Fluorescence polarization of triple-chromophore complexes with energy transfer

The formula for the determination of a fluorescence polarization degree is derived for triple-chromophore complexes with energy transfer: P = (3B - 1 + 2A)/(3 + B + 4A). In this formula B = q(12) cos(2)(?(12)) + q(13) cos(2)(?(13)) + q(23) cos(2)(?(23)) and parameters A and q(ij) are dependent on the kinetic parameters of energy exchange and the chromophore spectroscopic parameters. The angle ?ij is the angle between the transition dipole moments of the i and j chromophores. The formula was tested for the particular case of the C-phycocyanin (C-PC) of the blue-green algae Agmenellum quadruplicatum, which contain three chromophores, α-84, β-84, and β155. Polarized spectra were calculated for both the emission and the excitation spectra of C-PC β subunits and monomers.