Formation of raloxifene homo-dimer in CYP3A4, evidence for multi-substrate binding in a single catalytically competent P450 active site

► A raloxifene dimer metabolite was observed in CYP3A4 supersomeTM incubations. ► GSH products from HRP vs CYP3A4 suggested dimer was formed in the P450 active site. ► A dimer standard inhibited CYP3A4 activity towards 1' and 4 midazolam hydroxylase. ► Dimer formation was not affected by addition of ROS scavengers or trapping agents. ► Dimer formation was affected by addition of known CYP3A4 inhibitors/activators.