S100G (calbindin D9K) is a vitamin D-dependent calcium-binding protein. S100G, which is a cytosolic protein, is a member of a family of calcium-binding proteins that includes calmodulin, parvalbumin, troponin C, and S100 protein. In the intestine, S100G is vitamin D-dependent and its expression correlates with calcium transport activity. S100G may increase Ca2+ absorption by buffering Ca2+ in the cytoplasm and increase ATP-dependent Ca2+ transport in duodenal basolateral membrane vesicles.