Light-harvesting photosynthetic bile pigment-protein from the phycobiliprotein complex. Allophycocyanin has a maximum absorption at approximately 650 nanometers. Heterodimer of an alpha and a beta chain. Forms the core of the phycobilisome. Contains one covalently linked phycocyanobilin chromophore. Although originally identified as Cyanidium caldarium, these sequences derive from Galdieria sulphuraria. Belongs to the phycobiliprotein family.