25-Hydroxyvitamin D3 1-alpha-hydroxylase
（重定向自CYP27B1）
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25-Hydroxyvitamin D3 1-alpha-hydroxylase (VD3 1A hydroxylase) also known as cytochrome p450 27B1 (CYP27B1) 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 (keratinocytes), immune cells, and bone (osteoblasts). The enzyme catalyzes the hydroxylation of Calcifediol to calcitriol (the bioactive form of Vitamin D):