Binding of 25-hydroxycholecalciferol in tissues.
Evidence is presented that the 5.8 S 25-hydroxycholecalciferol-binding protein found in the cytosols of all nucleated rat tissues is formed from two macromolecular substances: a heat-stable 4.1 S 25-hydroxycholecalciferol-binding protein which behaves identically with the serum 25-hydroxycholecalciferol-binding protein, and a cytosolic heat-labile protein which appears to sediment around 4 S and does not show binding properties for 25-hydroxycholecalciferol. The 5.8 S complex is formed in vitro by incubating cytosols with appropriate amounts of serum. The complex is dissociated by heating, leaving the serum 25-hydroxycholecalciferol-binding protein. Complex formation also occurred with serum 25-hydroxycholecalciferol-binding proteins from other species. The widespread occurrence of the 4 S cytosolic component raises the possibility that the high affinity binding proteins for 25-hydroxycholecalciferol observed in nucleated tissues are largely the result of plasma contamination.
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism; D006887:Hydroxycholecalciferols / Q000097:blood / Q000378:metabolism*; D007668:Kidney / Q000378:metabolism; D009132:Muscles / Q000378:metabolism; D009928:Organ Specificity; D051381:Rats; D012260:Ribonucleases; D014357:Trypsin
D002352:Carrier Proteins; D006887:Hydroxycholecalciferols; D012260:Ribonucleases; D014357:Trypsin