25-Hydroxycholecalciferol, the Probable Metabolically Active Form of Vitamin D

Abstract

The isolation, identification, and chemical synthesis of 25-hydroxycholecalciferol have been achieved, with the synthesized product identical in all respects to the isolated material. Evidence has been presented that strongly suggests this compound is the metabolically active form of vitamin D. As compared to vitamin D₃, it is more active biologically in rats and chicks and acts much more rapidly to induce bone mobilization and intestinal transport of calcium. It also induces bone mobilization in vitro, whereas vitamin D₃ is either not, or only minimally, effective in culture. Finally, the nucleus, more probably the nuclear membrane, is the primary subcellular site of localization of 25-hydroxycholecalciferol.