Picosecond Time-Resolved Polarized Emission Spectroscopy of Biliproteins (Influence of Temperature and Aggregation)

Abstract

Phycobiliproteins are photosynthetic light-harvesting pigments in blue-green and red algae. They consist of 2-3 polypeptide subunits, each bearing up to 4 covalently bound linear tetrapyrrolic chromophores. In vivo the biliproteins are organized into complex structures, the phycobilisomes, which are attached to the outer thylakoid surface. Within the phycobilisome the excitation energy is transfered from the "outer" biliproteins with higher excitation energy to "inner" lying ones with lower excitation energy. In the intact alga the last step in the ener gy transfer chain leads to the reaction center. It is generally assumed that the energy transfer is based upon dipole-dipoleinteraction (Forster mechanism), but details are yet insufficiently understood. In an approach complementary to the study of energy transfer in functionally intact phycobilisomes or large fractions thereof /1/ we are currently investigating by time-resolved fluorescence spectroscopy C-Phycocyanin (PC) isolated from Mastigocladus laminosus and its subunits, which are prepared according to procedures described earlier /2,3/. All samples are dissolved in potassium phosphate buffer (80 mM, pH 6.0).