A mitochondrial cytochrome P450 enzyme that catalyzes the 11-beta-hydroxylation of steroids in the presence of molecular oxygen and nadph-ferrihemoprotein reductase. This enzyme, encoded by CYP11B1 gene, is important in the synthesis of corticosterone and hydrocortisone. Defects in CYP11B1 cause congenital adrenal hyperplasia (adrenal hyperplasia, congenital).