EC 1.1.1.379     
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 1.1.99.31, (S)-mandelate dehydrogenase) [1,2]. The enzyme transfers the pro-R-hydrogen from NADH [2].
References:
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 1.1.1.379 created 2014]
 
 
EC 1.1.3.46     
Accepted name: 4-hydroxymandelate oxidase
Reaction: (S)-4-hydroxymandelate + O2 = 2-(4-hydroxyphenyl)-2-oxoacetate + H2O2
Glossary: (S)-4-hydroxymandelate = (S)-2-hydroxy-2-(4-hydroxyphenyl)acetate
2-(4-hydroxyphenyl)-2-oxoacetate = 4-hydroxyphenylglyoxylate = (4-hydroxyphenyl)(oxo)acetate
L-(4-hydroxyphenyl)glycine = (S)-4-hydroxyphenylglycine
L-(3,5-dihydroxyphenyl)glycine = (S)-3,5-dihydroxyphenylglycine
Other name(s): 4HmO; HmO
Systematic name: (S)-4-hydroxymandelate:oxygen 1-oxidoreductase
Comments: A flavoprotein (FMN). The enzyme from the bacterium Amycolatopsis orientalis is involved in the biosynthesis of L-(4-hydroxyphenyl)glycine and L-(3,5-dihydroxyphenyl)glycine, two non-proteinogenic amino acids occurring in the vancomycin group of antibiotics.
References:
1.  Hubbard, B.K., Thomas, M.G. and Walsh, C.T. Biosynthesis of L-p-hydroxyphenylglycine, a non-proteinogenic amino acid constituent of peptide antibiotics. Chem. Biol. 7 (2000) 931–942. [PMID: 11137816]
2.  Li, T.L., Choroba, O.W., Charles, E.H., Sandercock, A.M., Williams, D.H. and Spencer, J.B. Characterisation of a hydroxymandelate oxidase involved in the biosynthesis of two unusual amino acids occurring in the vancomycin group of antibiotics. Chem. Commun. (Camb.) (2001) 1752–1753. [PMID: 12240298]
[EC 1.1.3.46 created 2014]
 
 
EC 1.1.99.31     
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].
References:
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 1.1.99.31 created 2006]
 
 
EC 1.2.1.58     
Accepted name: phenylglyoxylate dehydrogenase (acylating)
Reaction: phenylglyoxylate + NAD+ + CoA = benzoyl-S-CoA + CO2 + NADH
Systematic name: phenylglyoxylate:NAD+ oxidoreductase
Comments: Requires thiamine diphosphate as cofactor. The enzyme from the denitrifying bacterium Azoarcus evansii is specific for phenylglyoxylate. 2-Oxoisovalerate is oxidized at 15% of the rate for phenylglyoxylate. Also reduces viologen dyes. Contains iron-sulfur centres and FAD.
References:
1.  Hirsch, W., Schägger, H. and Fuchs, G. Phenylglyoxylate:NAD+ oxidoreductase (CoA benzoylating), a new enzyme of anaerobic phenylalanine metabolism in the denitrifying bacterium Axoarcus evansii. Eur. J. Biochem. 251 (1998) 907–915. [PMID: 9490067]
[EC 1.2.1.58 created 1999]
 
 
EC 1.17.5.1     
Accepted name: phenylacetyl-CoA dehydrogenase
Reaction: phenylacetyl-CoA + H2O + 2 quinone = phenylglyoxylyl-CoA + 2 quinol
Other name(s): phenylacetyl-CoA:acceptor oxidoreductase
Systematic name: phenylacetyl-CoA:quinone oxidoreductase
Comments: The enzyme from Thauera aromatica is a membrane-bound molybdenum—iron—sulfur protein. The enzyme is specific for phenylacetyl-CoA as substrate. Phenylacetate, acetyl-CoA, benzoyl-CoA, propanoyl-CoA, crotonyl-CoA, succinyl-CoA and 3-hydroxybenzoyl-CoA cannot act as substrates. The oxygen atom introduced into the product, phenylglyoxylyl-CoA, is derived from water and not molecular oxygen. Duroquinone, menaquinone and 2,6-dichlorophenolindophenol (DCPIP) can act as acceptor, but the likely physiological acceptor is ubiquinone [1]. A second enzyme, EC 3.1.2.25, phenylacetyl-CoA hydrolase, converts the phenylglyoxylyl-CoA formed into phenylglyoxylate.
References:
1.  Rhee, S.K. and Fuchs, G. Phenylacetyl-CoA:acceptor oxidoreductase, a membrane-bound molybdenum-iron-sulfur enzyme involved in anaerobic metabolism of phenylalanine in the denitrifying bacterium Thauera aromatica. Eur. J. Biochem. 262 (1999) 507–515. [PMID: 10336636]
2.  Schneider, S. and Fuchs, G. Phenylacetyl-CoA:acceptor oxidoreductase, a new α-oxidizing enzyme that produces phenylglyoxylate. Assay, membrane localization, and differential production in Thauera aromatica. Arch. Microbiol. 169 (1998) 509–516. [PMID: 9575237]
[EC 1.17.5.1 created 2004]
 
 
EC 2.6.1.72     
Accepted name: D-4-hydroxyphenylglycine transaminase
Reaction: D-4-hydroxyphenylglycine + 2-oxoglutarate = 4-hydroxyphenylglyoxylate + L-glutamate
Other name(s): D-hydroxyphenylglycine aminotransferase
Systematic name: D-4-hydroxyphenylglycine:2-oxoglutarate aminotransferase
Comments: A pyridoxal-phosphate protein.
References:
1.  Van den Tweel, W.J.J., Ogg, R.L.H.P. and de Bont, J.A.M. Transamination with a D-transaminase from Pseudomonas putida and conversion of p-hydroxyphenylglyoxylate to D-p-hydroxyphenylglycine. Patent EP0315786, Neth. Appl. NL (1987), 87, 02449.
2.  Van den Tweel, W.J.J., Smits, J.P., Ogg, R.L.H.P. and de Bont, J.A.M. The involvement of an enantioselective transaminase in the metabolism of D-3- and D-4-hydroxyphenylglycine in Pseudomonas putida. Appl. Microbiol. Biotechnol. 29 (1998) 224–230.
[EC 2.6.1.72 created 1990]
 
 
EC 3.1.2.25     
Accepted name: phenylacetyl-CoA hydrolase
Reaction: phenylglyoxylyl-CoA + H2O = phenylglyoxylate + CoA
Systematic name: phenylglyoxylyl-CoA hydrolase
Comments: This is the second step in the conversion of phenylacetyl-CoA to phenylglyoxylate, the first step being carried out by EC 1.17.5.1, phenylacetyl-CoA dehydrogenase.
References:
1.  Rhee, S.K. and Fuchs, G. Phenylacetyl-CoA:acceptor oxidoreductase, a membrane-bound molybdenum-iron-sulfur enzyme involved in anaerobic metabolism of phenylalanine in the denitrifying bacterium Thauera aromatica. Eur. J. Biochem. 262 (1999) 507–515. [PMID: 10336636]
2.  Schneider, S. and Fuchs, G. Phenylacetyl-CoA:acceptor oxidoreductase, a new α-oxidizing enzyme that produces phenylglyoxylate. Assay, membrane localization, and differential production in Thauera aromatica. Arch. Microbiol. 169 (1998) 509–516. [PMID: 9575237]
[EC 3.1.2.25 created 2004]
 
 
EC 4.1.1.7     
Accepted name: benzoylformate decarboxylase
Reaction: phenylglyoxylate = benzaldehyde + CO2
Glossary: thiamine diphosphate = 3-[(4-amino-2-methylpyrimidin-5-yl)methyl]-5-(2-diphosphoethyl)-4-methyl-1,3-thiazolium
phenylglyoxylate = benzoylformate = 2-oxo-2-phenylacetate
Other name(s): phenylglyoxylate decarboxylase; benzoylformate carboxy-lyase; benzoylformate carboxy-lyase (benzaldehyde-forming)
Systematic name: phenylglyoxylate carboxy-lyase (benzaldehyde-forming)
Comments: A thiamine-diphosphate protein.
References:
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 4.1.1.7 created 1961]