<p>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. These enzymes are:</p><p> <ul> <li>Lactate dehydrogenase (<db_xref db="EC" dbkey="1.1.2.3"/>), which consists of a dehydrogenase domain and a haem-binding domain called cytochrome b2 and which catalyses the conversion of lactate into pyruvate.</li><li>Glycolate oxidase (<db_xref db="EC" dbkey="1.1.3.15"/>) ((S)-2-hydroxy-acid oxidase), a peroxisomal enzyme that catalyses the conversion of glycolate and oxygen to glyoxylate and hydrogen peroxide.</li><li>Long chain alpha-hydroxy acid oxidase from rat (<db_xref db="EC" dbkey="1.1.3.15"/>), a peroxisomal enzyme.</li><li>Lactate 2-monooxygenase (<db_xref db="EC" dbkey="1.13.12.4"/>) (lactate oxidase) from <taxon tax_id="1772">Mycobacterium smegmatis</taxon>, which catalyses the conversion of lactate and oxygen to acetate, carbon dioxide and water.</li><li>(S)-mandelate dehydrogenase from <taxon tax_id="303">Pseudomonas putida</taxon> (gene mdlB), which catalyses the reduction of (S)-mandelate to benzoylformate.</li> </ul> </p><p>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.</p>