Catalyzes the 14-alpha demethylation of obtusifoliol to 4 alpha-methyl-5 alpha-ergosta-8,14,24(28)-trien-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] Steroid biosynthesis; zymosterol biosynthesis; zymosterol from lanosterol: step 1/6. Belongs to the cytochrome P450 family.