Fad

FAD is an acronym used for several terms in science and related fields. In biochemistry, the most common meanings are flavin adenine dinucleotide and fatty acid desaturase. The uppercase form FAD is typical in scientific literature, while other uses may appear in broader contexts.

Flavin adenine dinucleotide (FAD) is a redox-active coenzyme derived from riboflavin (vitamin B2). It participates in oxidation–reduction reactions by cycling between oxidized FAD and reduced FADH2. FAD functions as a prosthetic group in many flavoproteins and participates in key metabolic pathways, including the citric acid cycle, beta-oxidation, and various respiratory chain reactions. Its ability to accept and donate electrons makes it essential for energy production and several biosynthetic processes. FAD can exist covalently bound to enzymes or loosely associated as a cofactor.

Fatty acid desaturase (FAD) refers to a family of membrane-bound enzymes that introduce cis double bonds into fatty acyl chains, producing unsaturated fatty acids. These enzymes are found in plants, animals, and microbes, and they localize primarily to the endoplasmic reticulum or mitochondria in many organisms. The desaturation process requires molecular oxygen and an electron transfer system, commonly provided by partners such as cytochrome b5 and its reductase in animals. By generating unsaturated fatty acids, desaturases influence membrane fluidity, signaling pathways, and lipid metabolism.

Beyond biochemistry, FAD can appear as an acronym in organizational or technical contexts, while the lowercase term fad describes a short-lived fashion or cultural phenomenon that rises quickly in popularity and then declines.