Comparison of the rate constants for energy transfer in the light-harvesting protein, C-phycocyanin, calculated from Forster's theory and experimentally measured by time-resolved fluorescence spectroscopy

e have measured and assigned rate constants for energy transfer between chromophores in the light-harvesting protein C-phycocyanin (PC), in the monomeric and trimeric aggregation states, isolated from Synechococcus sp. PCC 7002. In order to compare the measured rate constants with those predicted by Forster's theory of inductive resonance in the weak coupling limit, we have experimentally resolved several properties of the three chromophore types ;The individual fluorescence spectra of the chromophores and the rate constants for energy transfer between them in monomeric PC were resolved by time-resolved fluorescence measurements. We assign the observed 52 ps and 149 ps fluorescence decay constants to the inverse of the summed rate constants for forward and back energy transfer between the ;Time-resolved fluorescence anisotropy measurements by the fluorescence upconversion technique on PC trimers isolated from the wild-type and cpcB/C155S mutant strains lead to assignments of the dominant rate constants for energy transfer in PC trimers. The observed fluorescence decay times of 1.0 ps, 50 ps, and 40 ps are respectively assigned to energy transfer within the...