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Oxygen-evolving Photosystem II core complexes: a new paradigm based on the spectral identification of the charge-separating state, the primary acceptor and assignment of low-temperature fluorescence

Krausz, E; Hughes, JL; Smith, P; Pace, R and Peterson Årsköld, Sindra LU (2005) In Photochemical and Photobiological Sciences 4(9). p.744-753
Abstract
We review our recent low-temperature absorption, circular dichroism ( CD), magnetic CD (MCD), fluorescence and laser-selective measurements of oxygen-evolving Photosystem II ( PSII) core complexes and their constituent CP43, CP47 and D1/D2/cytb(559) sub-assemblies. Quantitative comparisons reveal that neither absorption nor fluorescence spectra of core complexes are simple additive combinations of the spectra of the sub-assemblies. The absorption spectrum of the D1/D2/cytb(559) component embedded within the core complex appears significantly better structured and red-shifted compared to that of the isolated sub-assembly. A characteristic MCD reduction or 'deficit' is a useful signature for the central chlorins in the reaction centre. We... (More)
We review our recent low-temperature absorption, circular dichroism ( CD), magnetic CD (MCD), fluorescence and laser-selective measurements of oxygen-evolving Photosystem II ( PSII) core complexes and their constituent CP43, CP47 and D1/D2/cytb(559) sub-assemblies. Quantitative comparisons reveal that neither absorption nor fluorescence spectra of core complexes are simple additive combinations of the spectra of the sub-assemblies. The absorption spectrum of the D1/D2/cytb(559) component embedded within the core complex appears significantly better structured and red-shifted compared to that of the isolated sub-assembly. A characteristic MCD reduction or 'deficit' is a useful signature for the central chlorins in the reaction centre. We note a congruence of the MCD deficit spectra of the isolated D1/D2/cytb(559) sub-assemblies to their laser-induced transient bleaches associated with P680. A comparison of spectra of core complexes prepared from different organisms helps distinguish features due to inner light-harvesting assemblies and the central reaction-centre chlorins. Electrochromic spectral shifts in core complexes that occur following low-temperature illumination of active core complexes arise from efficient charge separation and subsequent plastoquinone anion (Q(A)(-)) formation. Such measurements allow determinations of both charge-separation efficiencies and spectral characteristics of the primary acceptor, Pheo(D1). Efficient charge separation occurs with excitation wavelengths as long as 700 nm despite the illuminations being performed at 1.7 K and with an extremely low level of incident power density. A weak, homogeneously broadened, charge-separating state of PSII lies obscured beneath the CP47 state centered at 690 nm. We present new data in the 690 - 760 nm region, clearly identifying a band extending to 730 nm. Active core complexes show remarkably strong persistent spectral hole-burning activity in spectral regions attributable to CP43 and CP47. Measurements of homogeneous hole-widths have established that, at low temperatures, excitation transfer from these inner light-harvesting assemblies to the reaction centre occurs with similar to 70 - 270 ps(-1) rates, when the quinone acceptor is reduced. The rate is slower for lower-energy sub-populations of an inhomogeneously broadened antenna ( trap) pigment. The complex low-temperature fluorescence behaviour seen in PSII is explicable in terms of slow excitation transfer from traps to the weak low-energy charge-separating state and transfer to the more intense reaction-centre excitations near 685 nm. The nature and origin of the charge-separating state in oxygen-evolving PSII preparations is briefly discussed. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Photochemical and Photobiological Sciences
volume
4
issue
9
pages
744 - 753
publisher
Royal Society of Chemistry
external identifiers
  • wos:000231449900015
  • scopus:25444508945
ISSN
1474-9092
DOI
10.1039/b417905f
language
English
LU publication?
yes
id
ea6fd86f-d88b-429f-bb26-95da3ffa311f (old id 226556)
date added to LUP
2007-08-21 08:16:58
date last changed
2017-09-17 05:21:32
@article{ea6fd86f-d88b-429f-bb26-95da3ffa311f,
  abstract     = {We review our recent low-temperature absorption, circular dichroism ( CD), magnetic CD (MCD), fluorescence and laser-selective measurements of oxygen-evolving Photosystem II ( PSII) core complexes and their constituent CP43, CP47 and D1/D2/cytb(559) sub-assemblies. Quantitative comparisons reveal that neither absorption nor fluorescence spectra of core complexes are simple additive combinations of the spectra of the sub-assemblies. The absorption spectrum of the D1/D2/cytb(559) component embedded within the core complex appears significantly better structured and red-shifted compared to that of the isolated sub-assembly. A characteristic MCD reduction or 'deficit' is a useful signature for the central chlorins in the reaction centre. We note a congruence of the MCD deficit spectra of the isolated D1/D2/cytb(559) sub-assemblies to their laser-induced transient bleaches associated with P680. A comparison of spectra of core complexes prepared from different organisms helps distinguish features due to inner light-harvesting assemblies and the central reaction-centre chlorins. Electrochromic spectral shifts in core complexes that occur following low-temperature illumination of active core complexes arise from efficient charge separation and subsequent plastoquinone anion (Q(A)(-)) formation. Such measurements allow determinations of both charge-separation efficiencies and spectral characteristics of the primary acceptor, Pheo(D1). Efficient charge separation occurs with excitation wavelengths as long as 700 nm despite the illuminations being performed at 1.7 K and with an extremely low level of incident power density. A weak, homogeneously broadened, charge-separating state of PSII lies obscured beneath the CP47 state centered at 690 nm. We present new data in the 690 - 760 nm region, clearly identifying a band extending to 730 nm. Active core complexes show remarkably strong persistent spectral hole-burning activity in spectral regions attributable to CP43 and CP47. Measurements of homogeneous hole-widths have established that, at low temperatures, excitation transfer from these inner light-harvesting assemblies to the reaction centre occurs with similar to 70 - 270 ps(-1) rates, when the quinone acceptor is reduced. The rate is slower for lower-energy sub-populations of an inhomogeneously broadened antenna ( trap) pigment. The complex low-temperature fluorescence behaviour seen in PSII is explicable in terms of slow excitation transfer from traps to the weak low-energy charge-separating state and transfer to the more intense reaction-centre excitations near 685 nm. The nature and origin of the charge-separating state in oxygen-evolving PSII preparations is briefly discussed.},
  author       = {Krausz, E and Hughes, JL and Smith, P and Pace, R and Peterson Årsköld, Sindra},
  issn         = {1474-9092},
  language     = {eng},
  number       = {9},
  pages        = {744--753},
  publisher    = {Royal Society of Chemistry},
  series       = {Photochemical and Photobiological Sciences},
  title        = {Oxygen-evolving Photosystem II core complexes: a new paradigm based on the spectral identification of the charge-separating state, the primary acceptor and assignment of low-temperature fluorescence},
  url          = {http://dx.doi.org/10.1039/b417905f},
  volume       = {4},
  year         = {2005},
}