Heterododecamer of 6 alpha and 6 beta chains. The basic functional unit of phycobiliproteins is a ring-shaped hexamer formed from two back-to-back trimers contacting via the alpha chain subunits. The trimers are composed of alpha/beta subunit heterodimers arranged around a three-fold axis of symmetry. The phycoerythrins also contain a gamma subunit which is located in the center of the hexamer.