Phycocyanin hexamers and their associated linker polypeptides in phycobilisomes from the marine red alga Polysiphonia urceolata.

Pure phycocyanin (PC) hexamers from red algae were first prepared in this research. PC hexamers are helpful for studying the role and mechanism of PCs in energy transfer within phycobilisomes from red algae. The PC hexamers from Polysiphonia urceolata are stable at lower pH (pH 5.0-6.0) and their fluorescence emission peak has a red shift of about 5 nm. A 27 kDa linker polypeptide associated with PC hexamers was found and it should be linker between PC and allophycocyanin (AP) and may be located in the central cavity of a PC hexamer and the side gap of two AP trimer discs. The 27 kDa linker polypeptides also may be linkers between APs and phycoerythrins (PE). PC hexamers can help us to study the lateral ways of energy transfer from PEs to PCs, and the study of polypeptides associated with PC hexamers also can provide more direct evidences or amendments to fine the structures of phycobilisomes from red algae (e.g. ascertaining the linkage between PC hexamers and their adjacent phycobiliproteins). Further studies on the AP fractions of this research may be helpful for researches on fine stucture of the core of phycobilisomes from red algae.