# FAD --- **FAD**, or "flavin adenine dinucleotide" is a [[vitamin B]] coenzyme involved in several [[metabolism|metabolic reactions]]. It can exist in four redox states, FADH, FADH$_2$, or flavin-N(5)-oxide. It is a derivitave of [[vitamin B|riboflavin]]. **FADH** is the "empty" state of the electron carrier version of FAD. **FADH$_2$** is the reduced form of FADH helps out in the [[ETC (mitochondria)|ETC]] by taking the electrons from the [[citric acid cycle]]. ___