Once vitamin D3 (VD3) is released from vitamin D binding protein (GC, DBP), it translocates from the extracellular region to the ER membrane, becoming available for hydroxylation by the microsomal enzyme CYP2R1 (Shinkyo et al. 2004).
Shinkyo, R, Ohta, M, Sakaki, T, Kamakura, M, Inouye, K
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