lanosterol

Lanosterol is a tetracyclic triterpenoid sterol with the chemical formula C30H50O. It is a key intermediate in the biosynthesis of sterols in animals and fungi and serves as the direct precursor to cholesterol in animals and to ergosterol in fungi. Lanosterol is produced from squalene via squalene epoxide and the action of oxidosqualene cyclase, which closes the rings to form the characteristic multi-ring steroid skeleton bearing a hydroxyl group at the C3 position.

In higher animals and many fungi, lanosterol undergoes a series of demethylation, reduction, and rearrangement reactions that convert it into the end products cholesterol or ergosterol, respectively. A major pathway in animals involves C14-demethylation and subsequent reductions that culminate in cholesterol. In fungi, similar modifications lead to ergosterol, the principal membrane sterol in most fungal species. Plants, by contrast, typically synthesize cycloartenol as the first sterol, and lanosterol is not a major constituent of plant sterol metabolism, though trace production can occur under certain conditions.

Biological role and significance: as an early intermediate in the mevalonate pathway, lanosterol connects the initial isoprenoid units to the end-point sterols essential for membrane structure and function. It is also used in biochemical research as a substrate or standard for studies of cholesterol biosynthesis and sterol metabolism.

Occurrence: lanosterol is found in animal tissues and in fungi where it is part of the sterol biosynthetic machinery. It is present in trace amounts in some foods and biological samples, reflecting its role as a biosynthetic intermediate rather than a common terminal product.