25-Hydroxyvitamin D3 1-alpha-hydroxylase

25-Hydroxyvitamin D₃ 1-alpha-hydroxylase also known as cytochrome p450 27B1 or simply 1-alpha-hydroxylase is a cytochrome P450 enzyme that in humans is encoded by the CYP27B1 gene. VD3 1A hydroxylase is located in the proximal tubule of the kidney and a variety of other tissues, including skin, immune cells, and bone.