A functionally diverse enzyme superfamily that abstracts the alpha protons of carboxylic acids.

Mandelate racemase and muconate lactonizing enzyme are structurally homologous but catalyze different reactions, each initiated by proton abstraction from carbon. The structural similarity to mandelate racemase of a previously unidentified gene product was used to deduce its function as a galactonate dehydratase. In this enzyme superfamily that has evolved to catalyze proton abstraction from carbon, three variations of homologous active site architectures are now represented: lysine and histidine bases in the active site of mandelate racemase, only a lysine base in the active site of muconate lactonizing enzyme, and only a histidine base in the active site of galactonate dehydratase. This discovery supports the hypothesis that new enzymatic activities evolve by recruitment of a protein catalyzing the same type of chemical reaction.