Mandelate racemase (MR) catalyzes the Mg2+-dependent 1,1-proton transfer reaction that interconverts the enantiomers of mandelic acid. MR is the first enzyme in the bacterial pathway that converts mandelic acid to benzoic acid and allows this pathway to utilize either enantiomer of mandelate. MR belongs to the enolase superfamily of enzymes, characterized by the presence of an enolate anion intermediate which is generated by abstraction of the alpha-proton of the carboxylate substrate by an active site residue and is stabilized by coordination to the essential Mg2+ ion.
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