COMPUTER-SIMULATION ON THE ENERGY-TRANSFER PROCESSES IN ALLOPHYCOCYANINS

The allophycocyanin core is situated between the photosynthetic reacti on center and the rods of a phycobilisome of algae and it accepts the excitation energy from the rods and then transfers the energy into the reaction center. Based on the crystal structure data and the spectra of the subunits in allophycocyanin, the energy transfer processes in t he monomer and trimer of allophycocyanin were studied by the computer simulation technique. It was learnt from the simulation that the energ y transfer kinetics between the two chromophores in an allophycocyanin monomer was very similar to that in a C-phycocyanin monomer, while th e energy transfer nature in an APC trimer was quite different from tha t in a C-PC trimer. In a C-phycocyanin trimer, the beta(84) chromophor es are the main fluorescent emitters, while the alpha(84) ones are the main fluorescent emitters in an APC trimer. This can be explained by their structure characteristics in phycobilisomes, that is, the basica l unit of C-phycocyanin in the rod of PBS is the hexamer while that of APC in the core of PBS is the trimer. The energy transfer from one tr imer to another is most likely through the alpha(84) chromophores, fro m which it can be further deduced that one APC trimer approaches anoth er in the face-to-face manner. The structural feature of APC is necess ary to realize the energy transfer function in high efficiency.