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cytochrome P450 family 24, subfamily A, polypeptide 1, also called vitamin D(3) 24-hydroxylase Cytochrome P450 24A1 (CYP24A1, EC 1.14.15.16) is also called 1,25-dihydroxyvitamin D(3) 24-hydroxylase (24-OHase), vitamin D(3) 24-hydroxylase, or cytochrome P450-CC24. It catalyzes the NADPH-dependent 24-hydroxylation of calcidiol (25-hydroxyvitamin D(3)) and calcitriol (1-alpha,25-dihydroxyvitamin D(3) or 1,25(OH)2D3). CYP24A1 regulates vitamin D activity through its hydroxylation of calcitriol, the physiologically active vitamin D hormone, which controls gene-expression and signal-transduction processes associated with calcium homeostasis, cellular growth, and the maintenance of heart, muscle, immune, and skin function. CYP24A1 belongs to the large cytochrome P450 (P450, CYP) superfamily of heme-containing proteins that catalyze a variety of oxidative reactions of a large number of structurally different endogenous and exogenous compounds in organisms from all major domains of life. CYPs bind their diverse ligands in a buried, hydrophobic active site, which is accessed through a substrate access channel formed by two flexible helices and their connecting loop.
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