Structural domains comprising this superfamily share the structure of the small subunit of propanediol/glycerol dehydratases. Diol dehydratase and glycerol dehydratase are two iso-functional enzymes that respectively catalyse the conversion of 1,2-propanediol, 1,2-ethanediol and glycerol to the corresponding deoxy aldehydes. This reaction proceeds by a radical mechanism involving coenzyme B12 as an essential cofactor. Even though they catalyse the same reaction, these enzymes differ in their substrate preferences, the pathways in which they participate (dihydroxyacetone [DHA] pathway for glycerol dehydratase and 1,2-propanediol degradation pathway for diol dehydratase), and in those organisms where both enzymes are produced, the genes for them are independently regulated PMID:210157,PMID:12230560.