Abstract
Energy-transfer processes in phycocyanin 612, a light-harvesting biliprotein from the cryptomonad alga Hemilselmis virescens, have been studied by picosecond fluorescence spectroscopy. Fluorescence was excited with a 30 ps 532 nm laser pulse and detected with a streak camera. Two types of data were obtained. Profiles of intensity versus time using 10 nm band pass interference filters are summarized as follows: emission at wavelengths <590 nm is characterized by a fast (7 to 11 ps) exponential decay; emission at longer wavelengths (> 650 nm) exhibits a 7 to 10 ps exponential rise time and a long exponential decay (1.0–1.4 ns). In the region from 600 to 640 nm, the time-resolved emission is more complicated; it consists of at least the sum of the shorter and longer wavelength components but additional components cannot be ruled out. The second type of data consists of spectra (intensity versus wavelength) taken at various times relative to the excitation pulse. These spectra qualitatively confirm the interference filter results. The kinetic results are interpreted in terms of Förster energy transfer between spectrally different chromophores within the biliprotein. Thus the emission of phycocyanin 612 provides a direct probe for studying the fast component of fluorescence during an energy transfer process.
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