title: Human serum binding capacity and affinity for 25-hydroxyergocalciferol and 25-hydroxycholecalciferol.
abstract: 25-Hydroxyvitamin D-binding capacity and affinity were studied in human cord, adult, and maternal sera, and in sera from women receiving oral contraceptives, by in vitro satuaration analyses employing dextran-coated charcoal to adsorb unbound sterol. 25-Hydroxyergocalciferol and 25-hydroxycholecalciferol were equipotent in their ability to displace 3H 25-hydroxycholecalciferol from human serum binding sites. At 0C, the apparent dissociation constant for the serum binding of 25-hydroxycholecalciferol was low (Kd=8x 10-10M). Cord and adult sera had a similar 25-hydroxycholecalciferol binding capacity (1.8 x 10-6M), but the binding capacity of maternal sera and the sera from women receiving oral contraceptives was significantly higher. At physiological serum concentrations of 25-hydroxyvitamin D (5 x 10-8M), only 2-3% of human serum 25-hydroxyvitamin D-bindig sites are occupied.
mesh_terms: D000328:Adult; D001665:Binding Sites; D001798:Blood Proteins / Q000378:metabolism*; D003276:Contraceptives, Oral / Q000494:pharmacology; D004872:Ergocalciferols / Q000097:blood*; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D006801:Humans; D006887:Hydroxycholecalciferols / Q000097:blood*; D008297:Male; D011247:Pregnancy; D011374:Progesterone / Q000494:pharmacology
chemical_list: D001798:Blood Proteins; D003276:Contraceptives, Oral; D004872:Ergocalciferols; D006887:Hydroxycholecalciferols; D011374:Progesterone; D004958:Estradiol