Characterization of the biliproteins of Gloeobacter violaceus chromophore content of a cyanobacterial phycoerythrin carrying phycourobilin chromophore

The biliproteins of the unicellular, thylakoid-less cyanobacterium Gleobacter violaceus were resolved by chromatography on hydroxylapatite and DEAE-cellulose into five components: phycoerythrin I and II, phycocyanin I and II, and allophycocyanin. Allophycocyanin B was not detected. Three of these components, phycoerythrin II, phycocyanin II, and allophycocyanin, were purified to homogeneity. Phycoerythrin II crystallized as hexagonal prisms. G. violaceus allophycocyanin crystallized as thin plates; unter similar conditions other cyanobacterial allophycocyanins crystallize as needles. The biliproteins in the phycoerythrin I and phycocyanin I components were present in polydisperse, high molecular weight aggregates, which may represent incompletely dissociated substructures of the phycobilisome. Both phycoerythrin components from G. violaceus carry phycoerythrobilin and phycourbilin groups in the ratio of 6:1. Separation of the α and β subunits of these biliproteins revealed that the phycoerythrobilins were equally distributed between the two subunits, and that the β subunit alone carried the phycourobilin. These phycoerythrins are the first cyanobacterial phycobiliproteins found to carry a phycourobilin prosthetic group.