ИСТИНА

Time- and wavelength-correlated single photon counting and fs-absorption change measurements of the excitation dynamics were performed on phycobiliproteins (PBP) and whole cells of A.marina. The excited state population was simulated with a set of coupled linear differential equations. The overall energy transfer from PBP to the membrane intrinsic Chl d antenna was found to be limited by electronic excitation energy transfer (EET) along all coupled pigments in the PBP from the short wavelength phycocyanin (PC) molecules to the “terminal emitter” (TE) allophycocyanin (APC). Our results reveal that the EET step from TE in the PBP antenna to the first Chl d acceptor occurs with a time constant of 20 - 30 ps leading to a 70 - 80 ps time constant observed in the fluorescence decay which describes the overall (diffusive) EET from PBP to Chl d [1]. The overall EET is therefore limited by the diffusive EET along the PBP antenna. Based on a Förster type EET the distance between the TE in the PBP antenna and the first neighbour Chl d molecule is determined to be 2.7 nm for a 20 ps transfer step.