Malate dehydrogenase decarboxylating

Malic enzyme (malate dehydrogenase (decarboxylating), EC 1.1.1.39) catalyzes reversible oxidative decarboxylation of malate to pyruvate. The enzyme uses NAD+ as an electron acceptor, but it is also able to utilize NADP+ with lower affinity (Drmota et al. 1996). With a subunit size of approximately 63 kDa, the Trichomonas hydrogenosomal malic enzyme belongs to the family of large, eukaryotic type of malic enzymes. In contrast, the approximately 40-kDa-subunit malic enzyme, located in the cytosol, belongs... 

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... 

Mitochondrial malate dehydrogenase, decarboxylating (malic enzyme) and transhydrogenase activities of adult Hymenolepis microstoma (Cestoda). Journal of Parasitology, 68 213-20. 

EC 1.1.1.39 Malate dehydrogenase (decarboxylating) pyruvate+nadred+co2tot=malate+nadox+h2o... 

Malic Enzyme (officially named malate dehydrogenase-decarboxylating NADP+) catalyzes the reaction below. 

This enzyme also oxidises some other 2-hydroxydicarboxylic acids. It is one of the enzymes of the citric acid cycle in which it catalyses the conversion of malate to oxalacetate. It should not be confused with malate dehydrogenase (decarboxylating) E.C. 1.1.1.40. It may be assayed by u.v. spectroscopy, if the system is driven in reverse... 

Mukerji,S.K., Ting, I. P. Malate dehydrogenase (decarboxylating) (NADP) isoenzymes of Opuntia stem tissue. Mitochondria, chloroplast, and soluble forms. Biochem. Biophys. Acta ]67,239-249 (1968 a)... 

Compartmentation of these reactions to prevent photorespiration involves the interaction of two cell types, mescrphyll cells and bundle sheath cells. The meso-phyll cells take up COg at the leaf surface, where Og is abundant, and use it to carboxylate phosphoenolpyruvate to yield OAA in a reaction catalyzed by PEP carboxylase (Figure 22.30). This four-carbon dicarboxylic acid is then either reduced to malate by an NADPH-specific malate dehydrogenase or transaminated to give aspartate in the mesophyll cells. The 4-C COg carrier (malate or aspartate) then is transported to the bundle sheath cells, where it is decarboxylated to yield COg and a 3-C product. The COg is then fixed into organic carbon by the Calvin cycle localized within the bundle sheath cells, and the 3-C product is returned to the mesophyll cells, where it is reconverted to PEP in preparation to accept another COg (Figure 22.30). Plants that use the C-4 pathway are termed C4 plants, in contrast to those plants with the conventional pathway of COg uptake (C3 plants). 

The tricarboxylic acid cycle not only takes up acetyl CoA from fatty acid degradation, but also supplies the material for the biosynthesis of fatty acids and isoprenoids. Acetyl CoA, which is formed in the matrix space of mitochondria by pyruvate dehydrogenase (see p. 134), is not capable of passing through the inner mitochondrial membrane. The acetyl residue is therefore condensed with oxaloacetate by mitochondrial citrate synthase to form citrate. This then leaves the mitochondria by antiport with malate (right see p. 212). In the cytoplasm, it is cleaved again by ATP-dependent citrate lyase [4] into acetyl-CoA and oxaloacetate. The oxaloacetate formed is reduced by a cytoplasmic malate dehydrogenase to malate [2], which then returns to the mitochondrion via the antiport already mentioned. Alternatively, the malate can be oxidized by malic enzyme" [5], with decarboxylation, to pyruvate. The NADPH+H formed in this process is also used for fatty acid biosynthesis. 

Malate dehydrogenase (oxaloacetate-decarboxylating, NADP" )— malic enzyme ... 

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). 

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)... 

Fig. 5.4. Two types of energy metabolism in cestodes. (a) Type 1 homolactate fermentation, (b) Type 2 Malate dismutation. Reaction 3 involves a carboxylation step decarboxylation occurs at 6, 7 and 10. Reducing equivalents are generated at reactions 6 and 7 one reducing equivalent is used at reaction 9. Thus, when the mitochondrial compartment is in redox balance and malate is the sole substrate, twice as much propionate as acetate is produced. Key 1, pyruvate kinase 2, lactate dehydrogenase 3, phosphoenolpyruvate carboxykinase 4, malate dehydrogenase 5, mitochondrial membrane 6 malic enzyme 7, pyruvate dehydrogenase complex 8, fumarase 9, fumarate reductase 10, succinate decarboxylase complex. indicates reactions at which ATP is synthesised from ADP cyt, cytosol mit, mitochondrion. (After Bryant Flockhart, 1986.)...

Subsequent metabolism of oxaloacetate (OAA) varies according to species. Three main types of C4 pathway are recognized, of which the most extensively studied is that shown by plants such as Zea mays (corn) (Fig. 2). In these plants (here called type-1 C4 plants) OAA is reduced to malate via NADP-malate dehydrogenase in mesophyll chloroplasts. Malate is then transported to bundle sheath chloroplasts and oxidatively decarboxylated by NADP-malic enzyme to produce pyruvate, CO2 and NADPH. Pyruvate is recycled to the mesophyll cells while the CO2 and NADPH are used in the RPP cycle in the bundle sheath chloroplast. The original C3 carbon acceptor (PEP) is regenerated from pyruvate in the mesophyll chloroplast by the activity of pyruvate, Pj dikinase [8] (Eq. 5). 

The Q pathway for the transport of CO2 starts in a mesophyll cell with the condensation of CO2 and phosphoenolpyruvate to form oxaloacetate, in a reaction catalyzed by phosphoenolpyruvate carboxylase. In some species, oxaloacetate is converted into malate by an NADP+-linked malate dehydrogenase. Malate goes into the bundle-sheath cell and is oxidatively decarboxylated within the chloroplasts by an NADP+-linked malate dehydrogenase. The released CO2 enters the Calvin cycle in the usual way by condensing with ribulose 1,5-bisphosphate. Pyruvate formed in this decarboxylation reaction returns to the mesophyll cell. Finally, phosphoenolpyruvate is formed from pyruvate by pyruvate-Pi dikinase. 

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