NPT2a — The Key to Phosphate Homeostasis

Phosphate leads two lives — an ancient intracellular one and a more recent extracellular one. Inside cells, phosphate has a structural role in nucleic acids and phospholipids, forms high-energy ester bonds (e.g., in adenosine triphosphate and guanosine triphosphate), and participates in cellular signaling through covalent phosphorylation of proteins and lipids. Outside cells, in animals with bones, the role of phosphate is quite different. Most extracellular phosphate is found in bone mineral. Because the concentrations of ionic calcium and phosphate in extracellular fluid are at, or exceed, their solubility product constant, elaborate controls have been developed to keep calcium–phosphate from precipitating . . .