Catalytic activity:Calcidiol + NADPH + O(2) = secalciferol + NADP(+) + H(2)O.,Catalytic activity:Calcitriol + NADPH + O(2) = calcitetrol + NADP(+) + H(2)O.,cofactor:Heme group.,Function:Has a role in maintaining calcium homeostasis. Catalyzes the NADPH-dependent 24-hydroxylation of calcidiol (25-hydroxyvitamin D(3)) and calcitriol (1-alpha,25-dihydroxyvitamin D(3)). The enzyme can perform up to 6 rounds of hydroxylation of calcitriol leading to calcitroic acid. It also shows 23-hydroxylating activity leading to 1-alpha,25-dihydroxyvitamin D(3)-26,23-lactone as end product.,similarity:Belongs to the cytochrome P450 family.,
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