CYP8B1 (sterol 12-alpha-hydroxylase) is a member of the cytochrome P450 superfamily of monooxygenase enzymes that are involved in the metabolism of a wide array of endogenous and xenobiotic compounds. CYP8B1 is highly expressed in liver and is an important enzyme for bile acid synthesis. Specifically, CYP8B1 moderates the ratio of cholic acid over chenodeoxycholic acid to control the solubility of cholesterol. The gene encoding human CYP8B1 maps to chromosome 3p22.1. The CYP8B1 gene encodes a 501-amino acid protein and does not contain any introns. The CYP8B1 gene promoter is transactivated by hepatocyte nuclear factor 4a. In mice, disruption of the CYP8B1 gene prevents the synthesis of cholate, which is a primary bile acid.