Malic enzyme distribution

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. 

This reversible carboxylation is catalyzed by an enzyme, first found in pigeon liver, which specifically requires TPN and manganous ions for activity (267). Further study showed that this enzyme, referred to as malic enzyme, is widely distributed in animal and plant tissues and in bacterial cells. Experiments with highly... 

In the analysis of fruit juices, it is important to determine the levels of the individual acids to assess authenticity and quality. A range of these acids can be determined using an enzyme-linked assays and these procedures have been collaboratively tested and published in the IFU compendium of methods (citric no. 22, isocitric no. 54, D-malic no. 64, L-malic no. 21 and D-and L-lactic acids no. 53). r-Biopharm now distributes the Boehringer Mannheim kits to assess the levels of these acids. Similar kits are available from other suppliers. 

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. 

Ogston has recently put forward an idea which removes the difficulty of ascribing both reactions to one enzyme. It is a development of his theory discussed above of a three-point combination between enzyme and substrate. As already explained, the fumarate molecule in order to yield optically active malic acid must be so placed on the enzyme surface that only one double-bond component can react, but no direction need be exerted on the water in which H and OH are distributed. If it is now assumed that aconitase is constructed analogously to fumarase in that again no direction is exerted on the elements of water when they combine with aconitic acid, it is seen at once that two different compounds arise, namely, citric and isocitric acids. The occurrence of the reverse reaction would follow from the requirement of catalytic reversibility. 

The Oxaloacetic System (Szent-Gyoi i, 1937).— The wide distribution of the three enzymes, succinic and malic dehydrogenase, and fumarase, si ests that they and their respective substrates participate in many tissue respirations. Addition of malonic acid, which inhibits succinic acid oxidation, leads to an almost complete... 

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