Quenching of chlorophyll a singlets and triplets by carotenoids in light-harvesting complex of photosystem II

Comparison of aggregates with trimers

K. Razi Naqvi, T. B. Melø, B. Bangar Raju, Tamás Jávorfi, Ilian Simidjiev, G. Garab

Research output: Contribution to journalArticle

42 Citations (Scopus)

Abstract

Laser-induced changes in the absorption spectra of isolated light-harvesting chlorophyll a/b complex (LHC II) associated with photosystem II of higher plants have been recorded under anaerobic conditions and at ambient temperature by using multichannel detection with sub-microsecond time resolution. Difference spectra (AA) of LHC II aggregates have been found to differ from the corresponding spectra of trimers on two counts: (i) in the aggregates, the carotenoid (Car) triplet-triplet absorption band (ΔA > 0) is red-shifted and broader; and (ii) the features attributable to the perturbation of the Qy band of a chlorophyll a (Chla) by a nearby Car triplet are more pronounced, than in trimers. Aggregation, which is known to be accompanied by a reduction in the fluorescence yield of Chla, is shown to cause a parallel decline in the triplet formation yield of Chla; on the other hand, the efficiency (100%) of Chla-to-Car transfer of triplet energy and the lifetime (9.3 μs) of Car triplets are not affected by aggregation. These findings are rationalized by postulating that the antenna Cars transact, besides light-harvesting and photoprotection, a third process: energy dissipation within the antenna. The suggestion is advanced that luteins, which are buried inside the LHC II monomers, as well as the other, peripheral, xanthophylls (neoxanthin and violaxanthin) quench the excited singlet state of Chla by catalyzing internal conversion, a decay channel that competes with fluorescence and intersystem crossing; support for this explanation is presented by recalling reports of similar behaviour in bichromophoric model compounds in which one moiety is a Car and the other a porphyrin or a pyropheophorbide.

Original languageEnglish
Pages (from-to)2659-2667
Number of pages9
JournalSpectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy
Volume53
Issue number14
Publication statusPublished - Dec 1997

Fingerprint

carotenoids
Photosystem II Protein Complex
chlorophylls
Chlorophyll
Carotenoids
trimers
Quenching
quenching
Absorption spectra
Agglomeration
antennas
Fluorescence
Xanthophylls
Antennas
absorption spectra
fluorescence
Porphyrins
internal conversion
Excited states
porphyrins

Keywords

  • Chlorophyll-carotenoid interaction
  • Light-harvesting complex
  • Photosynthesis

ASJC Scopus subject areas

  • Spectroscopy

Cite this

Quenching of chlorophyll a singlets and triplets by carotenoids in light-harvesting complex of photosystem II : Comparison of aggregates with trimers. / Razi Naqvi, K.; Melø, T. B.; Bangar Raju, B.; Jávorfi, Tamás; Simidjiev, Ilian; Garab, G.

In: Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy, Vol. 53, No. 14, 12.1997, p. 2659-2667.

Research output: Contribution to journalArticle

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title = "Quenching of chlorophyll a singlets and triplets by carotenoids in light-harvesting complex of photosystem II: Comparison of aggregates with trimers",
abstract = "Laser-induced changes in the absorption spectra of isolated light-harvesting chlorophyll a/b complex (LHC II) associated with photosystem II of higher plants have been recorded under anaerobic conditions and at ambient temperature by using multichannel detection with sub-microsecond time resolution. Difference spectra (AA) of LHC II aggregates have been found to differ from the corresponding spectra of trimers on two counts: (i) in the aggregates, the carotenoid (Car) triplet-triplet absorption band (ΔA > 0) is red-shifted and broader; and (ii) the features attributable to the perturbation of the Qy band of a chlorophyll a (Chla) by a nearby Car triplet are more pronounced, than in trimers. Aggregation, which is known to be accompanied by a reduction in the fluorescence yield of Chla, is shown to cause a parallel decline in the triplet formation yield of Chla; on the other hand, the efficiency (100{\%}) of Chla-to-Car transfer of triplet energy and the lifetime (9.3 μs) of Car triplets are not affected by aggregation. These findings are rationalized by postulating that the antenna Cars transact, besides light-harvesting and photoprotection, a third process: energy dissipation within the antenna. The suggestion is advanced that luteins, which are buried inside the LHC II monomers, as well as the other, peripheral, xanthophylls (neoxanthin and violaxanthin) quench the excited singlet state of Chla by catalyzing internal conversion, a decay channel that competes with fluorescence and intersystem crossing; support for this explanation is presented by recalling reports of similar behaviour in bichromophoric model compounds in which one moiety is a Car and the other a porphyrin or a pyropheophorbide.",
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AU - Melø, T. B.

AU - Bangar Raju, B.

AU - Jávorfi, Tamás

AU - Simidjiev, Ilian

AU - Garab, G.

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AB - Laser-induced changes in the absorption spectra of isolated light-harvesting chlorophyll a/b complex (LHC II) associated with photosystem II of higher plants have been recorded under anaerobic conditions and at ambient temperature by using multichannel detection with sub-microsecond time resolution. Difference spectra (AA) of LHC II aggregates have been found to differ from the corresponding spectra of trimers on two counts: (i) in the aggregates, the carotenoid (Car) triplet-triplet absorption band (ΔA > 0) is red-shifted and broader; and (ii) the features attributable to the perturbation of the Qy band of a chlorophyll a (Chla) by a nearby Car triplet are more pronounced, than in trimers. Aggregation, which is known to be accompanied by a reduction in the fluorescence yield of Chla, is shown to cause a parallel decline in the triplet formation yield of Chla; on the other hand, the efficiency (100%) of Chla-to-Car transfer of triplet energy and the lifetime (9.3 μs) of Car triplets are not affected by aggregation. These findings are rationalized by postulating that the antenna Cars transact, besides light-harvesting and photoprotection, a third process: energy dissipation within the antenna. The suggestion is advanced that luteins, which are buried inside the LHC II monomers, as well as the other, peripheral, xanthophylls (neoxanthin and violaxanthin) quench the excited singlet state of Chla by catalyzing internal conversion, a decay channel that competes with fluorescence and intersystem crossing; support for this explanation is presented by recalling reports of similar behaviour in bichromophoric model compounds in which one moiety is a Car and the other a porphyrin or a pyropheophorbide.

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