Based on the crystal structure data from X-ray analysis,the energy transfer processes inthe 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 finallylost through fluorescence emission.(ii)The higher the aggregate,the less the transfer times.(iii)In atrimer,an m-(mediate)chromophore in a monomer and an f-(fluorescing)chromophore in another are inclosest proximity to each other and an appropriate orientation.These two chromophores form a fast transferpair with their energy transfer proceeding so fast that the time constant is less than 1 ps.There are 3 suchfast transfer pairs which are symmetrically equivalent in a trimer,while the paths of m■f and f■f betweenthe monomers are responsible for linking the fast transfer pairs.(iv)The excitation energy on an s-(sensi-tizing)chromophore is dominantly transferred to the f-chromophore in the same monomer.(v)In the hex-amer,there are 2 types of principal paths for linking the 2 trimers,which are m■m and s■s paths,whilethe excitation energy on the f-chromophores will be transferred into another trimer through the m-chro-mophore in the same fast transfer pair.The simulation shows that the hexamer possesses an optimal struc-ture for energy transfer.
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