Energy transfer among the chromophores in phycocyanins measured by picosecond kinetics

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Abstract
Energy-transfer processes in the algal light-harvesting proteins, the phycocyanins, were studied by means of picosecond absorption spectroscopy. After excitation at 530 nm, the absorption at several wavelengths in the range 480-669 nm decayed with a short time constant (ps) and a long time constant (> 1 ns). For C-phycocyanin, energy transfer from the .beta. to the .alpha. subunits is interpreted as being a likely candidate for the short time constant; the long time constant probably is the excitation lifetime of the chromophore on the .alpha. subunits. The time constants for energy transfer in monomers, trimers and hexamers of C-phycocyanin extracted from a blue-green alga, Phormidium luridum, were measured as .apprx. 85, .apprx. 56 and .apprx. 32 ps, respectively. The corresponding time constant in the cryptomonad phycocyanin 645 from Chroomonas spp. was < 8 ps.