Accepted name: (R)-mandelate dehydrogenase
Reaction: (R)-mandelate + NAD+ = phenylglyoxylate + NADH + H+
Glossary: (R)-mandelate = D-mandelate
Other name(s): ManDH2; D-ManDH2; D-mandelate dehydrogenase (ambiguous)
Systematic name: (R)-mandelate:NAD+ 2-oxidoreductase
Comments: The enzyme, found in bacteria and fungi, can also accept a number of substituted mandelate derivatives, such as 3-hydroxymandelate, 4-hydroxymandelate, 2-methoxymandelate, 4-hydroxy-3-methoxymandelate and 3-hydroxy-4-methoxymandelate. The enzyme has no activity with (S)-mandelate (cf. EC, (S)-mandelate dehydrogenase) [1,2]. The enzyme transfers the pro-R-hydrogen from NADH [2].
1.  Baker, D.P. and Fewson, C.A. Purification and characterization of D(–)-mandelate dehydrogenase from Rhodotorula graminis. Microbiology 135 (1989) 2035–2044.
2.  Baker, D.P., Kleanthous, C., Keen, J.N., Weinhold, E. and Fewson, C.A. Mechanistic and active-site studies on D(–)-mandelate dehydrogenase from Rhodotorula graminis. Biochem. J. 281 (1992) 211–218. [PMID: 1731758]
[EC created 2014]
Accepted name: (S)-mandelate dehydrogenase
Reaction: (S)-mandelate + acceptor = phenylglyoxylate + reduced acceptor
Glossary: (S)-mandelate = (S)-2-hydroxy-2-phenylacetate
phenylglyoxylate = benzoylformate = 2-oxo-2-phenylacetate
Other name(s): MDH (ambiguous)
Systematic name: (S)-mandelate:acceptor 2-oxidoreductase
Comments: This enzyme is a member of the FMN-dependent α-hydroxy-acid oxidase/dehydrogenase family [1]. While all enzymes of this family oxidize the (S)-enantiomer of an α-hydroxy acid to an α-oxo acid, the ultimate oxidant (oxygen, intramolecular heme or some other acceptor) depends on the particular enzyme. This enzyme transfers the electron pair from FMNH2 to a component of the electron transport chain, most probably ubiquinone [1,2]. It is part of a metabolic pathway in Pseudomonads that allows these organisms to utilize mandelic acid, derivatized from the common soil metabolite amygdalin, as the sole source of carbon and energy [2]. The enzyme has a large active-site pocket and preferentially binds substrates with longer sidechains, e.g. 2-hydroxyoctanoate rather than 2-hydroxybutyrate [1]. It also prefers substrates that, like (S)-mandelate, have β unsaturation, e.g. (indol-3-yl)glycolate compared with (indol-3-yl)lactate [1]. Esters of mandelate, such as methyl (S)-mandelate, are also substrates [3].
1.  Lehoux, I.E. and Mitra, B. (S)-Mandelate dehydrogenase from Pseudomonas putida: mechanistic studies with alternate substrates and pH and kinetic isotope effects. Biochemistry 38 (1999) 5836–5848. [PMID: 10231535]
2.  Dewanti, A.R., Xu, Y. and Mitra, B. Role of glycine 81 in (S)-mandelate dehydrogenase from Pseudomonas putida in substrate specificity and oxidase activity. Biochemistry 43 (2004) 10692–10700. [PMID: 15311930]
3.  Dewanti, A.R., Xu, Y. and Mitra, B. Esters of mandelic acid as substrates for (S)-mandelate dehydrogenase from Pseudomonas putida: implications for the reaction mechanism. Biochemistry 43 (2004) 1883–1890. [PMID: 14967029]
[EC created 2006]
Accepted name: mandelate racemase
Reaction: (S)-mandelate = (R)-mandelate
Glossary: mandelate = 2-hydroxy-2-phenylacetate
Systematic name: mandelate racemase
1.  Gunsalus, C.F., Stanier, R.Y. and Gunsalus, I.C. The enzymatic conversion of mandelic acid to benzoic acid. III. Fractionation and properties of the soluble enzymes. J. Bacteriol. 66 (1953) 548–553. [PMID: 13108854]
[EC created 1961]