Rates and pathways of energy migration from the phycobilisome to the photosystem II and to the orange carotenoid protein in cyanobacteria.

The phycobilisome (PBS) is the cyanobacterial antenna complex which transfers absorbed light energy to the photosystem II (PSII), while the excess energy is nonphotochemically quenched by interaction of the PBS with the orange carotenoid protein (OCP). Here, the molecular model of the PBS-PSII-OCP supercomplex was utilized to assess the resonance energy transfer from PBS to PSII and, using the excitonic theory, the transfer from PBS to OCP. Our estimates show that the effective energy migration from PBS to PSII is realized due to the existence of several transfer pathways from phycobilin chromophores of the PBS to the neighboring antennal chlorophyll molecules of the PSII. At the same time, the single binding site of photoactivated OCP and the PBS is sufficient to realize the quenching.