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- Rate of Carotenoid Triplet Formation in Solubilized Light-Ha...Rate of Carotenoid Triplet Formation in Solubilized Light-Harvesting Complex II (LHCII) from Spinach
Biophysical Journal, Volume 75, Issue 6, 1 December 1998, Pages 3143-3153
René Schödel, Klaus-D. Irrgang, Joachim Voigt and Gernot Renger
AbstractIn the present study the rate of triplet transfer from chlorophyll to carotenoids in solubilized LHCII was investigated by flash spectroscopy using laser pulses of ∼2ns for both pump and probe. Special attention has been paid to calibration of the experimental setup and to avoid saturation effects. Carotenoid triplets were identified by the pronounced positive peak at ∼507nm in the triplet-singlet difference spectra. Δ (507nm) exhibits a monoexponential relaxation kinetics with characteristic lifetimes of 2–9s (depending on the oxygen content) that was found to be independent of the pump pulse intensity. The rise of Δ (507nm) was resolved via a pump probe technique where an optical delay of up to 20ns was used. A thorough analysis of these experimental data leads to the conclusion that the kinetics of carotenoid triplet formation in solubilized LHCII is almost entirely limited by the lifetime of the excited singlet state of chlorophyll but neither by the pulse width nor by the rate constant of triplet-triplet transfer. Within the experimental error the rate constant of triplet-triplet transfer from chlorophyll to carotenoids was estimated to be >(0.5ns). This value exceeds all data reported so far by at least one order of magnitude. The implications of this finding are briefly discussed.
Abstract | Full Text | PDF (193 kb) - Quenching of Chlorophyll Fluorescence by Triplets in Solubil...Quenching of Chlorophyll Fluorescence by Triplets in Solubilized Light-Harvesting Complex II (LHCII)
Biophysical Journal, Volume 76, Issue 4, 1 April 1999, Pages 2238-2248
René Schödel, Klaus-D. Irrgang, Joachim Voigt and Gernot Renger
AbstractThe quenching of chlorophyll fluorescence by triplets in solubilized trimeric light harvesting complexes was analyzed by comparative pump-probe experiments that monitor with weak 2-ns probe pulses the fluorescence yield and changes of optical density, Δ induced by 2-ns pump pulses. By using a special array for the measurement of the probe fluorescence (Schödel R., F. Hillman, T. Schrötter, K.-D. Irrgang, J. Voight, and G. Renger, 1996. 71:3370–3380) the emission caused by the pump pulses could be drastically reduced so that even at highest pump pulse intensities, , no significant interference with the signal due to the probe pulse was observed. The data obtained reveal: a) at a fixed time delay of 50ns between pump and probe pulse the fluorescence yield of the latter drastically decreased with increasing , b) the recovery of the fluorescence yield in the s time domain exhibits kinetics which are dependent on , c) Δ at 507nm induced by the pump pulse and monitored by the probe pulse with a delay of 50ns (reflecting carotenoid triplets) increases with without reaching a saturation level at highest values, d) an analogous feature is observed for the bleaching at 675nm but it becomes significant only at very high values, e) the relaxation of Δ at 507nm occurs via a monophasic kinetics at all values whereas Δ at 675nm measured under the same conditions is characterized by a biphasic kinetics with values of about 1s and 7–9s. The latter corresponds with the monoexponential decay kinetics of Δ at 507nm. Based on a Stern-Volmer plot, the time-dependent fluorescence quenching is compared with the relaxation kinetics of triplets. It is shown that the fluorescence data can be consistently described by a quenching due to triplets.
Abstract | Full Text | PDF (187 kb) - Triplet State Dynamics in Peridinin-Chlorophyll-a-Protein: A...Triplet State Dynamics in Peridinin-Chlorophyll-a-Protein: A New Pathway of Photoprotection in LHCs?
Biophysical Journal, Volume 93, Issue 6, 15 September 2007, Pages 2118-2128
Maxime T.A. Alexandre, Daniel C. Lührs, Ivo H.M. van Stokkum, Roger Hiller, Marie-Louise Groot, John T.M. Kennis and Rienk van Grondelle
AbstractThis work investigates the interaction of carotenoid and chlorophyll triplet states in the peridinin-chlorophyll--protein (PCP) of using step-scan Fourier transform infrared spectroscopy. We identify two carotenoid triplet state lifetimes of ∼13 and ∼42s in the spectral region between 1800 and 1100cm after excitation of the ‘blue’ and ‘red’ peridinin (Per) conformers and the Q of chlorophyll- (Chl-). The fast and slow decaying triplets exhibit different spectral signatures in the carbonyl region. The fast component generated at all excitation wavelengths is from a major conformer with a lactone stretching mode bleach at 1745cm. One (1720cm) and two (1720cm and 1741cm) different Per conformers are observed for the slow component upon 670- and 530–480-nm excitation, respectively. The above result implies that Per triplets are formed via two different pathways, corroborating and complementing visible triplet-singlet (T-S) spectra (Kleima et al., Biochemistry (2000), , 5184). Surprisingly, all difference spectra show that Per and Chl- modes are simultaneously present during the Per decay, implying significant involvement of Chl- in the Per state. We suggest that this Per-Chl- interaction via a delocalized triplet state lowers the Per energy and thus provides a general, photoprotection mechanism for light-harvesting antenna complexes.
Abstract | Full Text | PDF (168 kb) - …more
Copyright © 1995 The Biophysical Society. All rights reserved.
Biophysical Journal, Volume 69, Issue 6, 2670-2678, 1 December 1995
doi:10.1016/S0006-3495(95)80138-4
Research Article
Chlorophyll a and carotenoid triplet states in light-harvesting complex II of higher plants
E.J. Peterman, F.M. Dukker, R. van Grondelle and H. van Amerongen
Abstract
Laser-flash-induced transient absorption measurements were performed on trimeric light-harvesting complex II to study carotenoid (Car) and chlorophyll (Chl) triplet states as a function of temperature. In these complexes efficient transfer of triplets from Chl to Car occurs as a protection mechanism against singlet oxygen formation. It appears that at room temperature all triplets are being transferred from Chl to Car; at lower temperatures (77 K and below) the transfer is less efficient and chlorophyll triplets can be observed. In the presence of oxygen at room temperature the Car triplets are partly quenched by oxygen and two different Car triplet spectral species can be distinguished because of a difference in quenching rate. One of these spectral species is replaced by another one upon cooling to 4 Ki demonstrating that at least three carotenoids are in close contact with chlorophylls. The triplet minus singlet absorption (T-S) spectra show maxima at 504–506 nm and 517–523 nm, respectively. In the Chl Qy region absorption changes can be observed that are caused by Car triplets. The T-S spectra in the Chl region show an interesting temperature dependence which indicates that various Car's are in contact with different Chl a molecules. The results are discussed in terms of the crystal structure of light-harvesting complex II.
