Computer simulation on the energy transfer processes in allophycocyanins

Abstract

The allophycocyanin core is situated between the photosynthetic reaction 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 the monomer and trimer of allophycocyanin were studied by the computer simulation technique. It was learnt from the simulation that the energy transfer kinetics between the two chromophores in an allophycocyanin monomer was very similar to that in a C-phycoeyanin monomer, while the energy transfer nature in an APC trimer was quite different from that in a C-PC trimer. In a C-phycocyanin trimer, the s84 chromophores are the main fluorescent emitters, while thea 84 ones are the main fluorescent emitters in an APC trimer. This can be explained by their structure characteristics in phycobilisomes, that is, the basical 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 trimer to another is most likely through thea 84 chromophores, from which it can be further deduced that one APC trimer approaches another in the face-to-face manner. The structural feature of APC is necessary to realize the energy transfer function in high efficiency.