title: Triplet-triplet energy transfer in Peridinin-Chlorophyll a-protein reconstituted with Chl a and Chl d as revealed by optically detected magnetic resonance and pulse EPR: comparison with the native PCP complex from Amphidinium carterae.
abstract: The triplet state of the carotenoid peridinin, populated by triplet-triplet energy transfer from photoexcited chlorophyll triplet state, in the reconstituted Peridinin-Chlorophyll a-protein, has been investigated by ODMR (Optically detected magnetic resonance), and pulse EPR spectroscopies. The properties of peridinins associated with the triplet state formation in complexes reconstituted with Chl a and Chl d have been compared to those of the main-form peridinin-chlorophyll protein (MFPCP) isolated from Amphidinium carterae. In the reconstituted samples no signals due to the presence of chlorophyll triplet states have been detected, during either steady state illumination or laser-pulse excitation. This demonstrates that reconstituted complexes conserve total quenching of chlorophyll triplet states, despite the biochemical treatment and reconstitution with the non-native Chl d pigment. Zero field splitting parameters of the peridinin triplet states are the same in the two reconstituted samples and slightly smaller than in native MFPCP. Analysis of the initial polarization of the photoinduced Electron-Spin-Echo detected spectra and their time evolution, shows that, in the reconstituted complexes, the triplet state is probably localized on the same peridinin as in native MFPCP although, when Chl d replaces Chl a, a local rearrangement of the pigments is likely to occur. Substitution of Chl d for Chl a identifies previously unassigned bands at approximately 620 and approximately 640 nm in the Triplet-minus-Singlet (T-S) spectrum of PCP detected at cryogenic temperature, as belonging to peridinin.
authors.affiliation: Dipartimento di Scienze Chimiche, Università di Padova, via Marzolo 1, 35131 Padova, Italy.
authors.forename: Marilena
authors.initials: M
authors.lastname: Di Valentin
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Agostini
authors.forename: Enrico
authors.initials: E
authors.lastname: Salvadori
authors.forename: Stefano
authors.initials: S
authors.lastname: Ceola
authors.forename: Giorgio Mario
authors.initials: GM
authors.lastname: Giacometti
authors.forename: Roger G
authors.initials: RG
authors.lastname: Hiller
authors.forename: Donatella
authors.initials: D
authors.lastname: Carbonera
mesh_terms: D000818:Animals; D002338:Carotenoids / Q000737:chemistry*; D002734:Chlorophyll / Q000737:chemistry*; D000077194:Chlorophyll A; D004141:Dinoflagellida / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D004735:Energy Transfer; D015800:Protozoan Proteins / Q000737:chemistry*
chemical_list: D015800:Protozoan Proteins; C073227:peridinin chlorophyll-a protein, Dinophyceae; D002734:Chlorophyll; C016040:peridinin; D002338:Carotenoids; C107509:chlorophyll d; D000077194:Chlorophyll A