A filamentous freshwater cyanobacteriuni, identifíed as Oscillatoria annae, has two different phycoerythrins. One of them contains only phycoerythrobilin chromophores, thus being a typical C-phycoerythrin. The other has both phycoerythrobilin and phycourobilin chromophores and is therefore related to CU- phycoerythrins (cyanobacterial phycoerythrins containing urobilin). The stoichiometry of the chromophore prosthetic groups in CU-phycoerythrin from O. annae is 1:1, therefore the (ap)-polypeptide monomer of this phycoerythrin carries three phycoerythrobilin and three phycourobilin prosthetic groups. The pigment is believed to be a new t3T)e of CU-phycoerythrin.