Energy Transfer in Trimeric C‐phycocyanin Studied by Picosecond Fluorescence Kinetics

Abstract

Abstract-The excited state kinetics of trimeric C-phycocyanin from Masrigocladus /arnirzosu.c. has been measured as a function of the emission and excitation wavelength by the single-photon timing technique with picosecond resolution and simultaneous data analysis. A last decay componcnt of 22 ps (C-phycocyanin with linker peptides) and 36 ps (C-phycocyanin lacking linker peptides) is attributed to efficient energy transfer from sensitizing to fluorcscing chromophores. At long dctcction wavelengths the fast decay components are found to turn into a rise t a m . This finding further corroborates thc concept o f intramolecular energy transfer. Previous reports on the conformational heterogeneity of the chromophores and/or proteins in C-phycocyanin are confirmcd. Our data also provide indications for the importancc of the uncoloured linker peptides for this hctcrogeneity.

Förster energy transfer between neighbouring chromophores in C-phycocyanin trimers

“…2, a fit with two exponentials with r = 0.37 ps and 30 ps would be in good agreement with the experimental curve. The 370-fs lifetime coincides with the calculated Forster transfer between a-84 and /3-84, while the 30-ps lifetime is similar to the picosecond absorption and fluorescence date reported previously [7][8][9][10][11][12][13]. The latter has been interpreted to be due to/3-155 transfer to a-84 (/3-84) [7][8][9] or as a relaxation between excitonic states [13].…”

“…The longer ps components found in both absorption and fluorescence studies of APC trimers were interpreted to be due to distortion of the APC trimer structure upon removal of the linker polypeptide [16]. The 20-30 ps component observed previously in C-PC trimers is, in our opinion, best explained by F6rster transfer from /3-155 to the a-84 and/3-84 chromophores [7][8][9][10][11][12]14]. A similar component was also observed in this work in both trimeric and monomeric preparations (Figs.…”

“…Initially, excited/3-155 chromophores are not expected to undergo energy transfer during the first few picoseconds [7][8][9][10][11][12], which is also corroborated by the lack of this component for C-PC monomers. The population of excited a-84 (donors) will change with time due to fast transfer of energy to/3-84 according to Eqn.…”

“…A 23-ps component in C-PC trimers was originally interpreted as energy transfer from the donor chromophore (/3-155) to /3-84 and ~-84 ones [7][8][9][10][11][12]. More recently, the same component was, however, suggested to play a part in a relaxation between two excitonic bands formed by an interaction between the closelysituated a-84 and /3-84 chromophores [13].…”

“…Previous absorption and fluorescence picosecond work on C-PC trimers has shown that the fastest energy transfer rates are in the order of 10-50 ps [7][8][9][10][11][12][13]. A 23-ps component in C-PC trimers was originally interpreted as energy transfer from the donor chromophore (/3-155) to /3-84 and ~-84 ones [7][8][9][10][11][12].…”