- Email: [email protected]
P-E1-13 Relaxation of the triplet state of P680 in photosystem II
El The photosynthetic reaction centre P-El-14 SPECTIWSCOPlC INYESTIGATIGNOF THE
P-El-13 RELAXATIQN OF THE TRIPLET STATE OF p6%0 INPEKMPOSW~ II VAN KAN, P.J.M., PETERSON. S. and STYRIN.G,S. . I$p;~nmchennstry. w .
REACTIUN B ACTERKA
PRBSE R N’,ALBOUY D2, ROBERT B2, VAN GRONDELLE R’ ‘Dept. of Physicsand Astronomy, Vrije Universiteit, Amsterdam (NL). 2Centre d’Etudes de Saclay (F)
Chemical Center, Lund University
Purpose: Characterisation of the spin-polarised triplet state 3P68O. which results from charge recombination in Photosystem II in plants. The main issues are the localisation of this state on one or more Chl a molecules and the orientation of these molecules in the photosynthetic membrane.
Purpose:To investigate the nature of the special pair and the intrinsic antenna pigments of different, low-BChla. preparations of the Reaction Center of photosynthetic green-sulphur bacteria. Methods: Ciiular Dichroism and Linear Dichroism measurements, Stark spectroscopy,Triplet minus Singlet delta absorption spectroscopyto probe the spatial organization and mutual interactions of the pigments.
Methods: Pulsed and cw EPR techniques are used in combination with flash excitation of Photosystem II. Experiments are performed in various preparations. Relaxation is studied by analysis of the kinetics of the EPR signals and the nuclear modulation on thesesignals.
Results: LD and Stark measurementsshow the heterogeneity of the P840 band: (at least) two diffemnt pigment pools. The red most absorbing pool is probably an excitation energy trap as revealed by T-S delta absorption measurements. CD and Stark measurementsindicate that the arrangement of the intrinsic anknna pigments is like PM0 The homodimeric nature of this Reaction Center is reflected in the difference dipole moment of the P840 band.
Results: Relaxation of this recombination triplet state is enhancedby interactions with the protein environment. EPR spectrum and kinetics can be explained by dimeric models.
Conclusions: All preparations are capable of primary charge transfer but show a different degree of association of antenna pigments. The P840 band is heterogeneous. There is a possible role of mixed in Charge Transfer states in electron transfer from P84O to Ch1670.There is a possible symmetry breaking by internal antenna pigments
Conclusions: The photochemically active Chl a molecules in PhotosystemII derive their special properties from the interaction with the protein rather than from an unusual molecular structure.
P-El-16 EFFECT OF BACKGRQW~ bd&UMJNAIN TION MEM ERS OF ~~~A~~~.~~~. VAN BREWRODE ME’, VAN STOKKUM IHM’, JONESMR2, VAN GRONDBLLE R’.
P-El-15
INFORMATIONINVOLVEB KUSUNOKI
M,t SRIQNO
Kv’ kLQBGAWA
&p. phys.,Wiji univ.. Kw&#@
Group, Inst. Phys.ckm. Res.,waki7h
CENTER OF THE GREEN-SULFUR CHLOR63BIUM LiMX0I.A
K?
%olar BtsargyRes.
‘Dcpr of Physicsand Astronomy Vrije Univetsiteit Amsterdam (I%). ‘Dept. of Molecular Biology and Biotechnology, University of ShefIield (UK).
Purpose: To investigateconformational changes associatedwith the fotmation of the chw separatedstateP+&- in photosynrhetic bae&rhd [email protected]). Mathods For RCs cooled down in the dark the P+QA-recombination rate Or,)is studied as a function of background illumination intensity between 77Kandroomtempecature.Thetruevaluekrin the presenceof background &mina$ion follows from the measurementof the fraction of open RCs and the observedrate of recombinoGon Results: At 77 K k, is constantas a function of background illumination intensity. At room ternperaturek, decreasesupon increasinglight intensity. ConeQ&ms: At room temperature the RCs perform a conformational change upon charge scpadon. w&h rtfploas ~WIa &IW soak slower thin the charg8 tkW&%i&ion.
148
P-El-13 RELAXATIQN OF THE TRIPLET STATE OF p6%0 INPEKMPOSW~ II VAN KAN, P.J.M., PETERSON. S. and STYRIN.G,S. . I$p;~nmchennstry. w .
REACTIUN B ACTERKA
PRBSE R N’,ALBOUY D2, ROBERT B2, VAN GRONDELLE R’ ‘Dept. of Physicsand Astronomy, Vrije Universiteit, Amsterdam (NL). 2Centre d’Etudes de Saclay (F)
Chemical Center, Lund University
Purpose: Characterisation of the spin-polarised triplet state 3P68O. which results from charge recombination in Photosystem II in plants. The main issues are the localisation of this state on one or more Chl a molecules and the orientation of these molecules in the photosynthetic membrane.
Purpose:To investigate the nature of the special pair and the intrinsic antenna pigments of different, low-BChla. preparations of the Reaction Center of photosynthetic green-sulphur bacteria. Methods: Ciiular Dichroism and Linear Dichroism measurements, Stark spectroscopy,Triplet minus Singlet delta absorption spectroscopyto probe the spatial organization and mutual interactions of the pigments.
Methods: Pulsed and cw EPR techniques are used in combination with flash excitation of Photosystem II. Experiments are performed in various preparations. Relaxation is studied by analysis of the kinetics of the EPR signals and the nuclear modulation on thesesignals.
Results: LD and Stark measurementsshow the heterogeneity of the P840 band: (at least) two diffemnt pigment pools. The red most absorbing pool is probably an excitation energy trap as revealed by T-S delta absorption measurements. CD and Stark measurementsindicate that the arrangement of the intrinsic anknna pigments is like PM0 The homodimeric nature of this Reaction Center is reflected in the difference dipole moment of the P840 band.
Results: Relaxation of this recombination triplet state is enhancedby interactions with the protein environment. EPR spectrum and kinetics can be explained by dimeric models.
Conclusions: All preparations are capable of primary charge transfer but show a different degree of association of antenna pigments. The P840 band is heterogeneous. There is a possible role of mixed in Charge Transfer states in electron transfer from P84O to Ch1670.There is a possible symmetry breaking by internal antenna pigments
Conclusions: The photochemically active Chl a molecules in PhotosystemII derive their special properties from the interaction with the protein rather than from an unusual molecular structure.
P-El-16 EFFECT OF BACKGRQW~ bd&UMJNAIN TION MEM ERS OF ~~~A~~~.~~~. VAN BREWRODE ME’, VAN STOKKUM IHM’, JONESMR2, VAN GRONDBLLE R’.
P-El-15
INFORMATIONINVOLVEB KUSUNOKI
M,t SRIQNO
Kv’ kLQBGAWA
&p. phys.,Wiji univ.. Kw&#@
Group, Inst. Phys.ckm. Res.,waki7h
CENTER OF THE GREEN-SULFUR CHLOR63BIUM LiMX0I.A
K?
%olar BtsargyRes.
‘Dcpr of Physicsand Astronomy Vrije Univetsiteit Amsterdam (I%). ‘Dept. of Molecular Biology and Biotechnology, University of ShefIield (UK).
Purpose: To investigateconformational changes associatedwith the fotmation of the chw separatedstateP+&- in photosynrhetic bae&rhd [email protected]). Mathods For RCs cooled down in the dark the P+QA-recombination rate Or,)is studied as a function of background illumination intensity between 77Kandroomtempecature.Thetruevaluekrin the presenceof background &mina$ion follows from the measurementof the fraction of open RCs and the observedrate of recombinoGon Results: At 77 K k, is constantas a function of background illumination intensity. At room ternperaturek, decreasesupon increasinglight intensity. ConeQ&ms: At room temperature the RCs perform a conformational change upon charge scpadon. w&h rtfploas ~WIa &IW soak slower thin the charg8 tkW&%i&ion.
148