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
(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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https://lup.lub.lu.se/record/226556
- author
- Krausz, E ; Hughes, JL ; Smith, P ; Pace, R and Peterson Årsköld, Sindra LU
- organization
- publishing date
- 2005
- 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
- 2016-04-01 12:26:45
- date last changed
- 2022-01-27 03:49:39
@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}},
doi = {{10.1039/b417905f}},
volume = {{4}},
year = {{2005}},
}