Involved in the metabolism of vitamin D3 (calciol) and of a number of sulfonylurea herbicides. Catalyzes the two-step hydroxylation (25- and 1-alpha-hydroxylation) of vitamin D3 (VD3) to yield its active form 1-alpha,25-dihydroxyvitamin D3 (calcitriol). The first step is the hydroxylation of the C-25 position of VD3 to produce 25-hydroxyvitamin D3 (calcidiol). The second reaction is the hydroxylation of the C1-alpha-position of calcidiol to produce calcitriol. It can also hydroxylate vitamin D2. calciol + 2 H(+) + O2 + 2 reduced [2Fe-2S]-[ferredoxin] = calcidiol + H2O + 2 oxidized [2Fe-2S]-[ferredoxin] calcidiol + 2 H(+) + O2 + 2 reduced [2Fe-2S]-[ferredoxin] = calcitriol + H2O + 2 oxidized [2Fe-2S]-[ferredoxin] kcat is 0.0076 min(-1) for hydroxylase activity with 1-alpha-hydroxyvitamin D3 as substrate. kcat is 0.0026 min(-1) for hydroxylase activity with 25-hydroxyvitamin D3 as substrate. By herbicides. Two metabolic pathways exist. One is a conversion of VD3 to 25-hydroxyvitamin D3 and then to 1-alpha,25-dihydroxyvitamin D3 (25-pathway), while the other one is a pathway via 1-alpha-hydroxyvitamin D3 as an intermediate (1-alpha-pathway). Analysis show that the amount of 25-hydroxyvitamin D3 is predominant as the product of this reaction, while very small amounts of 1-alpha-hydroxyvitamin D3 and 1-alpha,25-dihydroxyvitamin D3 are obtained, suggesting that the major pathway is the 25-pathway. The hydrophobicity and the volume of the side chain at position 84 are critical for the activity. Belongs to the cytochrome P450 family.