title: Dissociation of specific binding of 25-OH-D3 and resorption in fetal rat bones.
abstract: Specific binding of 25-OH-D 3 was measured in cytosol prepared from isolated fetal rat bone cells. Binding was significant after 2 h incubation at 0 degrees C and appeared to be approaching a plateau at 4 h. Binding was half-maximal at 1.7 X 10(-10) M 25-OH-D3. 24(R),25-(OH)2D3, which was approximately equipotent with 25-OH-D3 in bone culture, had approximately the same binding activity. 1,25-(OH)2D3, which was 2--3 orders of magnitude more active on resorption, was a much weaker competitor for binding. Vitamin D3, which was inactive in culture, was at least as effective a competitor as 1,25-(OH)2D3. The results suggest that the cytosol site which specifically bind 25-OH-D3 is not the mediator of the bone-resorbing activity.
mesh_terms: D000818:Animals; D001665:Binding Sites; D001862:Bone Resorption; D001842:Bone and Bones / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002762:Cholecalciferol / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D005260:Female; D005333:Fetus / Q000378:metabolism*; D006887:Hydroxycholecalciferols / Q000378:metabolism*; D011247:Pregnancy; D051381:Rats
chemical_list: D006887:Hydroxycholecalciferols; D002762:Cholecalciferol; D002118:Calcium