Further hydroxylation of calcidiol in kidney to form calcitriol Authored: Jassal, B, 2008-10-01 13:18:42 EC Number: 1.14.13.13 Edited: Jassal, B, 2008-05-19 12:57:01 Pubmed11856765 Pubmed12855575 Reactome Database ID Release 43209868 Reactome, http://www.reactome.org ReactomeREACT_13628 Reviewed: D'Eustachio, P, 2008-05-28 08:30:54 The second step in vitamin D3 activation requires further hydroxylation of 25-hydroxyvitamin D3 (calcidiol) to 1alpha-25-dihydroxyvitamin D3 (calcitriol). This conversion is mediated by 25-hydroxyvitamin D-1alpha hydroxylase (CYP27B1).