Competition by 24,25-dihydroxycholecalciferol in the competitive protein binding radioassay of 25-hydroxycalciferol.
24,25-dihydroxycholecalciferol (24,25-(OH)2D3) is equipotent to 25-hydroxycholecalciferol in the displacement of 3H25-OHD3 from rat serum binding sites, and is extracted by the ethanol procedure recommended in non-chromatographic competitive protein binding radioassays for 25-OHD. Serum 24,25-(OH)2D content was measured following 24,25-(OH)2D3 isolation from lipid extracts by liquid-gel partition chromatography. Since normal serum 24,25-(OH)2D concentration is appreciable, non-chromatographic 25-OHD assays most probably overestimate serum 25-OHD levels as a result of their recognition of 24,25-(OH)2D3.
D000818:Animals; D001667:Binding, Competitive; D004100:Dihydroxycholecalciferols / Q000097:blood*; D006801:Humans; D006887:Hydroxycholecalciferols / Q000097:blood*; D007700:Kinetics; D008832:Microchemistry; D011485:Protein Binding; D011869:Radioligand Assay / Q000379:methods; D051381:Rats; D011955:Receptors, Drug; D013329:Structure-Activity Relationship
D004100:Dihydroxycholecalciferols; D006887:Hydroxycholecalciferols; D011955:Receptors, Drug