These proteins are involved in a wide array of biological processes, including removal of radicals contributing to oxidative stress, photosynthesis, and DNA repair.

The flavin is generally tightly bound (as in adrenodoxin reductase, wherein the FAD is buried deeply).

Its structure was determined and reported in 1935 and given the name riboflavin, derived from the ribityl side chain and yellow colour of the conjugated ring system.

Hugo Theorell and coworkers showed that a bright-yellow-coloured yeast protein, identified previously as essential for cellular respiration, could be separated into apoprotein and a bright-yellow pigment.

This led to the discovery that the protein studied required not riboflavin but flavin mononucleotide to be catalytically active.