Characterization of chlorophyll-protein complexes isolated from a Siphonous green alga, Bryopsis corticulans

Six chlorophyll-protein complexes are isolated from thylakoid membranes of Bryopsis corticulans by dodecyl-beta-D-maltoside polyacrylamide gel electrophoresis. Unlike that of higher plants, the 77 K fluorescence emission spectrum of the CP1 band, the PSI core complexes of B. corticulans, presents two peaks, one at 675 nm and the other at 715-717 nm. The emission peak at 715-717 nm is slightly higher than that at 675 nm in the CP1 band when excited at 438 or 540 nm. However, the peak at 715 nm is obviously lower than that at 675 nm when excited at 480 nm. The excitation spectra of CP1 demonstrate that the peak at 675 nm is mainly attributed to energy from Chl b while it is the energy from Chl a that plays an important role in exciting the peak at 715-717 nm. Siphonaxanthin is found to contribute to both the 675 nm and 715-717 nm peaks. We propose from the above results that chlorophyll a and siphonaxanthin are mainly responsible for the transfer of energy to the far-red region of PSI while it is Chl b that contributes most of the transfer of energy to the red region of PSI. The analysis of chlorophyll composition and spectral characteristics of LHCP1 and LHCP3 also indicate that higher content of Chl b and siphonaxanthin, mainly presented in LHCP1, the trimeric form of LHCII, are evolved by B. corticulans to absorb an appropriate amount of light energy so as to adapt to their natural habitats.