Non-heme iron oxygenase involved in sterols biosynthesis by catalyzing the removal of the second methyl group at the C-4 position (PubMed:11707264). 24-ethylidenelophenol and 24-ethyllophenol are the preferred substrates (PubMed:11707264). Together with SMO2-2, required during embryogenesis, probably by maintaining sterols and auxin homeostasis (PubMed:27006488). 4,4-dimethyl-5alpha-cholest-7-en-3beta-ol + 6 Fe(II)-[cytochrome b5] + 5 H(+) + 3 O2 = 4alpha-carboxy-4beta-methyl-5alpha-cholest-7-ene-3beta-ol + 6 Fe(III)-[cytochrome b5] + 4 H2O 24-methylidenelophenol + 6 Fe(II)-[cytochrome b5] + 5 H(+) + 3 O2 = 4alpha-carboxy-ergosta-7,24(24(1))-dien-3beta-ol + 6 Fe(III)-[cytochrome b5] + 4 H2O Strongly expressed in leaves, flowers, siliques and developing seeds. In leaves, mostly expressed in vascular tissues and trichomes (PubMed:27006488). In flowers, accumulates mainly in sepals, stamen filaments, pollen grains and pistils, but barely detectable in petals (PubMed:27006488). Present in siliques at all stages of development (PubMed:27006488). During embroygenesis, expressed in both embryos and endosperms throughout embryonic development (PubMed:27006488). The histidine box domains may contain the active site and/or be involved in metal ion binding. No obvious phenotype (PubMed:27006488). The smo2-1 smo2-2 double mutant accumulates the 4alpha-methylsterols 24-ethylidene lophenol and 24-ethyl lophenol, and is embryonic lethal, arrested in early stages with an altered endosperm development, probably due to disturbed auxin flux and responses (PubMed:27006488). Requires a membrane-bound cytochrome b5 as an obligatory electron carrier from NAD(P)H to SMO. Belongs to the sterol desaturase family.