A rod-linker-contained R-phycoerythrin complex from the intact phycobilisome of the marine red alga Polysiphonia urceolata

A linker-contained R-phycoerythrin (R-PE) complex was obtained by the Sephadex G-150 column chromatography from the Polysiphonia urceolata phycobilisome (PBS) that was disassociated at 37 °C for 6 h in the dilute phosphate buffer (pH 7.0) with 5% (m/v) sodium dodecyl sulfate (SDS). The R-PE complex showed three absorption peaks at 498, 538 and 567 nm, and a fluorescence emission maximum at 578 nm. Polypeptide analysis of the complex by the 8–25% (m/v) gradient SDS–polyacrylamide gel electrophoresis demonstrated that it contained three red subunits, α PE 17.6 , β PE 19.2 and γ PE 31.0 , and a colorless 35.3 kDa rod-linker L R 35.3 . Polypeptide proportion of the complex demonstrated that it was a hexamer in aggregate form γ PE 31.6 α PE 17.6 β PE 19.2 3 L R 35.3 α PE 17.6 β PE 19.2 3 γ PE 31.6 which is proposed to originate from a rod assembly of hexamer–linker–hexamer the substructure α PE 17.6 β PE 19.2 3 of which was decomposed off from the ends of the assembly during the PBS dissociation. The distinctive stability of the prepared hexamer is attributed to a large extent to the electrostatic interaction among its polypeptides, but not to the hydrophobic interaction.