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Journal of Clinical Endocrinology & Metabolism, Vol 43, 86-91, Copyright © 1976 by Endocrine Society

ARTICLES

Human serum binding capacity and affinity for 25-hydroxyergocalciferol and 25-hydroxycholecalciferol

JG Haddad, L Hillman and S Rojanasathit

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.




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Copyright © 1976 by The Endocrine Society