Enzyme malate dehydrogenase

The reaction mixture for a coupled assay includes the substrates for the initial or test enzyme and also the additional enzymes and reagents necessary to convert the product of the first reaction into a detectable product of the final reaction. The enzyme aspartate aminotransferase (EC 2.6.1.1), for instance, results in the formation of oxaloacetate, which can be converted to malic acid by the enzyme malate dehydrogenase (EC 1.1.1.37) with the simultaneous conversion of NADH to NAD+, a reaction which can be followed spectropho-tometrically at 340 nm ... 

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... 

Use the techniques outlined in the experimental procedure to explore two enzymes you will study in later experiments. Study the two enzymes malate dehydrogenase (Experiment 10) and tyrosinase (Experiment 5). View structures and look at amino acid sequences as you did for human a-lactalbumin. 

This step is catalyzed by a separate enzyme, malate dehydrogenase. It has a very unfavorable AG° of about +7 kcal/ mole. When this reaction is followed by reaction (17), the combined AG9 is about —1.3 kcal/mole, so the equilibrium constant for the overall sequence is favorable. You can view this simply as an illustration of the principle of mass action (17) pulls (18) along by removing one of the products. 

Enzymes (malate dehydrogenase, lactate dehydrogenase, isocitrate dehydrogenase, citrate lyase)... 

A second type of EMIT has been developed using the enzyme malate dehydrogenase as the enzymatic label. Research has shown that thyroxine competitively inhibits malate dehydrogenase. A conjugate prepared with thyroxine covalently bound close to the enzyme s active site shows very low specific activity that can be restored by binding of the thyroxine to arcP -thyroxine antibody. In this very specific assay for thyroxine, enzyme activity increases upon antibody binding, so that in a competitive assay for free thyroxine, activity decreases with increasing free thyroxine concentration. 

L-Malate + NAD+ <=> Oxaloacetate + NADH + H+ Enzyme Malate Dehydrogenase... 

L-malate is converted to oxaloacetate by action of the enzyme malate dehydrogenase. NADH is another product of this reaction. The same reactions occur in the urea cycle as well. 

Step 8. Regeneration of Oxaioacetate—Final Oxidation Step Malate is oxidized to oxaioacetate, and another molecule of NAD+ is reduced to NADH. This reaction is catalyzed by the enzyme malate dehydrogenase. The oxaioacetate can then react with another molecule of acetyl-GoA to start another round of the cycle. 

The mitochondrial enzyme malate dehydrogenase and the cytoplasmic version of malate dehydrogenase catalyze the same reaction (and hence have the same name) but their sequences and three-dimensional structures show no relationship. Explain how this can be ... 

The stereospecific formation of the S enantiomer of malic acid from fumaric acid also occurs in the tricarboxylic acid (TCA) cycle. The (5)-(-)-malic acid that is produced is converted to oxaloacetic acid by the enzyme malate dehydrogenase. 

Glutamate dehydrogenase Isocitrate dehydrogenase Ketogenesis enzymes Malate dehydrogenase Ornithine transcarbamylase Pyruvate carboxylase... 

Following an abrupt transition of P. pentosaceum from anaerobic to aerobic metabolism (10 pM O2), the growth rate increases at first, but the formation of acetate from lactate and glucose is slowed down, propionate formation is completely repressed and pyruvate is accumulated in the medium (van Gent-Ruijters et al, 1976 Schwartz et al, 1976). A decrease in the activities of the citric acid cycle enzymes malate dehydrogenase, fumarase and NADH oxidase, lactate oxidase, NADH-dependent fiimarate reductase, lactate-dependent nitrate reductase is observed upon the transition from anaerobic to aerobic (10 pM O2) metabolism (van Gent-Ruijters, 1975). 

As the cotyledonary reserves are consumed the mitochondria become disorganized and gradually lose their respiratory efficiency, enzyme complement and activity. In cotyledons of dark-grown Alaska peas this is marked by a decline in respiratory control (Fig. 5.7A), a loss of efficiency of oxidative phosphorylation (shown by the fall in ADP/0 ratio) (Fig. 5.7 B) and in cytochrome oxidase activity (Fig. 5.7 C). Another mitochondrial enzyme, malate dehydrogenase does not decline however. The gradual loss of mitochondrial activity is accompanied by the disruption of cell structure (see Chap. 6). 

A similar pathway for the formation of sucdnate in both Actinobadllus sp. 130Z and A. sucdniciproducens has been proposed. The formation of oxalacetate fi-om PEP via CO2 fixation is the first key step. The enzymes malate dehydrogenase, fumarase, and fumarate reductase, all enzymes of the tricarboxylic acid (TCA) cycle, work in a reductive fashion toward succinate (Van der Werf et al. 1997 Samuelov et al. 1991). The reactions catalyzed are as follows ... 

Electrostatic channeling of a substrate between two enzymatic active sites has recently been studied by Brownian dynamics for citric acid cycle enzymes malate dehydrogenase and citrate synthase,and in the bifunctional enzyme... 

Water is added across the double bond of fumarate in a reaction which is catalyzed by the enzyme fumarase. The reaction is reversible, although slightly exer-gonic. At equilibrium there is 82% immolate. In the ninth and last step of the cycle, the secondary hydroxyl group of malate is dehydrogenated. The enzyme malate dehydrogenase transfers the hydrogen to NAD. The product of this reaction is oxaloacetate, the primer for the whole chain of reactions. The cycle is closed and we have finished one trip around it. 

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