COMPUTER-SIMULATION ON KINETICS OF PRIMARY PROCESS IN PHOTOSYNTHESIS(III)

Based on the crystal structure data from X-ray analysis, the energy transfer processes in the trimers and hexamers of C-phycocyanins (C-PC) have been simulated. The simulation results show (i) The excitation energy could transfer back and forth many times through a certain path before it was finally lost through fluorescence emission. (ii) The higher the aggregate, the less the transfer times. (iii) In a trimer; an m- (mediate) chromophore in a monomer and an f- (fluorescing) chromophore in another are in closest proximity to each other and an appropriate orientation. These two chromophores form a fast transfer pair with their energy transfer proceeding so fast that the time constant is less than 1 ps. There are 3 such fast transfer pairs which are symmetrically equivalent in a trimer, while the paths of m <----> f and f <----> f between the monomers are responsible for linking the fast transfer. pairs. (iv) The excitation energy on an s- (sensitizing) chromophore is dominantly transferred to the f-chromophore in the same monomer. (v) In the hexamer, there are 2 types of principal paths for linking the 2 trimers, which are m <----> m and s <----> s paths, while the excitation energy on the f-chromophores will be transferred into another trimer through the m-chromophore in the same fast transfer pair. The simulation shows that the hexamer possesses an optimal structure for energy transfer.