desaturase

Desaturase refers to a family of enzymes that introduce cis double bonds into preexisting fatty acyl chains, converting saturated fatty acids into unsaturated ones. They are found across organisms, including animals, plants, fungi, and bacteria, and are typically membrane-bound, residing in the endoplasmic reticulum or, in some cases, plastids or mitochondria. The position of the introduced double bond is usually described using delta (Δ) notation, such as Δ9-desaturases.

Mechanistically, desaturases catalyze oxidative dehydrogenation reactions that require molecular oxygen and electron transfer from NADH through a cytochrome b5 system. The reaction removes two hydrogen atoms from the substrate to form a cis double bond. Enzymes are often specific for substrate type (fatty acyl-CoA, acyl-lipid) and for the carbon position of the new double bond.

Notable examples include in animals the stearoyl-CoA desaturase-1 (SCD1), a Δ9-desaturase that converts stearoyl-CoA to oleoyl-CoA and influences membrane fluidity and lipid signaling. In plants, a broader set of desaturases operates, including Δ12-desaturases (e.g., FAD2) that convert oleic acid to linoleic acid and Δ15-desaturases (e.g., FAD3) that produce α-linolenic acid; some desaturation steps occur in plastids, others in the endoplasmic reticulum.

Functionally, desaturases regulate the balance between saturated and unsaturated fatty acids in membrane lipids and storage lipids, thereby affecting membrane properties and the supply of polyunsaturated fatty acids for signaling. Regulation of desaturase activity is responsive to diet, hormones, and metabolic state, and dysregulation has been linked to metabolic disorders and inflammatory processes in various contexts. Genetic studies commonly examine SCD and FADS family desaturases.