A number of oxidoreductases that act on alpha-hydroxy acids and which are FMN-containing flavoproteins have been shown [<cite idref="PUB00002617"/>, <cite idref="PUB00000334"/>, <cite idref="PUB00002664"/>] to be structurally related.The first step in the reaction mechanism of these enzymes is the abstraction of the proton from the alpha-carbon of the substrate producing a carbanion which can subsequently attach to the N5 atom of FMN. A conserved histidine has been shown [<cite idref="PUB00002533"/>] to be involved in the removal of the proton. The region around this active site residue is highly conserved and contains an arginine residue which is involved in substrate binding.