NAD-Dependent Malate Dehydrogenases

This review will deal with the NAD+-dependent malate dehydrogenases of animal tissue for which the most structural, mechanistic, and regulatory data are available. Particular attention will be directed toward the similarities and differences characterizing the cytoplasmic and mitochondrial enzymes. 

Malate dehydrogenase has been identified in a wide variety of sources and purified to homogeneity from a number of them. The majority of studies have been carried out with enzyme isolated from either pig or beef heart. The first apparently pure preparation was obtained by Wolfe and Neilands (7). It differs from previously reported procedures (S,9) 

Purification of the malate dehydrogenase isozymes from beef heart have utilized similar procedures (17-22) to those already described for 

Homogeneous preparations of malate dehydrogenase have also been isolated from chicken heart (27), horse heart (28), Drosophila virilis 

Malate dehydrogenase has also been isolated from several prokaryotes. Yoshida (33) purified the enzyme from Bacillus subtilis utilizing ammo- 

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The section which follows attempts to describe some of the more recent observations which have been made on the NAD+-dependent malate dehydrogenases. Considerably more data on the mitochondrial form are available, but for reasons of simplicity, both forms are discussed in the same section. 

The specificity of the NAD-dependent malate dehydrogenase (decarboxylase) as used In this radiometric assay was evaluated using... 

Enzymes with an initially low activity which gradually increased during embryonic development. To this group of enzymes belong fructose-1,6-diphosphate aldolase (FDP-aldolase) and NAD-dependent malate dehydrogenase (NAD-MDH). The activities of these enzymes increased gradually until the morula-blastocyst transition, whereupon the enzyme activity increased more rapidly (Epstein et al., 1969). 

FIG. 5.4 Alanine synthesis and the reoxidation of glycolytic NADH. 1, Glycolysis 2, alanine aminotransferase 3, NAD-dependent glutamate dehydrogenase 4, NADP-dependent glutamate dehydrogenase 5, malate dehydrogenase 6, malic enzyme (cytosolic). 

Physiological substrates, however, such as apotryptophan synthase, cytoplasmic malate dehydrogenase or NAD-dependent glutamate dehydrogenase from yeast, are attacked by proteinase A at neutral pH (4,7). Results from experiments on the sensitivity of hemoglobin and yeast-apotryptophan synthase, respectively, to yeast proteinase A are shown in Figure 2. 

NAD (P) " -dependent enzymes are stereospecific. Malate dehydrogenase, for example, transfers a hydride to die pro-/ position of NADH, whereas glyceraldehyde-3-phosphate dehydrogenase transfers a hydride to die pro-5 position of the nicotinamide. Alcohol dehydrogenase removes a hydride from the pro-i position of edianol and transfers it to die pro-i position of NADH. 

In this pathway the electrons for the drug reduction are generated by the oxidative decarboxylation of malate catalyzed by the NAD-dependent malic enzyme (malate dehydrogenase (decarboxylating)). The NADH produced by this reaction is reoxidized by an enzyme with NADH ferredoxin oxidoreductase activity that has been recently identified as a homologue of the NADH dehydrogenase (NDH) module of the mitochondrial respiratory complex I (Hrdy et al. 2004 and see Hrdy et al., this volume). The... 

Gajovic et al. [64] L-malate Fruits, fruit juices, ciders and wines NAD(P)+-dependent L-malate dehydrogenase oxaloacetate decarboxylating with salicylate hydroxylase (SHL)/ in gelatine membrane sandwiched between a dialysis membrane and a PET membrane Clark-electrode ... 

Esti et al. [8] L-Lactate L-Malate Micro-malolactic fermentation in red wine Lactate oxidase/in a nylon membrane with glutaraldehyde or NAD(P)+-dependent l-malate dehydrogenase oxaloacetate decarboxylating/ immobilised in an aminopropyl glass beads reactor Platinum electrode/ +650mV vs. Ag/AgCl Phenazine methosulfate (for malate sensor)... 

To understand how the TCA cycle responds kinetically to changes in demand, we can examine the predictions in time-dependent reaction fluxes in response to changes in the primary controlling variable NAD. Figure 6.4 plots predicted reaction fluxes for pyruvate dehydrogenase, aconitase, fumarase, and malate dehydrogenase in response to an instantaneous change in NAD. The initial steady state is obtained... 

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