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1α,25(OH)2D3 Dependent Calcium Binding Proteins

المؤلف:  Norman, A. W., & Henry, H. L.

المصدر:  Hormones

الجزء والصفحة:  3rd edition , p208-209

2026-08-03

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Three distinct 1α,25(OH)2D3-induced calcium-binding proteins have been isolated and biochemically characterized. These proteins are all produced de novo as a consequence of the 1,25(OH)2D3 VDR receptor com plex that has stimulated selective gene activation. The two proteins which tightly bind Ca2+ with a Kd of 10⁻⁷ M are termed calbindins [the 9 kDa CaBP (mammals) and the 28-kDa (birds) CaBP], and belong to a family of tight calcium-binding proteins; other members of this family include the muscle proteins troponin C and parvalbumin and the widely distributed calmodulin. All of these proteins are known to have a high degree of structural similarity in their calcium-binding sites. The third vitamin D-induced calcium-binding protein is osteocalcin; it is an osteoblast secreted extracellular protein associated with bone matrix. It is sometimes referred to as the bone Gla protein (BGP), since it has many γ-carboxyglutamic acid residues that bind Ca2+ with a Kd of only ~1×10⁻³ M. Osteocalcin is the fifth most abundant protein in the body.