In biological systems, FAD acts as an acceptor of H⁺ and e⁻ in its fully oxidized form, an acceptor or donor in the FADH form, and a donor in the reduced FADH₂ form.
The diagram below summarizes the potential changes that it can undergo.

Along with what is seen above, other reactive forms of FAD can be formed and consumed.
These reactions involve the transfer of electrons and the making/breaking of chemical bonds.
Through reaction mechanisms, FAD is able to contribute to chemical activities within biological systems.
The following pictures depict general forms of some of the actions that FAD can be involved in.

Mechanisms 1 and 2 represent hydride gain, in which the molecule gains what amounts to be one hydride ion.
Mechanisms 3 and 4 radical formation and hydride loss.
Radical species contain unpaired electron atoms and are very chemically active.
Hydride loss is the inverse process of the hydride gain seen before.
The final two mechanisms show nucleophilic addition and a reaction using a carbon radical.
In biological systems, FAD acts as an acceptor of H⁺ and e⁻ in its fully oxidized form, an acceptor or donor in the FADH form, and a donor in the reduced FADH₂ form. The diagram below summarizes the potential changes that it can undergo.
Along with what is seen above, other reactive forms of FAD can be formed and consumed. These reactions involve the transfer of electrons and the making/breaking of chemical bonds. Through reaction mechanisms, FAD is able to contribute to chemical activities within biological systems. The following pictures depict general forms of some of the actions that FAD can be involved in.
Mechanisms 1 and 2 represent hydride gain, in which the molecule gains what amounts to be one hydride ion. Mechanisms 3 and 4 radical formation and hydride loss. Radical species contain unpaired electron atoms and are very chemically active. Hydride loss is the inverse process of the hydride gain seen before. The final two mechanisms show nucleophilic addition and a reaction using a carbon radical.
Flavin adenine dinucleotide