Hydroxyphenylpyruvate reductase E C 111237

Coleus blumei enzyme, which requires NADH reduces p -hydroxyphenylpyruvate and 3,4-dihydroxyphenylpyruvate to the corresponding lactates [E660].

Aromatic a-ketoacid reductase ((R)-aromatic lactate dehydrogenase; 1.1.1.222, diiodophenylpyruvate reductase; E.C. 1.1.1.96)

1. Reduction

Dog heart enzyme is a cytosolic dimer, monomeric molecular weight 40000, pI 5.4, which requires NADH. Activity is also found in brain, kidney and liver, and is considered to be associated with an isozyme of malate dehydrogenase. The best substrate is 3,5-diiodophenylpyruvate, with good activity towards phenylpyruvate and indole-3-pyruvate [A2917].

In vivo studies have demonstrated this activity in rat [A2961, A3327]; reduction is catalyzed by lactate dehydrogenase (E.C. 1.1.2.3) and aromatic alpha-keto acid reductase [A3327]. Highest activity is found in heart, and (in reducing order) in kidney, muscle and liver. 3,4-Dihydroxyphe-nylpyruvate is 10 times as active as 3-methoxy-4-hydroxyphenylpyruvate. Oxamate (a lactate dehydrogenase inhibitor) does not inhibit liver mitochondrial enzyme [A2983].

In a range of animals cytoplasmic malate dehydrogenase (E.C. 1.1.1.37) has been found to be identical with aromatic alpha-keto acid reductase (with p -hydroxyphenylpyruvate as substrate), with lactate dehydrogenase accounting for a minimal proportion of the total activity found in these species. The studies were carried out on flight muscle of Falco, Milvago, Herpetotheres, Phalcobanes, Spiziapteryx and Polyhierax, Palaemonedes (a marine invertebrate), and frog liver and muscle. The activity in Fundulus grandis (a marine fish) is identified as lactate dehydrogenase [E561].

Coleus blumei enzyme has an optimum pH between 6.5 and 7.0, requires NAD(P)H, and reduces the physiologically important pyruvates m- and p -hydroxy-, 3,4-dihydroxy- and 4-hydroxy-3-methoxyphenylpyruvates [E660, G289].

Candida guilliermondi enzyme requires NAD(P)H [A2483].

Candida maltosa enzyme is a tetramer, molecular weight 250 000 /280 000, monomeric molecular weight 68 000. It requires Mn2+ and NAD(P)H for reduction; the reaction is reversible, with optimum pH 6.5 for reduction, and 9.5 for oxidation. Substrates studied are phenylpyruvate, p -hydroxyphenylpyruvate, indole-3-pyruvate and the corresponding lactates [D975].

Lactobacillus casei d-hydroxyisocaproate dehydrogenase reduces phenylpyruvate to d-phenyllactate [E587].

2. Oxidation (indolelactate dehydrogenase; E.C. 1.1.1.110)

Formation of phenylpyruvate from phenyllactate has been recorded in rat, Candida, Lactobacillus, Neisseria, Pseudomonas and Rhodotorula

[B438, D975, E377, F92, G774, K95]. A similar reaction has been detected in rat for m-hydroxyphenyllactate and vanillactate [A2961]. In addition, p -hydroxyphenyllactate is oxidized by Neisseria gonorrhoeae [F92], and indole-3-lactate by Candida maltosa (see above) [D975].

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