- Xenobiotic induction of cytochrome P450 2B1 (CYP2B1) is mediated by the orphan nuclear receptor constitutive androstane receptor (CAR) and requires steroid co-activator 1 (SRC-1) and the transcription factor Sp1. Muangmoonchai, R., Smirlis, D., Wong, S.C., Edwards, M., Phillips, I.R., Shephard, E.A. Biochem. J. (2001)