title: Triplet state dynamics in peridinin-chlorophyll-a-protein: a new pathway of photoprotection in LHCs?
abstract: This work investigates the interaction of carotenoid and chlorophyll triplet states in the peridinin-chlorophyll-a-protein (PCP) of Amphidinium carterae using step-scan Fourier transform infrared spectroscopy. We identify two carotenoid triplet state lifetimes of approximately 13 and approximately 42 mus in the spectral region between 1800 and 1100 cm(-1) after excitation of the 'blue' and 'red' peridinin (Per) conformers and the Q(y) of chlorophyll-a (Chl-a). 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 1745 cm(-1). One (1720 cm(-1)) and two (1720 cm(-1) and 1741 cm(-1)) different Per conformers are observed for the slow component upon 670- and 530-480-nm excitation, respectively. The above result implies that (3)Per triplets are formed via two different pathways, corroborating and complementing visible triplet-singlet (T-S) spectra (Kleima et al., Biochemistry (2000), 39, 5184). Surprisingly, all difference spectra show that Per and Chl-a modes are simultaneously present during the (3)Per decay, implying significant involvement of (3)Chl-a in the (3)Per state. We suggest that this Per-Chl-a interaction via a delocalized triplet state lowers the (3)Per energy and thus provides a general, photoprotection mechanism for light-harvesting antenna complexes.
authors.affiliation: Department of Biophysics and Physics of Complex Systems, Division of Physics and Astronomy, Faculty of Sciences, Vrije Universiteit, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
authors.forename: Maxime T A
authors.initials: MT
authors.lastname: Alexandre
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Lührs
authors.forename: Ivo H M
authors.initials: IH
authors.lastname: van Stokkum
authors.forename: Roger
authors.initials: R
authors.lastname: Hiller
authors.forename: Marie-Louise
authors.initials: ML
authors.lastname: Groot
authors.forename: John T M
authors.initials: JT
authors.lastname: Kennis
authors.forename: Rienk
authors.initials: R
authors.lastname: van Grondelle
mesh_terms: D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D002338:Carotenoids / Q000737:chemistry*; D004141:Dinoflagellida / Q000737:chemistry; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D008956:Models, Chemical; D015394:Molecular Structure; D010777:Photochemistry; D015800:Protozoan Proteins / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013816:Thermodynamics
chemical_list: D045342:Light-Harvesting Protein Complexes; D015800:Protozoan Proteins; C073227:peridinin chlorophyll-a protein, Dinophyceae; D002338:Carotenoids