The cytochrome P450 proteins are monooxygenases that catalyze many reactions involved in drug metabolism and synthesis of cholesterol, steroids and other lipids. The CYP27B1 protein catalyzes the conversion of 25-hydroxyvitamin D3 (25(OH)D) to 1-α,25-dihydroxyvitamin D3 (1,25(OH)2D) and functions in calcium metabolism, normal bone growth, and tissue differentiation.
