Cholecalciferol 25-hydroxylase
Vitamin D 25-hydroxylase also known as cytochrome P450 2R1 is an enzyme that in humans is encoded by the CYP2R1 gene.
Vitamin D 25-hydroxylase is a member of the superfamily of enzymes. The cytochrome P450 proteins are monooxygenases which catalyze many reactions involved in drug metabolism and synthesis of cholesterol, steroids and other lipids. Found in the liver, this enzyme is a microsomal vitamin D hydroxylase that converts vitamin D into 25-hydroxyvitamin D (calcidiol), which is the major circulatory form of the vitamin.
An inherited mutation in the CYP2R1 gene which results in the substitution of a proline for a leucine residue at codon 99 eliminates the enzyme activity and is associated with low circulating levels of 25-hydroxyvitamin D and classic symptoms of vitamin D deficiency. The gene product which it encodes, vitamin D 25-hydroxylase, has therefore been proposed as the key enzyme in the conversion of cholecalciferol (vitamin D3) to calcidiol. Calcidiol is subsequently converted by the action of 25-hydroxyvitamin D3 1-alpha-hydroxylase to calcitriol, the active form of vitamin D3 that binds to the vitamin D receptor (VDR) which mediates most of the physiological actions of the vitamin.
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