Pyruvic acid dehydrogenase

Enzyme catalyzed reductions of carbonyl groups are more often than not com pletely stereoselective Pyruvic acid for example is converted exclusively to (5) (+) lactic acid by the lactate dehydrogenase NADH system (Section 15 11) The enantiomer... 

Carboxylic acids with labile a-methylene protons react with isatin in the presence of strong aqueous base. In the total synthesis of methoxatin, the coenzyme of methanol dehydrogenase and glucose dehydrogenase, Weinreb employs a Pfitzinger condensation of an isatin 37 and pyruvic acid as a key step to provide the 4-quinolinic acid 38 in 50% yield under the standard basic conditions. ... 

Revised spectrophotometric methods for the determination of glutamic-oxaloacetic transaminase, glutamic-pyruvic transaminase and lactic acid dehydrogenase. Am. J. Clin. Path. (1960), 34, 381-398. 

Similarly, the pyruvate dehydrogenase complex (PDC) can be activated directly by electrogenerated methyl viologen radical cations (MV +) as mediator. Thus, the naturally PDC-catalyzed oxidative decarboxylation of pyruvic acid in the... 

Thiamine pyrophosphate is a coenzyme for several enzymes involved in carbohydrate metabolism. These enzymes either catalyze the decarboxylation of oi-keto acids or the rearrangement of the carbon skeletons of certain sugars. A particularly important example is provided by the conversion of pyruvic acid, an oi-keto acid, to acetic acid. The pyruvate dehydrogenase complex catalyzes this reaction. This is the key reaction that links the degradation of sugars to the citric acid cycle and fatty acid synthesis (chapters 16 and 18) ... 

In contrast, amino acid dehydrogenases comprise a well-known class of enzymes with industrial apphcations. An illustrative example is the Evonik (formerly Degussa) process for the synthesis of (S)-tert-leucine by reductive amination of trimethyl pyruvic acid (Scheme 6.12) [27]. The NADH cofactor is regenerated by coupling the reductive amination with FDH-catalyzed reduction of formate, which is added as the ammonium salt. 

EC 1.1.1.14 L-Iditol dehydrogenase EC 1.1.1.27 Lactate dehydrogenase L-Iditol + NAD + t L-sorbose + NADH Lactic acid + NAD+ pyruvic acid + NADH + H + — SM... 

Reed, L.J. Damuni, Z. Merryfield, M.L. Regulation of mammalian pyruvate and branched-chain a-keto acid dehydrogenase complexes by phosphorylation-dephosphorylation. Curr. Top. Cell. ReguL, 27, 41-49 (1985)... 

Experiments with rats have shown that the branched-chain a-keto acid dehydrogenase complex is regulated by covalent modification in response to the content of branched-chain amino acids in the diet. With little or no excess dietary intake of branched-chain amino acids, the enzyme complex is phosphorylated and thereby inactivated by a protein kinase. Addition of excess branched-chain amino acids to the diet results in dephosphoiylation and consequent activation of the enzyme. Recall that the pyruvate dehydrogenase complex is subject to similar regulation by phosphorylation and dephosphorylation (p. 621). 

NADH as an end product. This implicates oxidized malic acid, either pyruvic or oxaloacetic acid, as another end product. By adding commercial preparations of L-lactic dehydrogenase or malic dehydrogenase to the reaction mixture, Morenzoni (90) concluded that the end product was pyruvic acid. Attempts were then made to show whether two enzymes—malate carboxy lyase and the classic malic enzyme, malate oxidoreductase (decarboxylating), were involved or if the two activities were on the same enzyme. The preponderance of evidence indicated that only one enzyme is involved. This evidence came from temperature inactivation studies, heavy-metal inhibition studies, and ratio measurements of the two activities of partially purified preparations of Schiitz and Radlers malo-lactic enzyme (76, 90). This is not the first case of a single enzyme having two different activities (91). 

In the Korkes and Ochoa (11) mechanism proposed for the malo-lactic reaction (see top of next page), pyruvic acid is either a short-lived, fleeting intermediate, or it is bound to malic enzyme so that as soon as it is formed by the enzyme, it is converted to lactic acid by lactate dehydrogenase. [Both malic enzyme ( malic ) and malate dehydrogenase (de-... 

When considering the mechanism of the malo-lactic fermentation, the possibility that malic acid may be converted first to oxaloacetic acid (by malic dehydrogenase) must be recognized. This acid could then be decarboxylated to pyruvic acid, and subsequent reaction would yield lactic acid. However, if this were the case, there then should be no situation where malic acid would be decarboxylated faster than oxaloacetic acid. This, however, was shown to occur at pH 6 (14). Similarly, Flesch and Holbach (15) report that malic dehydrogenase has an optimal pH of 10, but that the malo-lactic reaction proceeds at pH 5.6. Therefore, it would not seem likely that the cell would degrade malic acid by this mechanism hence, the oxaloacetic acid intermediate would not be available to the organism. 

They stated further that, the new adaptive enzyme catalyzing Reaction 3 appears to be similar to the malic enzyme of pigeon liver, although strictly DPN (instead of TPN)-specific. The coenzyme specificity explains the ready occurrence of Reaction 1. Therefore, the authors showed that exogenous NAD was required for the overall reaction (malic acid -> lactic acid), but because this activity was measured manometrically, they never demonstrated the formation of reduced NAD. Similarly, they did not attempt to show that pyruvic acid was the intermediate between L-malic acid and lactic acid. Instead, the formation of pyruvic acid was inferred from the NAD requirement and because the malic acid dissimilation activity remained constant during purification while the lactate dehydrogenase activity decreased (14). In fact, attempts to show any appreciable amounts of pyruvic acid intermediate failed (22). 

It is not surprising that the pyruvic acid intermediate seemed plausible because in a paper earlier in that same year (23), the authors described a malic enzyme from pigeon liver. This enzyme was shown to form appreciable amounts of pyruvic acid from malic acid, but it was NADP instead of NAD specific. The end product was shown to be pyruvic acid by spectrophotometric assay involving lactate dehydrogenase. 

Some examples follow that illustrate the remarkable specificity of this kind of redox system. One of the last steps in the metabolic breakdown of glucose (glycolysis Section 20-10A) is the reduction of 2-oxopropanoic (pyruvic) acid to L-2-hydroxypropanoic (lactic) acid. The reverse process is oxidation of l-lactic acid. The enzyme lactic acid dehydrogenase catalyses this reaction, and it functions only with the L-enantiomer of lactic acid ... 

These results confirmed that branched-chain amino acid catabolism via the BCDH reaction provides the fatty acid precursors for natural avermectin biosynthesis in S. avermitilis. In contrast, B. subtilis appears to possess two mechanisms for branched-chain precursor supply. The dual substrate pyruvate/branched-chain a-keto acid dehydrogenase (aceA) and an a-keto acid dehydrogenase (bfmB), which also has some ability to metabolize pyruvate, appears to be primarily involved in supplying the branched-chain initiators of long, branched-chain fatty acid biosynthesis [32,42], Two mutations are therefore required to generate the bkd phenotype in B. subtilis [31,42],... 

Reduction of achiral precursors is often used to produce chiral products. The advantage of this approach is that the theoretical yield of product is 100% compared to the 50% theoretical maximum for the resolution of racemates. Cross-linked crystals of lactate dehydrogenase have been used to prepare L-lactic acid from pyruvic acid in an electrolytic cell. The LDH CLCs maintained constant... 

With the help of this method, His-tagged L-lactate dehydrogenase was immobilized. By pumping pyruvic acid as substrate with NADH as cofactor, it was demonstrated that the enzyme was still active in the microchannel. In this case, cofactor was used up. Srinivasan et al. [433] incorporated PikC hydroxylase from Streptomyces venezuelae into a PDMS-based microfluidic channel with a similar approach. The enzyme was immobilized to Ni-NTA agarose beads with an in situ attachment, following the addition of the beads to the microchannel. This enabled the rapid hydroxylation of the macrolide YC-17 to methymycin and neomethymycin (Scheme 4.104) in about equal amounts with a conversion of >90% at a flow rate of 70nl/min. 

---