Regulates intra- and extracellular levels of inorganic pyrophosphate (PPi), probably functioning as PPi transporter. Expressed in heart, brain, liver, spleen, lung, muscle, and kidney of adult animals. Strongly expressed in the developing articular cartilage of joints in the shoulder, elbow, wrist, and digits of the embryo. Defects in Ankh are the cause of a generalized, progressive form of arthritis. In ank mice hydroxyapatite crystals develop in articular surfaces and synovial fluid leading to joint space narrowing, cartilage erosion, and formation of bony outgrowths or osteophytes that cause fusion and joint immobility and destruction. Belongs to the ANKH family.