Physiology and biochemistry of vitamin D-dependent calcium binding proteins

The vitamin D-de-pendent calcium binding proteins (calbindins) are members of the troponin-C superfamily of proteins that occur in a number of calcium-transporting tissues such as the intestine, the distal tubule of the kidney, and the placenta. They are also present in other tissues such as the brain, peripheral nervous system, pancreas, parathyroid gland, and bone. In some tissues, such as the adult brain, the proteins occur in the absence of the vitamin. The proteins bind calcium in "EF" hand structures and are "calciumsensitive" in that they undergo a conformational change on binding calcium. They appear to enhance transcellular calcium transport and are frequently present in tissues that contain the plasma membrane calcium pump.