ðɪs stˈɛp ɪz pɚfˈɔːɹmd baɪ ðə mˌaɪɾəkˈɑːndɹɪəl sˈaɪɾəkɹˌoʊm pˈiː fˈoːɹhˈʌndɹɪd fˈɪfti ˈɛnzaɪm sˈɛvəntˌiːn ˈælfəhaɪdɹˈɑːksɪlˌeɪz sˌiːwˌaɪpˈiː sˈɛvəntˌiːn ˈeɪ wˈʌn ðæt ɪz pɹˈɛzənt ɪnðɪ ɐdɹˈiːnəl ænd ɡˈɑːnædz.
This step is performed by the mitochondrial cytochrome P450 enzyme 17α-hydroxylase (CYP17A1)  that is present in the adrenal and gonads.