A cytochrome P450 monooxygenase involved in primary bile acid biosynthesis. Catalyzes the 12alpha-hydroxylation of 7alpha-hydroxy-4-cholesten-3-one, an intermediate metabolite in cholic acid biosynthesis (By similarity). Controls biliary balance of cholic acid and chenodeoxycholic acid, ultimately regulating the intestinal absorption of dietary lipids (PubMed:12393855, PubMed:28377401). Mechanistically, uses molecular oxygen inserting one oxygen atom into a substrate, and reducing the second into a water molecule, with two electrons provided by NADPH via cytochrome P450 reductase (CPR; NADPH--hemoprotein reductase) (By similarity). 7alpha-hydroxycholest-4-en-3-one + O2 + reduced [NADPH--hemoprotein reductase] = 7alpha,12alpha-dihydroxycholest-4-en-3-one + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] 5beta-cholestane-3alpha,7alpha-diol + O2 + reduced [NADPH--hemoprotein reductase] = 5beta-cholestane-3alpha,7alpha,12alpha-triol + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] chenodeoxycholate + O2 + reduced [NADPH--hemoprotein reductase] = cholate + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] Lipid metabolism; bile acid biosynthesis. Expressed in liver. By cholestyramine treatment (PubMed:10051404). Induced upon starvation (PubMed:10051404). Knockout mice are resistant to Western diet-induced hepatic steatosis due to impaired cholic acid synthesis and deficient fat absorption. Belongs to the cytochrome P450 family.