25-Hydroxycholecalciferol-binding protein: Partial purification from rat duodenal mucosa cells

The 25-hydroxycholecalciferol-binding protein has been partially purified (purification factor: 37) from rat duodenal cytosol, using chromatographic procedures on gel and ionic exchange resin. This partially purified protein bound 25-hydroxycholecalciferol with high affinity (K_D = 5.7 × 10^?9M) and low binding capacity (23 × 10^?12 mole/mg of protein. Using a rabbit antiserum obtained against such partially purified protein, we demonstrated that 25-hydroxycholecalciferol cytosolic binder and 25-hydroxycholecalciferol plasmatic binding share common antigenic sites.