Orientation of optical transitions of pigments in isolated photosystem I particles

In order to obtain information about the orientation of the photosynthetic pigments in respect to the membrane and their mutual orientation in photosystem I (PS I) particles, a new formula for the fluorescence anisotropy at low temperatures in oriented complexes is derived. The calculation are based on the consideration of PS I complex as a oriented triple-chromophore complex with energy transfer under steady-state excitation. Assuming perfect orientation of the complexes, a dependence of the fluorescence anisotropy on the polarization of the linearly polarized exciting light is obtained. Based on the derived formula both the orientation of the absorbing photosynthetic pigments in respect to the membrane and their mutual orientation can be determined using steady state polarized fluorescence spectroscopy with a different polarization of the linearly polarized exciting light.