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Calcidiol

25-hydroxycholecalciferol (a 3,25-diol);the first step in the biological conversion of vitamin D3 to the more active form, calcitriol; it is more potent than vitamin D3.

Synonym: 25-hydroxycholecalciferol, calcifediol.

calcidiol 1a-hydroxylase, 25-hydroxycholecalciferol 1a-hydroxylase, the monooxygenase that forms calcitriol from calcidiol using O2 and NADPH; a deficiency in this enzyme can result in features of a vitamin d deficiency.