Its precise biological substrate is not known. Catalyzes C14-demethylation of lanosterol, 24,25-dihydrolanosterol and obtusifoliol which is critical for ergosterol biosynthesis. It transforms lanosterol into 4,4'-dimethyl cholesta-8,14,24-triene-3-beta-ol. a 14alpha-methyl steroid + 3 O2 + 3 reduced [NADPH--hemoprotein reductase] = a Delta(14) steroid + formate + 4 H(+) + 4 H2O + 3 oxidized [NADPH--hemoprotein reductase] lanosterol + 3 O2 + 3 reduced [NADPH--hemoprotein reductase] = 4,4-dimethyl-5alpha-cholesta-8,14,24-trien-3beta-ol + formate + 4 H(+) + 4 H2O + 3 oxidized [NADPH--hemoprotein reductase] 24,25-dihydrolanosterol + 3 O2 + 3 reduced [NADPH--hemoprotein reductase] = 4,4-dimethyl-8,14-cholestadien-3beta-ol + formate + 4 H(+) + 4 H2O + 3 oxidized [NADPH--hemoprotein reductase] 3 O2 + obtusifoliol + 3 reduced [NADPH--hemoprotein reductase] = 4alpha-methyl-5alpha-ergosta-8,14,24(28)-trien-3beta-ol + formate + 4 H(+) + 4 H2O + 3 oxidized [NADPH--hemoprotein reductase] Inhibited by alpha-ethyl-N-4-pyridinyl-benzeneacetamide (EPBA) and 4,4'-dihydroxybenzophenone (DHBP). Steroid biosynthesis; zymosterol biosynthesis; zymosterol from lanosterol: step 1/6. Homodimer. Belongs to the cytochrome P450 family.