Studies on the energy transfer among the rod-core complex from phycobilisome of Anabaena variabilis by time resolved fluorescence emission and anisotropy spectra

Abstract

Picosecond time-resolved fluorescence emission and polarization spectra were recorded for the rod-core complex ( α β) 6 PCL RC 27( α β) 3 APL C 8.9 from cyanobacterium Anabaena variablis. Fluorescence decay was measured by single-photon timing and resolved to kinetic components by global data analysis with two different excitation wavelengths at 580 nm and 640 nm. Fluorescence anisotropies were recorded and analyzed at different excitation/emission pairs, such as, 590 nm/625 nm, 625 nm/640 nm, 635 nm/652 nm and 650 nm/665 nm. It was expected through this work to investigate the energy transfer processes between C-PC and APC, as well as those in a C-PC hexamer. Our data indicated that the rod-core complex acted as a functional entity with respect to excitation energy transfer. The kinetic component of 18 ps, observed with excitation at 580 nm and 640 nm, was interpreted as the excitation energy transfer from the three β 84 chromophores of terminal C-PC trimer to an α 84 chromophore in the APC core. The 55 ps component, observed with excitation at 580 nm, most likely represent the transfer from β 155-PCB to β 84-PCB in a C-PC monomer. The component of 110 ps, observed with excitation at 640 nm, may originate from the transfer between α 84- and β 84-PCB chromophores in a APC monomer. The 10 ps component was assigned to the energy transfer processes between the identical β 155-PCB or α 84-PCB chromophores in two trimers while the 40±2 ps and 45 ps components to those among the three β 84-PCB chromophores in a C-PC trimer and an APC trimer, respectively.