Malate dehydrogenase distribution

P. A. Fields, E. L. Rudomin and G. N. Somero, Temperature sensitivities of cytosolic malate dehydrogenases from native and invasive species of marine mussels (genus Mytilus) sequence-function linkages and correlations with biogeographic distribution, J. Exp. Biol, 2006, 209, 656-667. 

Fig. 6. Distribution after centrifugation in a sucrose density gradient of activities of the five aromatic synthetic enzymes encoded in the arom cluster in N. crassa (and of the reference activity—Neurospora malate dehydrogenase) from an arom9 qal mutant [47], This mutant has very low constitutive DHQase activity (about 8% of wild type).

Rocha, V., Ting, I. P. Tissue distribution of microbody, mitochondrial, and soluble malate dehydrogenase isoenzymes. Plant Physiol. 46,754-756 (1970)... 

Fig. 2. Subcellular distribution of a-oxidation activity. Fractions were isolated by differential centrifugation of cucumber homogenate. Recoveries were between 71 and 84 % for the marker enzymes (A) malate dehydrogenase, (B) succinate cyt c reductase, (C) catalase, and 94 % for the (D) a-oxidation activity.

FIGURE 12.4 (a) Enzyme distribution in native chitosan scaffolds stained with fluorescein (green) combined with fluorescent (Alexa Fluor 546)-stained malate dehydrogenase (purple), (b) Enzyme distribution in butyl-modified chitosan scaffolds (same staining), (c) Enzyme distribution in ALA-modified chitosan scaffolds (same staining). (Reproduced with permission from Ref. [27]. Copyright 2009, American Chemical Society.)... 

Martin G, Minteer SD, Cooney MJ. Spatial distribution of malate dehydrogenase in chitosan scaffolds. ACS Appl Mater Interfaces 2009 1 367-372. 

Unlike glycolysis, which occurs strictly in the cell cytosol, gluconeogen-esis involves a complex interaction between the mitochondrion and the cytosol. This interaction is necessitated by the irreversibility of the pyruvate kinase reaction, by the relative impermeability of the inner mitochondrial membrane to oxaloacetate, and by the specific mitochondrial location of pyruvate carboxylase. Compartmentation within the cell has led to the distribution of a number of enzymes (aspartate and alanine aminotransferases, and NAD -malate dehydrogenase) in both the mitochondria and the cytosol. In the classical situation represented by the rat, mouse, or hamster hepatocyte, the indirect "translocation" of oxaloacetate—the product of the pyruvate carboxylase reaction—into the cytosol is effected by the concerted action of these enzymes. Within the mitochondria oxaloacetate is converted either to malate or aspartate, or both. Following the exit of these metabolites from the mitochondria, oxaloacetate is regenerated by essentially similar reactions in the cytosol and is subsequently decarboxylated to P-enolpyruvate by P-enol-pyruvate carboxykinase. Thus the presence of a membrane barrier to oxaloacetate leads to the functioning of the malate-aspartate shuttle as an important element in gluconeogenesis. 

Following are a set of assay conditions for marker enzymes of mitochondria (citrate synthetase, malic dehydrogenase, fumarase, and succinate dehydrogenase) and glyoxysomes (citrate synthetase, malate synthetase, and malic dehydrogenase). Some or all of these activities may be assayed across the density gradient. Their quantitative distribution is shown in Table 9-2. 

Salganicoff L, Koeppe RA (1968) Subcellular distribution of pyruvate carboxylase, diphosphopyridine nucleotide and triphosphopyridine nucleotide isocitrate dehydrogenases, and malate enzyme in rat brain. J Biol Chem 243 .34l6-3420. 

An alternate route utilises malate nicotinamide adenine dinucleotide phosphate (NADP) dehydrogenase (decarboxylating) to form malate, and then conversion to oxalacetate within the citric acid cycle to citrate. The relative importance of these two routes probably depends upon the subcellular distribution of the relevant enzymes in the tissue or subcellular organelle under study. This is referred to in detail in a later section. It should also be noted that pyruvate can be incorporated into the citric acid cycle either as oxalacetate or via acetyl CoA into citrate. This alternative applies only to the glycolytic pathway fatty acid oxidation, which is an alternate pathway of energy production, terminates with acetyl CoA which can only enter the citric acid cycle as citrate. 

Another overexpression strategy was tried with the NAD -dependent malic enzyme of E. coli Thermodynamically, the reduction of pyruvate to malate is favored, but in nature this reaction does not occur. A double mutant of E. coli, NZNlll, which is blocked in both pyruvate formate lyase pjT) and lactate dehydrogenase (Idh), was used as the host. It is unable to grow anaerobically because its pyruvate metabolism is blocked by the fermentation end products acetate, formate, ethanol, and lactic acid. The mutant NZNl 11 with multiple copies of malic enzyme accumulated succinic acid as a major end product only when the cells were switched to anaerobic metabolism gradually by metabolic depletion of oxygen in a sealed tube (Clark et al. 1988). Mutant strains blocked in either pfl or Idh did not alter their distribution of fermentation products when overexpressing malic enzyme. 

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