Two 7α‐hydroxylase enzymes in bile acid biosynthesis

The addition of a 7-hydroxyl group is an early and often rate-limiting step in the synthesis of bile acids. This reaction is catalysed by two cytochrome P450 enzymes known as cholesterol 7 alpha-hydroxylase and oxysterol 7 alpha-hydroxylase. cDNAs encoding these proteins have been isolated and used to define two evolutionarily conserved pathways that produce 7 alpha-hydroxylated bile acids.