…The reaction of PC with mercurials selectively affects cysteine+lll (cys+lll) and also indirectly the neighbouring /3-84 chromophore [26]. While the (photo)chemical modifications mentioned above completely prevent heterohexamer formation, modification with PCMS, which binds to the single free cysteine cys-111 located at the p subunit near the &84 chromophore, causes only a moderately destabilizing effect on this aggregate.…”

Section: Indirect Chromophore Modification With Mercurialsmentioning

confidence: 99%

Dissociating effect of chromophore modifications on C-phycocyanin heterohexamers

Fischer

Scheer

1992

Journal of Photochemistry and Photobiology B: Biology

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The bilin chromophores of the a or /3 subunit of C-phycocyanin (PC) from Mastigocladus laminosus were modified, and subsequently recombined with the respective complementary unmodified chromophores. The modifications consisted of photobleaching (350 nm) or reversible reduction of the verdin-to rubin-type chromophore(s). Recombination led to heterodimers (a& but the heterohexameric aggregation state (a& could not be obtained with the modified chromophores. Autoxidation of the reduced a-84 chromophore in such a hybrid, which occurred on standing under aerobic conditions, induced reaggregation to heterohexamers. Chemical re-oxidation of the reduced chromophores did not produce reaggregation, and it was not promoted by a 22 kDa linker peptide fragment (Gottschalk et al., Photochem. Photobiol., 54 (1991) 283), which in unmodified samples stabilized heterohexameric aggregates. Binding of the mercurial p-chloromercury-benzenesulphonate to the single free cysteine of PC near (approximately 0.4 nm) the 884 chromophore had only a moderately destabilizing effect on the heterohexamer (a&. It was concluded that the intact chromophore structure is an important factor determining the quaternary structure of biliproteins. The tendency of heterohexamer destabilization is related to the situation in phycoerythrocyanin, where photoisomerization of the violobilin chromophore of the a subunit near the heterodimer-heterodimer contact region is also responsible for aggregate destabilization (Siebzehnriibl et al., Photochem. Photobiol., 46 (1989) 753).

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Chromophore Assignment in C-Phycocyanin from Mastigocladus laminosus

Cited by 42 publications

References 13 publications

Förster energy transfer between neighbouring chromophores in C-phycocyanin trimers

Förster energy transfer between neighbouring chromophores in C-phycocyanin trimers

Ultraviolet-B photodestruction of a light-harvesting complex.

Dissociating effect of chromophore modifications on C-phycocyanin heterohexamers

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