Abstract
The calbindins, calbindin-D9k and calbindin-D28k, belong to a family of high-affinity calcium-binding proteins characterized by the EF hand structural motif. Calbindin was the first identified target of vitamin D action. It is now known that the calbindins are not exclusively regulated by vitamin D. They are present in many different tissues, serve different functions, and are regulated by factors other than 1,25(OH)2D3. Calbindin-D28k is highly conserved in evolution. Calbindin-D9k, however, is present only in mammals. Evidence suggests that calbindin-D28k is involved in protection against apoptotic cell death by buffering calcium and by inhibiting caspase-3. Additional functions of calbindin include maintenance of intracellular calcium homeostasis and modulation of calcium influx.