The function of CYP39A1 (cytochrome P450 family 39 subfamily A member 1, Ensembl gene identifier ENSG00000146233) is as follows. A cytochrome P450 monooxygenase involved in neural cholesterol clearance through bile acid synthesis (PubMed:10748047, PubMed:25201972). Catalyzes 7-alpha hydroxylation of (24S)- hydroxycholesterol, a neural oxysterol that is metabolized to bile acids in the liver (PubMed:10748047, PubMed:25201972). 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-ferrihemoprotein reductase) (PubMed:10748047, PubMed:25201972). .