Sauer, Kenneth; Scheer, Hugo
Excitation transfer in C-phycocyanin. Förster transfer rate and exciton calculations based on new crystal structure data for C-phycocyanins from Agmenellum quadruplicatum and Mastigocladus laminosus.
In: Biochimica et Biophysica Acta (BBA) - Bioenergetics, Vol. 936, Nr. 2: S. 157-170
Calculations of excitation transfer rates among the chromophores of C-phycocyanin using the Förster inductive resonance transfer mechanism have been carried out using the new coordinates for the position and orientation of the chromophores (Schirmer, T., Bode, W. and Huber, R. (1987) J. Mol. Biol. 196, 677–695). Several of the rate constants are significantly altered from the results of our calculations using the previously published coordinates (Sauer, K., Scheer, H. and Sauer, P. (1987) Photochem. Photobiol. 46, 427–440). In particular, for the (αβ)3-trimers of Mastigocladus laminosus or for the (αβ)3-trimers or the (αβ)6-hexamers of Agmenellum quadruplicatum, the new calculations predict excited state relaxation components with exponential time constants shorter than 1 ps. In fact, some of the interchromophore interactions are so strong that exciton coupling is probably the relevant mechanism of interaction. The largest exciton energy is calculated to be about 56 cm−1, for the interaction between the adjacent α84 and β84 chromophores of neighboring monomer units within the (αβ)3-trimers or (αβ)6-hexamers. An energy transfer model invoking a combination of pairwise exciton formation followed by slower Förster transfer steps is described.