Vitamin D 25- Hydroxylase is an enzyme involved in the cascade of reactions responsible for converting Vit. D into an active human form. This protein is a dimer with two surface and two interior active sites. Our picture highlights the two oxygen ring active sites (RED) in there respective domains. The oxygen rings bind to the heme iron groups (Royal Blue) which mediate electron transfer, critical for activating the Vitamin D. 
By Nicholas Lopes, Craig Conner, Lonnie Yu
