Views: 3 Author: Site Editor Publish Time: 2023-04-14 Origin: Site
Squalene is an organic compound.It is a triterpenoid with the molecular formula C30H50.It is a colorless oil, but impure samples are yellow.It was originally extracted from shark liver oil (hence the name, since dogfish is a genus of sharks).An estimated 12 percent of the squalene in the human body is found in sebum.Squalene has topical skin lubricating and protective effects.Most plants,fungi and animals produce squalene as a biochemical precursor for the biosynthesis of sterols, including cholesterol and steroid hormones in humans.It is also an intermediate in terpenoid biosynthesis in many bacteria.Squalene is an important component of some vaccine adjuvants:Novartis and GlaxoSmithKline’s adjuvants are called MF59 and AS03 respectively.
Role in triterpenoid synthesis
Squalene is a biochemical precursor of steroids and hopanes.For sterols, squalene conversion begins with the oxidation of one of its terminal double bonds (by squalene monooxygenase), resulting in 2,3-oxysqualene.This is followed by enzymatic cyclization to produce lanosterol, which can be processed into other steroids,such as cholesterol and ergosterol double bonds, through multiple steps including removal of three methyl groups, reduction of one double bond by NADPH, and migration of the other double bond In many plants it is converted to stigmasterol, and in many fungi it is a precursor to ergosterol.Biosynthetic pathways are present in many bacteria  and most eukaryotes, but have not been found in archaea.
Squalene is biosynthesized by coupling two molecules of farnesyl pyrophosphate.The condensation requires NADPH and squalene synthase.
Squalene monooxygenase (also known as squalene epoxidase) is a eukaryotic enzyme that uses NADPH and diatomic oxygen to oxidize squalene to 2,3-oxysqualene (squalene epoxy).Squalene epoxidase catalyzes the first oxidative step in sterol biosynthesis and is considered to be one of the rate-limiting enzymes in this pathway.In humans, squalene epoxidase is encoded by the SQLE gene.Some eukaryotic genomes lack the gene encoding squalene monooxygenase and instead encode an alternative squalene epoxidase to perform the same task.
Typical squalene monooxygenase is a flavoprotein monooxygenase.Flavoprotein monooxygenases form flavin hydroperoxides at the enzyme active site and then transfer the terminal oxygen atoms of the hydroperoxides to the substrate.Squalene monooxygenase differs from other flavin monooxygenases in that the oxygen inserts into the substrate as an epoxide rather than a hydroxyl group. This enzyme contains loosely bound FAD flavin and receives electrons from NADPH-cytochrome P450 reductase instead of directly binding NADPH.Alternative squalene epoxidase belongs to the superfamily of fatty acid hydroxylases and receives electrons from cytochrome b5.