Phycoerythrin-phycocyanin aggregates and phycoerythrin aggregates from phycobilisomes of the marine red alga Polysiphonia urceolata.

Phycoerythrin-phycocyanin aggregates and phycoerythrin aggregates showing special spectral characteristics were prepared from the partly dissociated products of phycobilisomes from Polysiphonia urceolata. The absorption difference spectra between the aggregates and phycoerythrins showing normal spectral characteristics show peaks at 583 nm. The fluorescence emission difference spectra between the phycoerythrin aggregates and normal phycoerythrins show peaks at 602 nm. The special spectral characteristics of the PE aggregates disappeared when the PE aggregates were dissociated in deionized water. The intact phycobilisomes show similar characteristics as phycoerythrin-phycocyanin aggregates. When the peak values at 583 nm in absorption difference spectra were compared with those at 615 nm, it can be found that the amount of the 583 nm chromophores in the phycoerythrin-phycocyanin aggregates and intact phycobilisomes is similar to the amount of PCB chromophores in phycocyanins. It can be concluded that the 583 nm chromophores are at the interface between phycoerythrins and phycocyanins in phycobilisomes and transfer the light energy absorbed by other chromophores in phycoerythrins to the PCB chromophores in phycocyanins. A rod linker polypeptide with molecular weight of 40 kDa was found in the phycoerythrin-phycocyanin aggregates and phycoerythrin aggregates, and it is believed to play roles in the spectral red shift of the aggregates.