Light-harvesting photosynthetic bile pigment-protein from the phycobiliprotein complex. Allophycocyanin has a maximum absorption at approximately 650 nanometers. Component of the phycobilisome. Heterodimer of an alpha and a beta chain. Forms the core of the phycobilisome. Contains one covalently linked phycocyanobilin chromophore. Belongs to the phycobiliprotein family.