Once out of the lysosome, 25-hydroxyvitamin D (calcidiol, 25(OH)D) translocates to the mitochondion where it is made available to the mitochondrial membrane-resident protein CYP27B1 for further hydroxylation. The mechanism of mitochondrial targeting is unknown but may involve some kind of intracellular vitamin D binding protein (IDBP). IDBPs are related to the hsc-70 family of heat shock proteins and may function to localise vitamin D metabolites to specific areas. No human IDBP has yet been characterised (Radons 2016).
Radons, J
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