Steady-state and femtosecond time-resolved optical methods have been used to study spectroscopic features and energy transfer dynamics in the soluble antenna protein phycocyanin 645 (PC645), isolated from a unicellular cryptophyte Chroomonas CCMP270. Absorption, emission and polarization measurements as well as one-colour pump–probe traces are reported in combination with complementary quantum chemical calculations of electronic transitions of the bilins. Estimation of bilin spectral positions and energy transfer rates aids in the development of a model for light harvesting by PC645. At higher photon energies light is absorbed by the centrally located dimer (DBV, b50/b61) and the excitation is subsequently funneled through a complex interference of pathways to four peripheral pigments (MBV a19, PCB b158). Those chromophores transfer the excitation energy to the red-most bilins (PCB b82). We suggest that the final resonance energy transfer step occurs between the PCB 82 bilins on a timescale estimated to be ∼15 ps. Such a rapid final energy transfer step cannot be rationalized by calculations that combine experimental parameters and quantum chemical calculations, which predict the energy transfer time to be 40 ps.
Ultrafast light harvesting dynamics in the cryptophyte phycocyanin 645
MENNUCCI, BENEDETTA;
2007-01-01
Abstract
Steady-state and femtosecond time-resolved optical methods have been used to study spectroscopic features and energy transfer dynamics in the soluble antenna protein phycocyanin 645 (PC645), isolated from a unicellular cryptophyte Chroomonas CCMP270. Absorption, emission and polarization measurements as well as one-colour pump–probe traces are reported in combination with complementary quantum chemical calculations of electronic transitions of the bilins. Estimation of bilin spectral positions and energy transfer rates aids in the development of a model for light harvesting by PC645. At higher photon energies light is absorbed by the centrally located dimer (DBV, b50/b61) and the excitation is subsequently funneled through a complex interference of pathways to four peripheral pigments (MBV a19, PCB b158). Those chromophores transfer the excitation energy to the red-most bilins (PCB b82). We suggest that the final resonance energy transfer step occurs between the PCB 82 bilins on a timescale estimated to be ∼15 ps. Such a rapid final energy transfer step cannot be rationalized by calculations that combine experimental parameters and quantum chemical calculations, which predict the energy transfer time to be 40 ps.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
