Some characteristics of cytosol binding protein for 1alpha,25-dihydroxycholecalciferol and 25-hydroxycholecalciferol in rat intestinal mucosa.
Cytosol binding protein for 1alpha,25-(OH)2D3 and 25-OHD3 was demonstrated in rat intestinal mucosa using sucrose density gradient ultracentrifugation analysis, Sephadex G-200 column chromatography and polyacrylamide disc gel electrophoresis. The binding protein has a sedimentation constant of 5-6S, a molecular weight of 100,000-120,000 daltons and a mobility in electrophoresis of Rf 0.42. Further analysis of binding behavior by DEAE-cellulose filter assays revealed that the bindig protein had a higher affinity for 25-OHD3 than for 1alpha,25-(OH)2D3, and that 1alpha,25-(OH)2D3 competed with 25-OHD3 for the same binding site on the protein. The apparent dissociation constant for 1alpha,25-(OH)2D3 and 25-OHD3 was 9.2 X 10(-9) M and 1.5 X 10(-9) M, respectively. The binding capacity was 3.1 pmoles/mg protein for both 1alpha,25-(OH)2D3 and 25-OHD3. The order of binding affinity was 25-OHD3 greater than 1alpha,25-(OH)2D3 greater than D3 = 1alpha-OHD3.
D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004100:Dihydroxycholecalciferols / Q000378:metabolism*; D006887:Hydroxycholecalciferols / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000378:metabolism*; D008297:Male; D051381:Rats; D013329:Structure-Activity Relationship; D014808:Vitamin D Deficiency / Q000378:metabolism
D002352:Carrier Proteins; D004100:Dihydroxycholecalciferols; D006887:Hydroxycholecalciferols