Abstract
1,25-Dihydroxyvitamin D 3 [1,25-(OH) 2D 3] receptor was characterized after partial purification of thymus cytosol by ammonium sulfate fractionation. The 1,25-(OH) 2D 3 receptor sediments at 3.7S in 5–20% sucrose gradients. The binding of 1,25-(OH) 2D 3 in thymic cytosol was a saturable process with high affinity (Kd = 0.12−0.48 nM) at 4°C. Competition for 1,25-(OH) 2[ 3H]D 3 receptor by nonradioactive analogs demonstrated the affinities of these analogs to be in order; 1,25-(OH) 2D 3 = 1,24R,25-(OH) 3D 3 = 1,25S,26-(OH) 3D 3 = 1,25R,26-(OH) 3D 3 > 1,25-(OH) 2D 3-26,23 lactone > 25-OHD 3 > 23R,25-(OH) 2D 3 > 24R,25-(OH) 2D 3 > 23S,25-(OH) 2D 3 ⋙ 25-OHD 3-26,23 lactone. The receptor bound to DNA cellulose columns in low salt buffer and eluted as a single peak at 0.21 M KCl. These findings provide evidence that the thymus possesses a 1,25-(OH) 2D 3 receptor with properties indistinguishable from 1,25-(OH) 2D 3 receptors in other tissues.
Published Version
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