The function of CYP51A1 (cytochrome P450 family 51 subfamily A member 1, ENSG00000001630) is as follows. Sterol 14alpha-demethylase that plays a critical role in the cholesterol biosynthesis pathway, being cholesterol the major sterol component in mammalian membranes as well as a precursor for bile acid and steroid hormone synthesis (PubMed:20149798, PubMed:8619637, PubMed:9559662). Cytochrome P450 monooxygenase that catalyzes the three-step oxidative removal of the 14alpha-methyl group (C-32) of sterols such as lanosterol (lanosta-8,24-dien-3beta-ol) and 24,25- dihydrolanosterol (DHL) in the form of formate, and converts the sterols to 4,4-dimethyl-5alpha-cholesta-8,14,24-trien-3beta-ol and 4,4- dimethyl-8,14-cholestadien-3beta-ol, respectively, which are intermediates of cholesterol biosynthesis (PubMed:20149798, PubMed:8619637, PubMed:9559662). Can also demethylate substrates not intrinsic to mammals, such as eburicol (24-methylene-24,25- dihydrolanosterol), but at a lower rate than DHL (PubMed:9559662). {ECO:0000269|PubMed:20149798, ECO:0000269|PubMed:8619637, ECO:0000269|PubMed:9559662}.