2-keto acid oxidoreductase

Brown DM, Upcroft JA, Dodd HN, Chen N, Upcroft P (1999) Alternative 2-keto acid oxidoreductase activities in Trichomonas vaginalis. Mol Biochem Parasitol 98 203-214 Carlier JP, Sellier N, Rager MN, Reysset G (1997) Metabolism of a 5-nitroimidazole in susceptible and resistant isogenic strain of Bacterioides fragilis. Antimicrob Agents Chemother 41 1495-1499... 

Schut GJ, Menon AL, Adams MWW (2001) 2-Keto acid oxidoreductases from Pyrococcus furiosus and Thermococcus litoralis. Methods Enzymol 331 144—158... 

The two oxidoreductase systems most frequentiy used for preparation of chiral synthons include baker s yeast and horse hver alcohol dehydrogenase (HLAD). The use of baker s yeast has been recendy reviewed in great detail (6,163) and therefore will not be coveted here. The emphasis here is on dehydrogenase-catalyzed oxidation and reduction of alcohols, ketones, and keto acid, oxidations at unsaturated carbon, and Bayer-Vidiger oxidations. 

Other non-heme enzymes that use dioxygen are 4-methoxy-benzoate O-demethylase, extradiol catechol dioxygenases, the oxidoreductase isopenicillin N synthase, and a-keto acid-dependent enzymes (28). Moreover, the BH4-dependent glyceryl-ether monooxygenase (GEM) also appears to be dependent on nonheme iron for catalysis (see also Section I.E). 

The simplest example of such reactions is the decarboxylation of pyruvate. Both model and enzyme studies have shown the intermediacy of covalent complexes formed between the cofactor and the substrate. Kluger and coworkers have studied extensively the chemical and enzymatic behavior of the pyruvate and acetaldehyde complexes of ThDP (2-lactyl or LThDP, and 2-hydroxyethylThDP or HEThDP, respectively) . As Scheme 1 indicates, the coenzyme catalyzes both nonoxidative and oxidative pathways of pyruvate decarboxylation. The latter reactions are of immense consequence in human physiology. While the oxidation is a complex process, requiring an oxidizing agent (lipoic acid in the a-keto acid dehydrogenases , or flavin adenine dinucleotide, FAD or nicotinamide adenine dinucleotide , NAD " in the a-keto acid oxidases and Fe4.S4 in the pyruvate-ferredoxin oxidoreductase ) in addition to ThDP, it is generally accepted that the enamine is the substrate for the oxidation reactions. 

Oxidoreductases CoA thioester formation through oxidative decarboxylation of a-keto acids... 

The pyruvate oxidase belongs to the oxidoreductases and requires two coenzymes. One is thiamine diphosphate 104 (Figure 40), which is found in various enzymes of carbohydrate metabolite pathways like in transketo-lases, pyruvate decarboxylases, and like in the following example the oxidative decarboxylation of an a-keto acid (pyruvate oxidase). The second coenzyme is flavin adenine... 

Mai XH, Adams MWW (1996) Characterization of a fourth type of 2-keto acid-oxidizing enzyme from a hyperthermophilic archaeon 2-ketoglutarate ferredoxin oxidoreductase from Thermococcus litoralis. J Bacteriol 178 5890-5896... 

Benzoylformate decarboxylase from Pseudomonas and Acinetobacter species, also an a-keto acid decarboxylase, has higher substrate specificity than pyruvate decarboxylase. Cells of these species grown in media inducing the mandelate pathway enzymes can convert benzoylformate and acetaldehyde to optically active 2-hydroxypropiophenone. Benzaldehyde is produced in this biotransformation reaction, as it is the normal product of benzoylformate decarboxylase. Some benzyl alcohol is also produced, in this case probably by reduction of benzaldehyde by cell oxidoreductases. In the case of P. putida the (S) enantiomer form of 2-hydrox) ropiophenone was produced, with an e.e. of 91-92%. The same product produced by A. calcoaceticus had an e.e. of 98%. An optimal volumetric production of 2-hydroxypropiophenone of 6.95 g per L per h was reported. 

The peptide sequences obtained for codeinone reductase aligned well with the amino acid sequences for 6 -deoxychalcone synthase (chalcone reductase) from alfalfa, Glycerrhiza, and soybean. Knowledge of the relative positions of the peptides allowed for a quick RT-PCR based isolation of cDNAs encoding codeinone reductase from P. somniferum. The codeinone reductase isoforms are 53 % identical to chalcone reductase from soybean.25 By sequence comparison, both codeinone reductase and chalcone reductase belong to the aldo/keto reductase family, a group of structurally and functionally related NADPH-dependent oxidoreductases, and thereby possibly arise from primary metabolism. Six alleles encoding codeinone... 

Glucose-grown cells of G. candidum SC 5469 have also catalyzed die stereoselective reduction of ethyl, isopropyl, and terdary butyl esters of 4-chloro-3-oxobutanoic acid and both methyl and ethyl esters of 3-bromo-3-oxobutanoic acid. A reaction yield of more than 85% and e.e. s of more than 94% were obtained. NAD -dependent oxidoreductase responsible for the stereoselective reduction of P-keto esters of 4-chloro- and 4-bromo-3-oxobutanoic acid was purified 100-fold. The molecular weight of purified enzyme is 950,000. The purified oxidoreductase was immobilized on Eupergit C and used to catalyze the reduction of 52 to 5-(—)-53. The cofactor NAD required for the reduction reaction was regenerated by glucose dehydrogenase. 

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