AutoriStefano Santabarbara, Alessandro Agostini, Anna Paola Casazza, Giuseppe Zucchelli, Donatella Carbonera
AbstractThe photo-excited triplet states of carotenoids, sensitised by triplet-triplet energy transfer from the chlorophyll
triplet states, have been investigated in the isolated Photosystem II (PSII) core complex and PSII-LHCII (Light
Harvesting Complex II) supercomplex by Optically Detected Magnetic Resonance techniques, using both
fluorescence (FDMR) and absorption (ADMR) detection. The absence of Photosystem I allows us to reach the
full assignment of the carotenoid triplet states populated in PSII under steady state illumination at low
temperature. Five carotenoid triplet (3Car) populations were identified in PSII-LHCII, and four in the PSII core
complex. Thus, four 3Car populations are attributed to ?-carotene molecules bound to the core complex. All of
them show associated fluorescence emission maxima which are relatively red-shifted with respect to the bulk
emission of both the PSII-LHCII and the isolated core complexes. In particular the two populations characterised
by Zero Field Splitting parameters |D| =0.0370-0.0373 cm-1/|E| = 0.00373-0.00375 cm-1 and |D|= 0.0381-
0.0385 cm-1/|E|=0.00393-0.00389 cm-1, are coupled by singlet energy transferwith chlorophyllswhich have
a red-shifted emission peaking at 705 nm. This observation supports previous suggestions that pointed towards
the presence of long-wavelength chlorophyll spectral forms in the PSII core complex. The fifth 3Car component is
observed only in the PSII-LHCII supercomplex and is then assigned to the peripheral light harvesting system.
RivistaBiochimica Et Biophysica Acta. Bioenergetics
Impact factor0
Pagina inizio262
Pagina fine275
Linee di Ricerca IBFMD.P01.005.001