Phycoerythrins in phycobilisomes from the marine red alga Polysiphonia urceolata

Phycoerythrins (PE) in phycobilisomes from Polysiphonia urceolata were studied in this research. Dissociative products of phycobilisomes were analyzed by sucrose density gradient centrifugation and native-PAGE. At least three types of PEs were found in the dissociative products of phycobilisomes. According to their molecular weights, absorption spectra and subunit components, they should be PE hexamer containing γ1 subunit, PE hexamer containing γ2 subunit and PE monomer containing no γ subunit. PEs bigger than hexmer were also found in the dissociative products of phycobilisomes in 200 mM phosphate buffer when dissociated phycobilisomes were analyzed by sucrose density gradient centrifugation. PE trimers containing no γ subunits were also found in products of dissociated phycobilisomes in deionized water when dissociated phycobilisomes were analyzed by native-PAGE. This is the first time that pure PE hexamers containing γ2 subunits were isolated from P. urceolata. The PE monomers containing no γ subunits should come from PE trimers or hexamers containing no γ subunits in the “rod” of phycobilisomes. It can be concluded that there are three types of PEs in “rod” of phycobilisomes from P. urceolata: PE containing γ1 subunit, PE containing γ2 subunit and PE containing no γ subunit.