Excitation Energy Transfer in Intact CpcL-Phycobilisomes from Synechocystis sp. PCC 6803.

This work highlights spectroscopic studies performed on a CpcL-phycobilisome (CpcL-PBS) light-harvesting complex from cyanobacterium Synechocystis sp. PCC 6803 ΔAB strain. The CpcL-PBS antenna has the form of a single rod made up exclusively of phycocyanins (PCs), a structure that is much simpler compared to the better known and broadly studied CpcG-PBS that consists of a cylindrical core with a set of protruding PC rods. Steady-state and time-resolved fluorescence studies demonstrated that the CpcL-PBS antenna comprises two spectral forms of phycocyanobilin (PCB), one emitting at 650 nm and a second emitting at 670 nm. The latter one presumably serves as the so-called terminal energy emitter without allophycocyanin. Studies of excitation energy migration between those two PCB forms demonstrated that even small buffer alterations, commonly applied by spectroscopists to tweak buffers to be more friendly for a certain type of spectroscopy, may lead to very different experimental outcomes and, in consequence, to differences in models of excitation migration pathway in this antenna complex.