Identification of the Sites of Chlorophyll Triplet Quenching in Relation to the Structure of LHC-II from Higher Plants. Evidence from EPR Spectroscopy

The Chlorophyll a (Chl a) molecules involved in the triplet-triplet energy transfer to the central luteins in trimeric LHC-II are identified by time-resolved and pulse EPR techniques. The concept of, spin angular momentum conservation during triplet-triplet energy transfer is exploited for the calculation of the spin polarization of the carotenoid triplet states. The sites with the highest probability of forming triplet states, which are quenched by the central luteins, result to be Chl603 and Chl612. Unquenched Chl triplet states are produced by photoexcitation in the LHC-II complex. Putative sites of these triplet states are Chl614, Chl611, Chl604, and Chl613 since they do not contribute to the formation of the observed carotenoid triplet states.