Promotes endocytosis, possesses opsonic properties and influences the mineral phase of bone. Shows affinity for calcium and barium ions (By similarity). Alpha-2-HS glycoprotein derives from this precursor, when the connecting peptide is cleaved off. The two chains A and B are held together by a single disulfide bond (By similarity). Phosphorylated by FAM20C in the extracellular medium. Belongs to the fetuin family.