Light-harvesting photosynthetic bile pigment-protein from the phycobiliprotein complex. Allophycocyanin has a maximum absorption at approximately 650 nanometers (By similarity). Heterodimer of an alpha and a beta chain. Forms the core of the phycobilisome. Contains one covalently linked phycocyanobilin chromophore. The chromophore on position 81 is added by the phycocyanobilin lyase CpcUS. The measured mass is that of the protein without the N-terminal Met plus one covalently linked phycocyanobilin chromophore. Belongs to the phycobiliprotein family.