title: Characterization of a specific, high affinity binding macromolecule for 1 alpha, 25-dihydroxyvitamin D3 in cultured chick kidney cells.
abstract: Cytosol prepared from vitamin D3-deficient kidney cells in culture contains a 3.7 S protein that specifically binds 1,25-dihydroxyvitamin D3 with high affinity and low capacity. Whole kidney homogenate cytosol preparations are shown to possess two 1,25-dihydroxyvitamin D3 binding macromolecules. One of the binding proteins sediments at 3.5 to 3.7 S while the second sediments at 6.0 S. The 6.0 S component has a greater affinity for 25-dihydroxyvitamin D3 than for 1,25-dihydroxyvitamin D3. Cultured cell cytosol was found to have little 6.0 S 25-hydroxyvitamin D3 binding protein. Scatchard analysis of the cultured cell cytosol reveals an equilibrium binding constant (KD) of 5.6 x 10 (-11) with 57 fmol of sites/mg of protein. The receptor-like protein has a Mr = 72,000 and as with other steroid receptors it aggregates in the presence of low potassium concentrations. Analog competition for receptor binding reveals the following potency order: 1,25-dihydroxyvitamin D3 > 25-hydroxyvitamin D3 > 1 alpha-hydroxyvitamin D3 > 24(R),25-dihydroxyvitamin D3; the receptor had no detectable affinity for vitamin D3. The kidney cells respond to 1,25-dihydroxyvitamin D3 by diminishing 25-hydroxyvitamin D3 1 alpha-hydroxylation and increasing 24R-hydroxylation. Cultured cells provide a preparation of cytosol which has allowed extensive characterization of the renal 1,25-dihydroxyvitamin D3 receptor and should facilitate investigations into the role this receptor plays in renal control of vitamin D3 metabolism.
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002478:Cells, Cultured; D002645:Chickens; D003600:Cytosol / Q000378:metabolism; D007668:Kidney / Q000378:metabolism*; D007700:Kinetics; D008970:Molecular Weight; D018167:Receptors, Calcitriol; D011987:Receptors, Steroid / Q000302:isolation & purification / Q000378:metabolism*; D014808:Vitamin D Deficiency / Q000378:metabolism
chemical_list: D018167:Receptors, Calcitriol; D011987:Receptors, Steroid