- The hybrid rat cytochrome P450 containing the first 5 exons of the CYP11B1 and last 4 exons from the CYP11B2 enzyme retains 11 beta-hydroxylase activity, but the alternative hybrid is inactive. Zhou, M.Y., Gomez-Sanchez, C.E., Xue, D., Foecking, M.F. Biochem. Biophys. Res. Commun. (1994)