Excitation Energy Transfer in the Phycobiliprotein Antenna of Acaryochloris marina Studied by Transient fs Absorption and Fluorescence Spectroscopy

Abstract

We investigated the excitation energy transfer (EET) in the phycobiliprotein (PBP) antenna of the Chl d-containing cyanobacterium Acaryochloris marina. The equilibration of the excitation energy over all phycocyanin (PC) and allophycocyanin (APC) molecules of the PBPantenna in A. marina was found to occur with time constants of < 400 fs, 3 ps and 14 ps. This is more than ten times faster than the EET from the PC rod-antenna to the APC core in typical cyanobacteria with phycobilisomes as Synechococcus 6301 (Holzwarth 1991). These results are in agreement with the unique structure of the PBP-antenna of A. marina which consists of three PC-homohexamers and one hetero-hexamer containing PC and APC (Marquardt et al. 1997). The results suggest that the presence of APC and PC within one hexamer, which has so far been observed only in A. marina, enables a very fast 3 ps EET from PC to APC, thereby facilitating a fast energy transfer from phycobiliproteins to PS II with a time constant of 70 ps (Petrasek et al. 2005).