Vitamin D metabolism

Pro-Vit.D--> Vit.D3 (in skin with UV light)
Vit.D3--> 25-0H (in liver)
25-OH--> 1,25 (0H)2 (in kidneys)
http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/otherendo/vitamind.html