It is a steroid demethylation inhibitor, specifically inhibiting ergosterol biosynthesis. This enzyme participates in the sterol biosynthesis pathway that leads from lanosterol to ergosterol. Other components are common sterol derivatives (fucosterol, ergosterol and cholesterol). Allylamines inhibit squalene epoxidase, another enzyme required for ergosterol synthesis. Morpholine derivatives used as agricultural fungicides in cereals are known as ergosterol biosynthesis inhibitors. The polyene antimycotics bind with sterols in the fungal cell membrane, principally ergosterol. Tempeh contains ergosterol (provitamin D2). Tryptophan is found in the fungal membrane in addition to lipids such as ergosterol. Amphotericin B, an antifungal drug, targets ergosterol. It binds to ergosterol, a major component of the fungal cell membrane. Vitamin D is produced by ultraviolet irradiation of ergosterol found in many fungi. Oxygen is necessary for the synthesis of ergosterol in fungi. This interrupts the conversion of lanosterol to ergosterol, a component of the fungal cell membrane. Exposure to ultraviolet light causes a photochemical reaction that converts ergosterol to ergocalciferol. In fungi, lanosterol is then converted to ergosterol; in humans, lanosterol becomes cholesterol.